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| </div><div id='content' class='page-1'><div class='row'><div class='row-fluid'><div class='col-lg-3'><ul class='nav-sidebar'><li><a href='./'>Blog index</a></li><li class='active'><a href='#doc'>Groovy Records</a></li><li><a href='#_introduction' class='anchor-link'>Introduction</a></li><li><a href='#_optional_enhancements' class='anchor-link'>Optional enhancements</a></li><li><a href='#_internal_details' class='anchor-link'>Internal details</a></li><li><a href='#_declarative_customisation_of_records' class='anchor-link'>Declarative customisation of records</a></li><li><a href='#_emulated_records' class='anchor-link'>Emulated records</a></li><li><a href='#_using_records_with_other_ast_transforms' class='anchor-link'>Using records with other AST transforms</a></li><li><a href='#_related_functionality_for_reducing_boilerplate_code' class='anchor-link'>Related functionality for reducing boilerplate code</a></li><li><a href='#_summary' class='anchor-link'>Summary</a></li></ul><br/><ul class='nav-sidebar'><li style='padding: 0.35em 0.625em; background-color: #eee'><span>Related posts</span></li><li><a href='./deep-learning-and-eclipse-collections'>Deep Learning and Eclipse Collections</a></li><li><a href='./comparators-and-sorting-in-groovy'>Comparators and Sorting in Groovy</a></li><li><a href='./deck-of-cards-with-groovy'>Deck of cards with Groovy, JDK collections and Eclipse Collections</a></li><li><a href='./reading-and-writing-csv-files'>Reading and Writing CSV files with Groovy</a></li><li><a href='./using-groovy-with-apache-wayang'>Using Groovy with Apache Wayang and Apache Spark</a></li></ul></div><div class='col-lg-8 col-lg-pull-0'><a name='doc'></a><h1>Groovy Records</h1><p><span>Author: <i>Paul King</i></span><br/><span>Published: 2023-04-02 08:22PM</span></p><hr/><div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>A common scenario when programming is the need to group together a bunch |
| of related properties. You may be able to use arrays, some form of tuples, or maps |
| to group such properties. Some languages might support constructs like structs. |
| In Java, grouping such properties into a class is a natural fit. |
| Unfortunately, creating such classes, once you add in all the expected |
| methods and behaviors, can involve considerable boilerplate code.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Starting with JDK16 (with previews from JDK14), Java introduced <em>records</em> as a compact |
| form for declaring "<em>data</em>" classes. Such classes hold "data" and (almost) nothing else. |
| Java chose the very common scenario of holding <em>immutable</em> data. |
| With this context, and following a few restrictions, it becomes a relatively easy |
| task for the Java compiler to generate much of the boilerplate for such classes.</p> |
| </div> |
| <div class="paragraph"> |
| <p>This blog looks at Groovy’s record implementation. Groovy supports the |
| same features as Java but adds some additional enhancements and customisation. |
| Groovy’s implementation builds upon existing techniques, like compile-time metaprogramming |
| (aka AST transforms), that are used to reduce boilerplate for other scenarios.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_introduction">Introduction</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>First, let’s look at what creating a record looks like:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">record Point(int x, int y, String color) { }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The properties we are grouping, are called <em>components</em>. |
| In this case two integers, <code>x</code> and <code>y</code>, and a string <code>color</code>.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Using it is similar to how we’d use a traditionally defined <code>Point</code> class |
| which had a constructor with the same parameters as our record definition:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var bluePointAtOrigin = new Point(0, 0, 'Blue')</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>We might want to check the value of one of our point’s components:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert bluePointAtOrigin.color() == 'Blue'</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>We can also print out the point (which calls its <code>toString()</code> method):</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">println bluePointAtOrigin</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Which would have this output:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>Point[x=0, y=0, color=Blue]</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>All the features of Java records are supported. |
| One example is compact constructors. |
| If we wanted the color to not be left blank, we could add a check using |
| the compact constructors form, giving an alternative definition such as:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">record Point(int x, int y, String color) { |
| Point { assert !color.blank } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>More formally, a record is a class that:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Is implicitly final (so can’t be extended)</p> |
| </li> |
| <li> |
| <p>Has a private final field for each component, e.g. <code>color</code></p> |
| </li> |
| <li> |
| <p>Has an accessor method for each component of the same name, e.g. <code>color()</code></p> |
| </li> |
| <li> |
| <p>Has a default <code>Point(int, int, String)</code> constructor</p> |
| </li> |
| <li> |
| <p>Has a default serialVersionUID of <code>0L</code> and special serialization code</p> |
| </li> |
| <li> |
| <p>Has implicit <code>toString()</code>, <code>equals()</code> and <code>hashCode()</code> methods</p> |
| </li> |
| <li> |
| <p>Implicitly extends the <code>java.lang.Record</code> class (so can’t extend |
| another class but may implement one or more interfaces)</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_optional_enhancements">Optional enhancements</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Groovy records by default have an additional named-argument style constructor:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var greenPointAtOrigin = new Point(x:0, y:0, color:'Green')</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>By default, Groovy records also have generated <code>getAt</code>, <code>size</code>, <code>toList</code>, and |
| <code>toMap</code> methods. The <code>getAt</code> method provides Groovy’s normal array-like indexing. |
| The <code>size</code> method returns the number of components. |
| The <code>toList</code> method returns the component values. |
| The <code>toMap</code> method returns the component values along with the component name. |
| Here are examples:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert bluePointAtOrigin.size() == 3 |
| assert bluePointAtOrigin[2] == 'Blue' |
| assert bluePointAtOrigin.toList() == [0, 0, 'Blue'] |
| assert bluePointAtOrigin.toMap() == [x:0, y:0, color:'Blue']</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>getAt</code> method also enables destructuring through the multi-assignment |
| statement as this example shows:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">def (x, y, c) = bluePointAtOrigin |
| assert "$x $y $c" == '0 0 Blue'</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Shortly, we’ll look at <code>copyWith</code> which is useful for creating one record from another |
| record of the same type. The <code>toMap</code> can be handy when creating a record from a different type as shown here. In our example, we surmise that in the same month as realising a book, |
| we might want to release an article about the book for marketing purposes:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">record Book(String name, String author, YearMonth published) {} |
| |
| record Article(String name, String author, YearMonth published, String publisher) {} |
| |
| def b = new Book('Groovy in Action', 'Dierk & Paul', YearMonth.of(2015, 06)) |
| def a = new Article(*:b.toMap(), publisher: 'InfoQ')</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>These optional enhancements can be turned off if not required by setting |
| various annotation attributes of the same name to <code>false</code> on the <code>RecordOptions</code> annotation.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Two other methods, <code>copyWith</code> and <code>components</code>, aren’t enabled by default |
| but can be enabled by setting the respectively named annotation attributes to <code>true</code> |
| as shown here:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@RecordOptions(components = true, copyWith = true) |
| record Point(int x, int y, String color) { }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>copyWith</code> method can be used as follows:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var redPointAtOrigin = bluePointAtOrigin.copyWith(color: 'Red') |
| assert redPointAtOrigin.toString() == 'Point[x=0, y=0, color=Red]'</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>This is similar to Kotlin’s <code>copy</code> method for data classes.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>components</code> method returns a typed tuple. This is especially useful |
| when type checking is enabled like in this method:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@TypeChecked |
| String description(Point p) { |
| p.components().with{ "${v3.toUpperCase()} point at ($v1,$v2)" } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Note that the 3rd element in the tuple has type <code>String</code>, |
| so we can call the <code>toUpperCase</code> method.</p> |
| </div> |
| <div class="paragraph"> |
| <p>We can use this method as follows:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert description(redPointAtOrigin) == 'RED point at (0,0)'</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>This is Groovy’s equivalent to Kotlin’s <code>componentN</code> methods for data classes.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_internal_details">Internal details</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Some of the details in this section aren’t essential to know |
| but can be useful to understand how to customise record definitions.</p> |
| </div> |
| <div class="paragraph"> |
| <p>When we write a record declaration like this:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">record Point(int x, int y, String color) { }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>It is equivalent to the following traditional declaration:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@RecordType |
| class Point { |
| int x |
| int y |
| String color |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>You will almost never write records in this form but if you have some legacy tools |
| which don’t yet understand record syntax, it might prove useful.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>RecordType</code> annotation is what is known as a meta-annotation (also sometimes called |
| an annotation collector). This means that it is an annotation made of other annotations. |
| Without going into the details, essentially, the compiler expands the above annotation |
| into the following (and <code>RecordBase</code> further calls into <code>ToString</code> and <code>EqualsAndHashCode</code>):</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@RecordBase |
| @RecordOptions |
| @TupleConstructor(namedVariant = true, force = true, defaultsMode = AUTO) |
| @PropertyOptions |
| @KnownImmutable |
| @POJO |
| @CompileStatic |
| class Point { |
| int x |
| int y |
| String color |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>What this means is that if you don’t like the generated code you would normally |
| get with a record, you have several places where you can change |
| the behavior in a declarative fashion. We’ll cover that next.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Just be careful though, if you are creating a native record and try to change |
| something that would violate the JDKs assumptions about records, |
| you will likely get a compiler error.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_declarative_customisation_of_records">Declarative customisation of records</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>We looked earlier at ensuring that we don’t provide an empty <code>color</code> |
| by using the compact constructor form. We have several other alternatives |
| we could use. If we want to check that <code>color</code> isn’t null or the empty |
| string, we could use:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@TupleConstructor(pre={ assert color }) |
| record Point(int x, int y, String color) { }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Or, to also rule out a color of only blank spaces, and also disable the |
| named-argument style constructor, we could use:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@TupleConstructor(pre={ assert color && !color.blank }, namedVariant=false) |
| record Point(int x, int y, String color) { }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>We can also change the <code>toString()</code> method with a declarative style:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@ToString(excludes = 'color', cache = true) |
| record Point(int x, int y, String color) { } |
| assert new Point(0, 0, 'Gold').toString() == 'Point(0, 0)'</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Here we are excluding the <code>color</code> component from the toString value |
| and also caching the result for subsequent calls to toString.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_emulated_records">Emulated records</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Groovy also provides emulated records for JDK8+. |
| Emulated records are classes that don’t include a record attribute in the class file, |
| nor offer special record serialization, nor extend the <code>java.lang.Record</code> |
| class, but will follow all the other record conventions. This means that |
| you can use the <code>record</code> shorthand even if you are still stuck on JDK8 or JDK11.</p> |
| </div> |
| <div class="paragraph"> |
| <p>By default, emulated records are provided for JDK8-15 and |
| native records for JDK16+. You can force the compiler to |
| always target emulated or native records using the <code>mode</code> |
| annotation attribute of <code>RecordOptions</code>. If you specify the |
| <code>NATIVE</code> mode and are on an earlier JDK or are targeting |
| an earlier bytecode version, you will receive a compiler error.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_using_records_with_other_ast_transforms">Using records with other AST transforms</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>We saw that we could customize the generated code by using variations of |
| the annotations which make up the <code>RecordType</code> meta-annotation. |
| We can also use most of the normal AST transforms available in Groovy. |
| Here are just a few examples:</p> |
| </div> |
| <div class="paragraph"> |
| <p>We saw earlier a <code>description</code> method that took a <code>Point</code> as parameter. |
| While we generally want records to be data only, that’s the kind of method that |
| makes sense to place inside the record. We can do so as follows and make use of |
| <code>Memoized</code> to cache the result:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">record Point(int x, int y, String color) { |
| @Memoized |
| String description() { |
| "${color.toUpperCase()} point at ($x,$y)" |
| } |
| } |
| |
| var pinkPointAtOrigin = new Point(x:0, y:0, color:'Pink') |
| assert pinkPointAtOrigin.description() == 'PINK point at (0,0)'</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>We have also yet another way to check for blank colors by using |
| the design-by-contract functionality of <code>groovy-contracts</code>:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@Requires({ color && !color.blank }) |
| record Point(int x, int y, String color) { }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>We can also make records which are easily sortable as follows:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">@Sortable |
| record Point(int x, int y, String color) { } |
| |
| var points = [ |
| new Point(0, 100, 'red'), |
| new Point(10, 10, 'blue'), |
| new Point(100, 0, 'green'), |
| ] |
| |
| println points.toSorted(Point.comparatorByX()) |
| println points.toSorted(Point.comparatorByY()) |
| println points.toSorted(Point.comparatorByColor())</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Which has this output:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>[Point[x=0, y=100, color=red], Point[x=10, y=10, color=blue], Point[x=100, y=0, color=green]] |
| [Point[x=100, y=0, color=green], Point[x=10, y=10, color=blue], Point[x=0, y=100, color=red]] |
| [Point[x=10, y=10, color=blue], Point[x=100, y=0, color=green], Point[x=0, y=100, color=red]]</pre> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_related_functionality_for_reducing_boilerplate_code">Related functionality for reducing boilerplate code</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>While records represent a big jump in reducing boilerplate in the Java world, |
| we should point out the Groovy has many features for reducing boilerplate |
| beyond just records. Groovy already has a feature very much like records, |
| the <code>@Immutable</code> transform. This offers much of the boilerplate reduction |
| of records but follows JavaBean conventions.</p> |
| </div> |
| <div class="paragraph"> |
| <p>If you don’t want immutability, you can use <code>@Canonical</code>, or you can just |
| mix in the appropriate transforms from <code>@ToString</code>, <code>@EqualsAndHashCode</code>, |
| <code>@TupleConstructor</code>, <code>@MapConstructor</code> and so forth.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Here is a summary of the main transforms and the provided functionality:</p> |
| </div> |
| <div class="paragraph"> |
| <p><span class="image"><img src="img/record_like_functionality.png" alt="record like functionality"></span></p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_summary">Summary</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Let’s wrap up our introduction to records with a summary of functionality:</p> |
| </div> |
| <div class="paragraph"> |
| <p><span class="image"><img src="img/record_feature_summary.png" alt="TodoScreenshot"></span></p> |
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