Apache NiFi - MiNiFi - C++ supports a subset of the Apache NiFi Expression Language (EL). EL is a tiny DSL enabling processor property values to be computed dynamically according to contextual information such as FlowFile attributes. Dynamic values may be manipulated by a number of functions supported by EL, including boolean logic, string manipulation, encoding/decoding, searching, mathematical operators, date manipulation, type coercion, and more. Processors/properties supporting EL are marked in the processors documentation.
All data in Apache NiFi is represented by an abstraction called a FlowFile. A FlowFile comprises two major pieces: content and attributes. The content portion of the FlowFile represents the data on which to operate. For instance, if a file is picked up from a local file system using the GetFile Processor, the contents of the file will become the contents of the FlowFile.
The attributes portion of the FlowFile represents information about the data itself, or metadata. Attributes are key-value pairs that represent what is known about the data as well as information that is useful for routing and processing the data appropriately. Keeping with the example of a file that is picked up from a local file system, the FlowFile would have an attribute called filename that reflected the name of the file on the file system. Additionally, the FlowFile will have a path attribute that reflects the directory on the file system that this file lived in. The FlowFile will also have an attribute named uuid, which is a unique identifier for this FlowFile. For complete listing of the core attributes check out the FlowFile section of the Apache NiFi Developer’s Guide.
However, placing these attributes on a FlowFile do not provide much benefit if the user is unable to make use of them. The NiFi Expression Language provides the ability to reference these attributes, compare them to other values, and manipulate their values.
The NiFi Expression Language always begins with the start delimiter ${ and ends with the end delimiter }. Between the start and end delimiters is the text of the Expression itself. In its most basic form, the Expression can consist of just an attribute name. For example, ${filename} will return the value of the filename attribute.
In a slightly more complex example, we can instead return a manipulation of this value. We can, for example, return an all upper-case version of the filename by calling the toUpper function: ${filename:toUpper()}. In this case, we reference the filename attribute and then manipulate this value by using the toUpper function. A function call consists of 5 elements. First, there is a function call delimiter :. Second is the name of the function --in this case, toUpper. Next is an open parenthesis ((), followed by the function arguments. The arguments necessary are dependent upon which function is being called. In this example, we are using the toUpper function, which does not have any arguments, so this element is omitted. Finally, the closing parenthesis ()) indicates the end of the function call. There are many different functions that are supported by the Expression Language to achieve many different goals. Some functions provide String (text) manipulation, such as the toUpper function. Others, such as the equals and matches functions, provide comparison functionality. Functions also exist for manipulating dates and times and for performing mathematical operations. Each of these functions is described below, in the Functions section, with an explanation of what the function does, the arguments that it requires, and the type of information that it returns.
When we perform a function call on an attribute, as above, we refer to the attribute as the subject of the function, as the attribute is the entity on which the function is operating. We can then chain together multiple function calls, where the return value of the first function becomes the subject of the second function and its return value becomes the subject of the third function and so on. Continuing with our example, we can chain together multiple functions by using an expression similar to ${filename:toUpper():equals('HELLO.TXT')}. There is no limit to the number of functions that can be chained together.
Any FlowFile attribute can be referenced using the Expression Language. However, if the attribute name contains a special character, the attribute name must be escaped by quoting it. The following characters are each considered special characters:
$ (dollar sign)| (pipe){ (open brace)} (close brace)( (open parenthesis)) (close parenthesis)[ (open bracket)] (close bracket), (comma): (colon); (semicolon)/ (forward slash)* (asterisk)' (single quote) (space)\t (tab)\r (carriage return)\n (new-line)Additionally, a number is considered a special character if it is the first character of the attribute name. If any of these special characters is present in an attribute is quoted by using either single or double quotes. The Expression Language allows single quotes and double quotes to be used interchangeably. For example, the following can be used to escape an attribute named my attribute: ${"my attribute"} or ${'my attribute'}.
In this example, the value to be returned is the value of the “my attribute” value, if it exists. If that attribute does not exist, the Expression Language will then look for a System Environment Variable named “my attribute.” Finally, if none of these exists, the Expression Language will return a null value.
There also exist some functions that expect to have no subject. These functions are invoked simply by calling the function at the beginning of the Expression, such as ${hostname()}. These functions can then be changed together, as well. For example, ${hostname():toUpper()}. Attempting to evaluate the function with subject will result in an error. In the Functions section below, these functions will clearly indicate in their descriptions that they do not require a subject.
Often times, we will need to compare the values of two different attributes to each other. We are able to accomplish this by using embedded Expressions. We can, for example, check if the filename attribute is the same as the uuid attribute: ${filename:equals( ${uuid} )}. Notice here, also, that we have a space between the opening parenthesis for the equals method and the embedded Expression. This is not necessary and does not affect how the Expression is evaluated in any way. Rather, it is intended to make the Expression easier to read. White space is ignored by the Expression Language between delimiters. Therefore, we can use the Expression ${ filename : equals(${ uuid}) } or ${filename:equals(${uuid})} and both Expressions mean the same thing. We cannot, however, use ${file name:equals(${uuid})}, because this results in file and name being interpreted as different tokens, rather than a single token, filename.
toUppertoLowersubstringsubstringBeforesubstringBeforeLastsubstringAftersubstringAfterLastgetDelimitedFieldreplacereplaceFirstreplaceAllreplaceNullreplaceEmptytrimappendprependlengthescapeJsonunescapeJsonescapeXmlescapeCsvunescapeXmlunescapeCsvurlEncodeurlDecodebase64Encodebase64DecodeanyAttributeallAttributesanyMatchingAttributeallMatchingAttributesanyDelineatedValueallDelineatedValuesjoincountjsonPathescapeHtml3escapeHtml4unescapeHtml3unescapeHtml4nextIntgetStateValueThe following EL features are currently not supported, and no support is planned due to language/environment (Java vs. C++) differences:
mathOne of the most powerful features of the Expression Language is the ability to compare an attribute value against some other value. This is used often, for example, to configure how a Processor should route data. The following functions are used for performing boolean logic, such as comparing two values. Each of these functions are designed to work on values of type Boolean.
Description: The isNull function returns true if the subject is null, false otherwise. This is typically used to determine if an attribute exists.
Subject Type: Any
Arguments: No arguments
Return Type: Boolean
Examples: ${filename:isNull()} returns true if the filename attribute does not exist. It returns false if the attribute exists.
Description: The notNull function returns the opposite value of the isNull function. That is, it will return true if the subject exists and false otherwise.
Subject Type: Any
Arguments: No arguments
Return Type: Boolean
Examples: ${filename:notNull()} returns true if the filename attribute exists. It returns false if the attribute does not exist.
Description: The isEmpty function returns true if the Subject is null, does not contain any characters or contains only white-space (new line, carriage return, space, tab), false otherwise.
Subject Type: String
Arguments: No arguments
Return Type: Boolean
Examples: ${filename:isEmpty()} returns true if the filename attribute does not exist or contains only white space. ${literal(" "):isEmpty()} returns true as well as ${literal(""):isEmpty()}.
Description: The equals function is very widely used and determines if its subject is equal to another String value. Note that the equals function performs a direct comparison of two String values. Take care not to confuse this function with the matches function, which evaluates its subject against a Regular Expression.
Subject Type: Any
Arguments:
| Argument | Description |
|---|---|
| value | The value to compare the Subject to. Must be same type as the Subject. |
Return Type: Boolean
Examples: We can check if the filename of a FlowFile is hello.txt by using the expression ${filename:equals('hello.txt')}, or we could check if the value of the attribute hello is equal to the value of the filename attribute: ${hello:equals( ${filename} )}.
Description: Similar to the equals function, the equalsIgnoreCase function compares its subject against a String value but returns true if the two values differ only by case (upper case vs. lower case).
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The value to compare the Subject to. |
Return Type: Boolean
Examples: ${filename:equalsIgnoreCase('hello.txt')} will evaluate to true if filename is equal to hello.txt or HELLO.TXT or HeLLo.TxT.
Description: The gt function is used for numeric comparison and returns true if the subject is Greater Than its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.
Subject Type: Number
Arguments:
| Argument | Description |
|---|---|
| value | The number to compare the Subject to. |
Return Type: Boolean
Examples: ${fileSize:gt( 1024 )} will return true if the size of the FlowFile’s content is more than 1 kilobyte (1024 bytes). Otherwise, it will return false.
Description: The ge function is used for numeric comparison and returns true if the subject is Greater Than Or Equal To its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.
Subject Type: Number
Arguments:
| Argument | Description |
|---|---|
| value | The number to compare the Subject to. |
Return Type: Boolean
Examples: ${fileSize:ge( 1024 )} will return true if the size of the FlowFile’s content is at least ( is greater than or equal to) 1 kilobyte (1024 bytes). Otherwise, it will return false.
Description: The lt function is used for numeric comparison and returns true if the subject is Less Than its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.
Subject Type: Number
Arguments:
| Argument | Description |
|---|---|
| value | The number to compare the Subject to. |
Return Type: Boolean
Examples: ${fileSize:lt( 1048576 )} will return true if the size of the FlowFile’s content is less than 1 megabyte (1048576 bytes). Otherwise, it will return false.
Description: The le function is used for numeric comparison and returns true if the subject is Less Than Or Equal To its argument. If either the subject or the argument cannot be coerced into a Number, this function returns false.
Subject Type: Number
Arguments:
| Argument | Description |
|---|---|
| value | The number to compare the Subject to. |
Return Type: Boolean
Examples: ${fileSize:le( 1048576 )} will return true if the size of the FlowFile’s content is at most (less than or equal to) 1 megabyte (1048576 bytes). Otherwise, it will return false.
Description: The and function takes as a single argument a Boolean value and returns true if both the Subject and the argument are true. If either the subject or the argument is false or cannot be coerced into a Boolean, the function returns false. Typically, this is used with an embedded Expression as the argument.
Subject Type: Boolean
Arguments:
| Argument | Description |
|---|---|
| condition | The right-hand-side of the and Expression |
Return Type: Boolean
Examples: We can check if the filename is both all lower-case and has at least 5 characters by using the Expression
${filename:toLower():equals( ${filename} ):and(
${filename:length():ge(5)}
)}
Description: The or function takes as a single argument a Boolean value and returns true if either the Subject or the argument is true. If both the subject and the argument are false, the function returns false. If either the Subject or the argument cannot be coerced into a Boolean value, this function will return false.
Subject Type: Boolean
Arguments:
| Argument | Description |
|---|---|
| condition | The right-hand-side of the or Expression |
Return Type: Boolean
Examples: The following example will return true if either the filename has exactly 5 characters or if the filename is all lower-case.
${filename:toLower():equals( ${filename} ):or(
${filename:length():equals(5)}
)}
Description: The not function returns the negation of the Boolean value of the subject.
Subject Type: Boolean
Arguments: No arguments
Return Type: Boolean
Examples: We can invert the value of another function by using the not function, as ${filename:equals('hello.txt'):not()}. This will return true if the filename is NOT equal to hello.txt and will return false if the filename is hello.txt.
Description: Evaluates the first argument if the Subject evaluates to true, or the second argument if the Subject evaluates to false.
Subject Type: Boolean
| Argument | Description |
|---|---|
| EvaluateIfTrue | The value to return if the Subject is true |
| EvaluateIfFalse | The value to return if the Subject is false |
Return Type: String
Examples:
If the filename attribute has the value a brand new filename.txt, the nullFilename attribute has the value null, and the bool attribute has the value true, then the following expressions will provide the following results:
| Expression | Value |
|---|---|
${bool:ifElse('a','b')} | a |
${literal(true):ifElse('a','b')} | a |
${nullFilename:isNull():ifElse('file does not exist', 'located file')} | file does not exist |
${nullFilename:ifElse('found', 'not_found')} | not_found |
${filename:ifElse('found', 'not_found')} | not_found |
${filename:isNull():not():ifElse('found', 'not_found')} | found |
Each of the following functions manipulates a String in some way.
Description: This function converts the Subject into an all upper-case String. Said another way, it replaces any lowercase letter with the uppercase equivalent.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples: If the filename attribute is abc123.txt, then the Expression ${filename:toUpper()} will return ABC123.TXT
Description: This function converts the Subject into an all lower-case String. Said another way, it replaces any uppercase letter with the lowercase equivalent.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples: If the filename attribute is ABC123.TXT, then the Expression ${filename:toLower()} will return abc123.txt
Description: Returns a portion of the Subject, given a starting index and an optional ending index. If the ending index is not supplied, it will return the portion of the Subject starting at the given ‘start index’ and ending at the end of the Subject value.
The starting index and ending index are zero-based. That is, the first character is referenced by using the value 0, not 1.
If either the starting index is or the ending index is not a number, this function call will result in an error.
If the starting index is larger than the ending index, this function call will result in an error.
If the starting index or the ending index is greater than the length of the Subject or has a value less than 0, this function call will result in an error.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| starting index | The 0-based index of the first character to capture (inclusive) |
| ending index | The 0-based index of the last character to capture (exclusive) |
Return Type: String
Examples:
If we have an attribute named filename with the value a brand new filename.txt, then the following Expressions will result in the following values:
| Expression | Value |
|---|---|
${filename:substring(0,1)} | a |
${filename:substring(2)} | brand new filename.txt |
${filename:substring(12)} | filename.txt |
${filename:substring( ${filename:length():minus(2)} )} | xt |
Description: Returns a portion of the Subject, starting with the first character of the Subject and ending with the character immediately before the first occurrence of the argument. If the argument is not present in the Subject, the entire Subject will be returned.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The String to search for in the Subject |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will result in the following values:
| Expression | Value |
|---|---|
${filename:substringBefore('.')} | a brand new filename |
${filename:substringBefore(' ')} | a |
${filename:substringBefore(' n')} | a brand |
${filename:substringBefore('missing')} | a brand new filename.txt |
Description: Returns a portion of the Subject, starting with the first character of the Subject and ending with the character immediately before the last occurrence of the argument. If the argument is not present in the Subject, the entire Subject will be returned.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The String to search for in the Subject |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will result in the following values:
| Expression | Value |
|---|---|
${filename:substringBeforeLast('.')} | a brand new filename |
${filename:substringBeforeLast(' ')} | a brand new |
${filename:substringBeforeLast(' n')} | a brand |
${filename:substringBeforeLast('missing')} | a brand new filename.txt |
Description: Returns a portion of the Subject, starting with the character immediately after the first occurrence of the argument and extending to the end of the Subject. If the argument is not present in the Subject, the entire Subject will be returned.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The String to search for in the Subject |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will result in the following values:
| Expression | Value |
|---|---|
${filename:substringAfter('.')} | txt |
${filename:substringAfter(' ')} | brand new filename.txt |
${filename:substringAfter(' n')} | ew filename.txt |
${filename:substringAfter('missing')} | a brand new filename.txt |
Description: Returns a portion of the Subject, starting with the character immediately after the last occurrence of the argument and extending to the end of the Subject. If the argument is not present in the Subject, the entire Subject will be returned.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The String to search for in the Subject |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will result in the following values:
| Expression | Value |
|---|---|
${filename:substringAfterLast('.')} | txt |
${filename:substringAfterLast(' ')} | filename.txt |
${filename:substringAfterLast(' n')} | ew filename.txt |
${filename:substringAfterLast('missing')} | a brand new filename.txt |
Description: Parses the Subject as a delimited line of text and returns just a single field from that delimited text.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| index | The index of the field to return. A value of 1 will return the first field, a value of 2 will return the second field, and so on. |
| delimiter | Optional argument that provides the character to use as a field separator. If not specified, a comma will be used. This value must be exactly 1 character. |
| quoteCHar | Optional argument that provides the character that can be used to quote values so that the delimiter can be used within a single field. If not specified, a double-quote (") will be used. This value must be exactly 1 character. |
| escapeChar | Optional argument that provides the character that can be used to escape the Quote Character or the Delimiter within a field. If not specified, a backslash () is used. This value must be exactly 1 character. |
| stripChars | Optional argument that specifies whether or not quote characters and escape characters should be stripped. For example, if we have a field value "1, 2, 3" and this value is true, we will get the value 1, 2, 3, but if this value is false, we will get the value "1, 2, 3" with the quotes. The default value is false. This value must be either true or false. |
Return Type: String
Examples: If the “line” attribute contains the value “Jacobson, John”, 32, Mr. and the “altLine” attribute contains the value Jacobson, John|32|Mr. then the following Expressions will result in the following values:
| Expression | Value |
|---|---|
${line:getDelimitedField(2)} | 32 |
${line:getDelimitedField(2):trim()} | 32 |
${line:getDelimitedField(1)} | "Jacobson, John" |
${line:getDelimitedField(1, ',', '"', '\\', true)} | Jacobson, John |
| `${altLine:getDelimitedField(1, ' | ')}` |
Description: Replaces all occurrences of one literal String within the Subject with another String.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Search String | The String to find within the Subject |
| Replacement | The value to replace Search String with |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:replace('.', '_')} | a brand new filename_txt |
${filename:replace(' ', '.')} | a.brand.new.filename.txt |
${filename:replace('XYZ', 'ZZZ')} | a brand new filename.txt |
${filename:replace('filename', 'book')} | a brand new book.txt |
Description: Replaces the first occurrence of one literal String or regular expression within the Subject with another String.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Search String | The String (literal or regular expression pattern) to find within the Subject |
| Replacement | The value to replace Search String with |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:replaceFirst('a', 'the')} | the brand new filename.txt |
${filename:replaceFirst('[br]', 'g')} | a grand new filename.txt |
${filename:replaceFirst('XYZ', 'ZZZ')} | a brand new filename.txt |
${filename:replaceFirst('\w{8}', 'book')} | a brand new book.txt |
Description: The replaceAll function takes two String arguments: a literal String or Regular Expression (NiFi uses the Java Pattern syntax), and a replacement string. The return value is the result of substituting the replacement string for all patterns within the Subject that match the Regular Expression.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Regex | he Regular Expression (in Java syntax) to match in the Subject |
| Replacement | The value to use for replacing matches in the Subject. If the regular expression argument uses Capturing Groups, back references are allowed in the replacement. |
Return Type: String
Examples: If the filename attribute has the value a brand new filename.txt, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:replaceAll('\..*', '')} | a brand new filename |
${filename:replaceAll('a brand (new)', '$1')} | new filename.txt |
${filename:replaceAll('XYZ', 'ZZZ')} | a brand new filename.txt |
${filename:replaceAll('brand (new)', 'somewhat $1')} | a somewhat new filename.txt |
Description: The replaceNull function returns the argument if the Subject is null. Otherwise, returns the Subject.
Subject Type: Any
Arguments:
| Argument | Description |
|---|---|
| Replacement | The value to return if the Subject is null. |
Return Type: Type of Subject if Subject is not null; else, type of Argument
Examples: If the attribute filename has the value a brand new filename.txt and the attribute hello does not exist, then the Expression ${filename:replaceNull('abc')} will return a brand new filename.txt, while ${hello:replaceNull('abc')} will return abc.
Description: The replaceEmpty function returns the argument if the Subject is null or if the Subject consists only of white space (new line, carriage return, tab, space). Otherwise, returns the Subject.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Replacement | The value to return if the Subject is null or empty. |
Return Type: String
Examples: If the attribute filename has the value a brand new filename.txt and the attribute hello has the value , then the Expression ${filename:replaceEmpty('abc')} will return a brand new filename.txt, while ${hello:replaceEmpty('abc')} will return abc.
Description: The trim function will remove any leading or trailing white space from its subject.
Subject Type: String
Arguments: No Arguments
Return Type: String
Examples: If the attribute attr has the value " 1 2 3 ", then the Expression ${attr:trim()} will return the value “1 2 3”.
Description: The append function returns the result of appending the argument to the value of the Subject. If the Subject is null, returns the argument itself.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The String to append to the end of the Subject |
Return Type: String
Examples: If the “filename” attribute has the value “a brand new filename.txt”, then the Expression ${filename:append('.gz')} will return “a brand new filename.txt.gz”.
Description: The prepend function returns the result of prepending the argument to the value of the Subject. If the subject is null, returns the argument itself.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The String to prepend to the beginning of the Subject |
Return Type: String
Examples: If the “filename” attribute has the value “filename.txt”, then the Expression ${filename:prepend('a brand new ')} will return “a brand new filename.txt”.
Description: Returns the length of the Subject
Subject Type: String
Arguments: No arguments
Return Type: String
Examples: If the attribute “filename” has a value of “a brand new filename.txt” and the attribute “hello” does not exist, then the Expression ${filename:length()} will return 24. ${hello:length()} will return 0.
For those functions that support Decimal and Number (whole number) types, the return value type depends on the input types. If either the subject or argument are a Decimal then the result will be a Decimal. If both values are Numbers then the result will be a Number. This includes Divide. This is to preserve backwards compatibility and to not force rounding errors.
Description: Adds a numeric value to the Subject. If either the argument or the Subject cannot be coerced into a Number, returns null.
Subject Type: Number or Decimal
Arguments:
| Argument | Description |
|---|---|
| Operand | The value to add to the Subject |
Return Type: Number or Decimal (depending on input types)
Examples: If the fileSize attribute has a value of 100, then the Expression ${fileSize:plus(1000)} will return the value 1100.
Description: Subtracts a numeric value from the Subject.
Subject Type: Number or Decimal
Arguments:
| Argument | Description |
|---|---|
| Operand | The value to subtract from the Subject |
Return Type: Number or Decimal (depending on input types)
Examples: If the fileSize attribute has a value of 100, then the Expression ${fileSize:minus(100)} will return the value 0.
Description: Multiplies a numeric value by the Subject and returns the product.
Subject Type: Number or Decimal
Arguments:
| Argument | Description |
|---|---|
| Operand | The value to multiple the Subject by |
Return Type: Number or Decimal (depending on input types)
Examples: If the fileSize attribute has a value of 100, then the Expression ${fileSize:multiply(1024)} will return the value 102400.
Description: Divides the Subject by a numeric value and returns the result.
Subject Type: Number or Decimal
Arguments:
| Argument | Description |
|---|---|
| Operand | The value to divide the Subject by |
Return Type: Number or Decimal (depending on input types)
Examples: If the fileSize attribute has a value of 100, then the Expression ${fileSize:divide(12)} will return the value 8.
Description: Performs a modular division of the Subject by the argument. That is, this function will divide the Subject by the value of the argument and return not the quotient but rather the remainder.
Subject Type: Number or Decimal
Arguments:
| Argument | Description |
|---|---|
| Operand | The value to divide the Subject by |
Return Type: Number or Decimal (depending on input types)
Examples: If the fileSize attribute has a value of 100, then the Expression ${fileSize:mod(12)} will return the value 4.
Description: Converts the Subject from a Base 10 number to a different Radix (or number base). An optional second argument can be used to indicate the minimum number of characters to be used. If the converted value has fewer than this number of characters, the number will be padded with leading zeroes.
If a decimal is passed as the subject, it will first be converted to a whole number and then processed.
Subject Type: Number
Arguments:
| Argument | Description |
|---|---|
| Desired Base | A Number between 2 and 36 (inclusive) |
| Padding | Optional argument that specifies the minimum number of characters in the converted output |
Return Type: String
Examples: If the fileSize attributes has a value of 1024, then the following Expressions will yield the following results:
| Expression | Value |
|---|---|
${fileSize:toRadix(10)} | 1024 |
${fileSize:toRadix(10, 1)} | 1024 |
${fileSize:toRadix(10, 8)} | 00001024 |
${fileSize:toRadix(16)} | 400 |
${fileSize:toRadix(16, 8)} | 00000400 |
${fileSize:toRadix(2)} | 10000000000 |
${fileSize:toRadix(2, 16)} | 0000010000000000 |
Description: Converts the Subject from a specified Radix (or number base) to a base ten whole number. The subject will converted as is, without interpretation, and all characters must be valid for the base being converted from. For example converting “0xFF” from hex will not work due to “x” being a invalid hex character.
If a decimal is passed as the subject, it will first be converted to a whole number and then processed.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Subject Base | A Number between 2 and 36 (inclusive) |
Return Type: Number
Examples: If the fileSize attributes has a value of 1234A, then the following Expressions will yield the following results:
| Expression | Value |
|---|---|
${fileSize:fromRadix(11)} | 17720 |
${fileSize:fromRadix(16)} | 74570 |
${fileSize:fromRadix(20)} | 177290 |
Description: Returns a random whole number (0 to 2^63 - 1) using an insecure random number generator.
Subject Type: No subject
Arguments: No arguments
Return Type: Number
Examples: ${random():mod(10):plus(1)} returns random number between 1 and 10 inclusive.
Description: Returns true if the Subject starts with the String provided as the argument, false otherwise.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The value to search for |
Return Type: Boolean
Examples:
If the “filename” attribute has the value “a brand new filename.txt”, then the Expression ${filename:startsWith('a brand')} will return true. ${filename:startsWith('A BRAND')} will return false. ${filename:toUpper():startsWith('A BRAND')} returns true.
Description: Returns true if the Subject ends with the String provided as the argument, false otherwise.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The value to search for |
Return Type: Boolean
Examples:
If the “filename” attribute has the value “a brand new filename.txt”, then the Expression ${filename:endsWith('txt')} will return true. ${filename:endsWith('TXT')} will return false. ${filename:toUpper():endsWith('TXT')} returns true.
Description: Returns true if the Subject contains the value of the argument anywhere in the value.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The value to search for |
Return Type: Boolean
Examples:
If the “filename” attribute has the value “a brand new filename.txt”, then the Expression ${filename:contains('new')} will return true. ${filename:contains('NEW')} will return false. ${filename:toUpper():contains('NEW')} returns true.
Description: Returns true if the Subject is matching one of the provided arguments.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value1 | First possible matching value |
| valueN | Nth possible matching value |
Return Type: Boolean
Examples:
If the “myEnum” attribute has the value “JOHN”, then the Expression ${myEnum:in("PAUL", "JOHN", "MIKE")} will return true. ${myEnum:in("RED", "GREEN", "BLUE")} will return false.
Description: Returns true if the Subject contains any sequence of characters that matches the Regular Expression provided by the argument.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Regex | The Regular Expression to match against the Subject |
Return Type: Boolean
Examples:
If the filename attribute has the value “a brand new filename.txt”, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:find('a [Bb]rand [Nn]ew')} | true |
${filename:find('Brand.*')} | false |
${filename:find('brand')} | true |
Description: Returns true if the Subject exactly matches the Regular Expression provided by the argument.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Regex | The Regular Expression to match against the Subject |
Return Type: Boolean
Examples:
If the filename attribute has the value “a brand new filename.txt”, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:matches('a.*txt')} | true |
${filename:matches('brand')} | false |
${filename:matches('.brand.')} | true |
Description: Returns the index of the first character in the Subject that matches the String value provided as an argument. If the argument is found multiple times within the Subject, the value returned is the starting index of the first occurrence. If the argument cannot be found in the Subject, returns -1. The index is zero-based. This means that if the search string is found at the beginning of the Subject, the value returned will be 0, not 1.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The value to search for in the Subject |
Return Type: Boolean
Examples:
If the filename attribute has the value “a brand new filename.txt”, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:indexOf('a.*txt')} | -1 |
${filename:indexOf('.')} | 20 |
${filename:indexOf('a')} | 0 |
${filename:indexOf(' ')} | 1 |
Description: Returns the index of the first character in the Subject that matches the String value provided as an argument. If the argument is found multiple times within the Subject, the value returned is the starting index of the last occurrence. If the argument cannot be found in the Subject, returns -1. The index is zero-based. This means that if the search string is found at the beginning of the Subject, the value returned will be 0, not 1.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| value | The value to search for in the Subject |
Return Type: Boolean
Examples:
If the filename attribute has the value “a brand new filename.txt”, then the following Expressions will provide the following results:
| Expression | Value |
|---|---|
${filename:lastIndexOf('a.*txt')} | -1 |
${filename:lastIndexOf('.')} | 20 |
${filename:lastIndexOf('a')} | 17 |
${filename:lastIndexOf(' ')} | 11 |
Each of the following functions will encode a string according the rules of the given data format.
Description: This function prepares the Subject to be inserted into JSON document by escaping the characters in the String using Json String rules. The function correctly escapes quotes and control-chars (tab, backslash, cr, ff, etc.)
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If the “message” attribute is ‘This is a “test!”’, then the Expression ${message:escapeJson()} will return ‘This is a "test!"’
Description: This function unescapes any Json literals found in the String.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If the “message” attribute is ‘This is a "test!"’, then the Expression ${message:unescapeJson()} will return ‘This is a “test!”’
Description: This function prepares the Subject to be inserted into XML document by escaping the characters in a String using XML entities. The function correctly escapes quotes, apostrophe, ampersand, <, > and control-chars.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If the “message” attribute is Zero > One < \"two!\" & 'true', then the Expression ${message:escapeXml()} will return Zero > One < "two!" & 'true'
Description: This function unescapes a string containing XML entity escapes to a string containing the actual Unicode characters corresponding to the escapes. Supports only the five basic XML entities (gt, lt, quot, amp, apos).
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If the “message” attribute is Zero > One < "two!" & 'true', then the Expression ${message:escapeXml()} will return Zero > One < \"two!\" & 'true'
Description: This function prepares the Subject to be inserted into CSV document by escaping the characters in a String using the rules in RFC 4180. The function correctly escapes quotes and surround the string in quotes if needed.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If the “message” attribute is Zero > One < "two!" & 'true', then the Expression ${message:escapeCsv()} will return "Zero > One < ""two!"" & 'true'"
Description: This function unescapes a String from a CSV document according to the rules of RFC 4180
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If the “message” attribute is "Zero > One < ""two!"" & 'true'", then the Expression ${message:escapeCsv()} will return Zero > One < "two!" & 'true'
Description: Returns a URL-friendly version of the Subject. This is useful, for instance, when using an attribute value to indicate the URL of a website.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
We can URL-Encode an attribute named “url” by using the Expression ${url:urlEncode()}. If the value of the “url” attribute is “some value with spaces”, this Expression will then return “some%20value%20with%20spaces”.
Description: Converts a URL-friendly version of the Subject into a human-readable form.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If we have a URL-Encoded attribute named “url” with the value “some%20value%20with%20spaces”, then the Expression ${url:urlDecode()} will return “some value with spaces”.
Description: Returns a Base64 encoded string. This is useful for being able to transfer binary data as ascii.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
We can Base64-Encoded an attribute named “payload” by using the Expression ${payload:base64Encode()} If the attribute payload had a value of “admin:admin” then the Expression ${payload:base64Encode()} will return “YWRtaW46YWRtaW4=”.
Description: Reverses the Base64 encoding on given string.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples:
If we have a Base64-Encoded attribute named “payload” with the value “YWRtaW46YWRtaW4=”, then the Expression ${payload:base64Decode()} will return “admin:admin”.
While the majority of functions in the Expression Language are called by using the syntax ${attributeName:function()}, there exist a few functions that are not expected to have subjects. In this case, the attribute name is not present. For example, the IP address of the machine can be obtained by using the Expression ${ip()}. All of the functions in this section are to be called without a subject. Attempting to call a subjectless function and provide it a subject will result in an error when validating the function.
Description: Returns the IP address of the machine.
Subject Type: No subject
Arguments: No arguments
Return Type: String
Examples: The IP address of the machine can be obtained by using the Expression ${ip()}.
Description: eturns the Hostname of the machine. An optional argument of type Boolean can be provided to specify whether or not the Fully Qualified Domain Name should be used. If false, or not specified, the hostname will not be fully qualified. If the argument is true but the fully qualified hostname cannot be resolved, the simple hostname will be returned.
Subject Type: No subject
Arguments:
| Argument | Description |
|---|---|
| Fully Qualified | Optional parameter that specifies whether or not the hostname should be fully qualified. If not specified, defaults to false. |
Return Type: String
Examples: The fully qualified hostname of the machine can be obtained by using the Expression ${hostname(true)}, while the simple hostname can be obtained by using either ${hostname(false)} or simply ${hostname()}.
Description: Returns a randomly generated UUID.
Subject Type: No subject
Arguments: No arguments
Return Type: String
Examples: ${UUID()} returns a value similar to “de305d54-75b4-431b-adb2-eb6b9e546013”
Description: Returns its argument as a literal String value. This is useful in order to treat a string or a number at the beginning of an Expression as an actual value, rather than treating it as an attribute name. Additionally, it can be used when the argument is an embedded Expression that we would then like to evaluate additional functions against.
Subject Type: No subject
Arguments:
| Argument | Description |
|---|---|
| value | The value to be treated as a literal string, number, or boolean value. |
Return Type: String
Examples: ${literal(2):gt(1)} returns true. ${literal( ${allMatchingAttributes('a.*'):count()} ):gt(3)} returns true if there are more than 3 attributes whose names begin with the letter a.
When it becomes necessary to evaluate the same conditions against multiple attributes, this can be accomplished by means of the and and or functions. However, this quickly becomes tedious, error-prone, and difficult to maintain. For this reason, NiFi Expression Language provides several functions for evaluating the same conditions against groups of attributes at the same time.
Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are the names of attributes to which the remainder of the Expression is to be applied. If any of the attributes specified, when evaluated against the rest of the Expression, returns a value of true, then this function will return true. Otherwise, this function will return false.
Subject Type: No Subject
Arguments:
| Argument | Description |
|---|---|
| Attribute Names | One or more attribute names to evaluate |
Return Type: Boolean
Examples: Given that the “abc” attribute contains the value “hello world”, “xyz” contains “good bye world”, and “filename” contains “file.txt” consider the following examples:
| Expression | Value |
|---|---|
${anyAttribute("abc", "xyz"):contains("bye")} | true |
${anyAttribute("filename","xyz"):toUpper():contains("e")} | false |
Description: Checks to see if all of the given attributes match the given condition. This function has no subject and takes one or more arguments that are the names of attributes to which the remainder of the Expression is to be applied. If all of the attributes specified, when evaluated against the rest of the Expression, returns a value of true, then this function will return true. Otherwise, this function will return false.
Subject Type: No Subject
Arguments:
| Argument | Description |
|---|---|
| Attribute Names | One or more attribute names to evaluate |
Return Type: Boolean
Examples: Given that the “abc” attribute contains the value “hello world”, “xyz” contains “good bye world”, and “filename” contains “file.txt” consider the following examples:
| Expression | Value |
|---|---|
${allAttributes("abc", "xyz"):contains("world")} | true |
${allAttributes("abc", "filename","xyz"):toUpper():contains("e")} | false |
Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are Regular Expressions to match against attribute names. Any attribute whose name matches one of the supplied Regular Expressions will be evaluated against the rest of the Expression. If any of the attributes specified, when evaluated against the rest of the Expression, returns a value of true, then this function will return true. Otherwise, this function will return false.
Subject Type: No Subject
Arguments:
| Argument | Description |
|---|---|
| Regex | One or more Regular Expressions to evaluate against attribute names |
Return Type: Boolean
Examples: Given that the “abc” attribute contains the value “hello world”, “xyz” contains “good bye world”, and “filename” contains “file.txt” consider the following examples:
| Expression | Value |
|---|---|
${anyMatchingAttribute("[ax].*"):contains('bye')} | true |
${anyMatchingAttribute(".*"):isNull()} | false |
Description: Checks to see if any of the given attributes, match the given condition. This function has no subject and takes one or more arguments that are Regular Expressions to match against attribute names. Any attribute whose name matches one of the supplied Regular Expressions will be evaluated against the rest of the Expression. If all of the attributes specified, when evaluated against the rest of the Expression, return a value of true, then this function will return true. Otherwise, this function will return false.
Subject Type: No Subject
Arguments:
| Argument | Description |
|---|---|
| Regex | One or more Regular Expressions to evaluate against attribute names |
Return Type: Boolean
Examples: Given that the “abc” attribute contains the value “hello world”, “xyz” contains “good bye world”, and “filename” contains “file.txt” consider the following examples:
| Expression | Value |
|---|---|
${allMatchingAttributes("[ax].*"):contains("world")} | true |
${allMatchingAttributes(".*"):isNull()} | false |
${allMatchingAttributes("f.*"):count()} | 1 |
Description: Splits a String apart according to a delimiter that is provided, and then evaluates each of the values against the rest of the Expression. If the Expression, when evaluated against any of the individual values, returns true, this function returns true. Otherwise, the function returns false.
Subject Type: No Subject
Arguments:
| Argument | Description |
|---|---|
| Delineated Value | The value that is delineated. This is generally an embedded Expression, though it does not have to be. |
| Delimiter | The value to use to split apart the delineatedValue argument. |
Return Type: Boolean
Examples: Given that the “number_list” attribute contains the value “1,2,3,4,5”, and the “word_list” attribute contains the value “the,and,or,not”, consider the following examples:
| Expression | Value |
|---|---|
${anyDelineatedValue("${number_list}", ","):contains("5")} | true |
${anyDelineatedValue("this that and", ","):equals("${word_list}")} | false |
Description: Splits a String apart according to a delimiter that is provided, and then evaluates each of the values against the rest of the Expression. If the Expression, when evaluated against all of the individual values, returns true in each case, then this function returns true. Otherwise, the function returns false.
Subject Type: No Subject
Arguments:
| Argument | Description |
|---|---|
| Delineated Value | The value that is delineated. This is generally an embedded Expression, though it does not have to be. |
| Delimiter | The value to use to split apart the delineatedValue argument. |
Return Type: Boolean
Examples: Given that the “number_list” attribute contains the value “1,2,3,4,5”, and the “word_list” attribute contains the value “those,known,or,not”, consider the following examples:
| Expression | Value |
|---|---|
${allDelineatedValues("${word_list}", ","):contains("o")} | true |
${allDelineatedValues("${number_list}", ","):count()} | 4 |
${allDelineatedValues("${number_list}", ","):matches("[0-9]+")} | true |
${allDelineatedValues("${word_list}", ","):matches('e')} | false |
Description: Aggregate function that concatenates multiple values with the specified delimiter. This function may be used only in conjunction with the allAttributes, allMatchingAttributes, and allDelineatedValues functions.
Subject Type: String
Arguments:
| Argument | Description |
|---|---|
| Delimiter | The String delimiter to use when joining values |
Return Type: String
Examples: Given that the “abc” attribute contains the value “hello world”, “xyz” contains “good bye world”, and “filename” contains “file.txt” consider the following examples:
| Expression | Value |
|---|---|
${allMatchingAttributes("[ax].*"):substringBefore(" "):join("-")} | hello-good |
${allAttributes("abc", "xyz"):join(" now")} | hello world nowgood bye world now |
Description: Aggregate function that counts the number of non-null, non-false values returned by the allAttributes, allMatchingAttributes, and allDelineatedValues. This function may be used only in conjunction with the allAttributes, allMatchingAttributes, and allDelineatedValues functions.
Subject Type: Any
Arguments: No arguments
Return Type: Number
Examples: Given that the “abc” attribute contains the value “hello world”, “xyz” contains “good bye world”, and “number_list” contains “1,2,3,4,5” consider the following examples:
| Expression | Value |
|---|---|
${allMatchingAttributes("[ax].*"):substringBefore(" "):count()} | 2 |
${allAttributes("abc", "xyz"):contains("world"):count()} | 1 |
${allDelineatedValues(${number_list}, ","):count()} | 5 |
${allAttributes("abc", "non-existent-attr", "xyz"):count()} | 2 |
${allMatchingAttributes(".*"):length():gt(10):count()} | 2 |
Description: Formats a number as a date/time according to the format specified by the argument. The argument must be a String that is a valid strftime format. The Subject is expected to be a Number that represents the number of milliseconds since Midnight GMT on January 1, 1970. The number will be evaluated using the local time zone unless specified in the second optional argument.
Subject Type: Number
Arguments:
| Argument | Description |
|---|---|
| format | The format to use in the strftime syntax |
| time zone | Optional argument that specifies the time zone to use from the IANA Time Zone Database (e.g. ‘America/New_York’) |
Return Type: String
Examples:
If the attribute “time” has the value “1420058163264”, then the following Expressions will yield the following results:
| Expression | Value |
|---|---|
${time:format("%Y/%m/%d %H:%M:%S", "GMT")} | 2014/12/31 20:36:03 |
${time:format("%Y", "America/Los_Angeles")} | 2014 |
Description: Converts a String into a date represented by the number of milliseconds since the UNIX epoch, based on the format specified by the argument. The argument must be a String that is a valid strftime syntax. The Subject is expected to be a String that is formatted according the argument. The date will be evaluated using the local time zone unless specified in the second optional argument.
Subject Type: String
| format | The format to use in the strftime syntax | | time zone | Optional argument that specifies the time zone to use when parsing the subject, from the IANA Time Zone Database (e.g. ‘America/New_York’) |
Return Type: Number
Examples:
If the attribute “year” has the value “2014” and the attribute “time” has the value “2014/12/31 15:36:03.264Z”, then the Expression ${year:toDate('%Y', 'GMT')} will return a date with a value representing Midnight GMT on January 1, 2014. The Expression `${time:toDate(“%Y/%m/%d %H:%M:%S”, “GMT”)} will result in a date for 15:36:03 GMT on December 31, 2014.
Often, this function is used in conjunction with the format function to change the format of a date/time. For example, if the attribute “date” has the value “12-24-2014” and we want to change the format to “2014/12/24”, we can do so by chaining together the two functions: ${date:toDate('%m-%d-%Y'):format('%Y/%m/%d')}.
Description: Returns the current date and time as a Date data type object.
Subject Type: String
Arguments: No arguments
Return Type: Number
Examples:
| Expression | Value |
|---|---|
${now()} | Count of milliseconds since the UNIX epoch |
${now():minus(86400000) | A number presenting the time 24 hours ago |
${now():format('Y')} | The current year |
${now():minus(86400000):format('%a')} | The day of the week that was yesterday, as a 3-letter abbreviation (For example, Wed) |