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| |
| <body> |
| Use Java reflection to generate schemas and protocols for existing |
| classes. |
| |
| <p>Java types are mapped to Avro schemas as follows: |
| |
| <ul> |
| |
| <li><b>Classes</b> are mapped to Avro records. Only concrete classes |
| with a no-argument constructor are supported. All inherited fields |
| that are not static or transient are used. Fields are not permitted |
| to be null unless annotated by {@link |
| org.apache.avro.reflect.Nullable Nullable} or a {@link |
| org.apache.avro.reflect.Union Union} containing {@link java.lang.Void}.</li> |
| |
| <li><b>Arrays</b> are mapped to Avro array schemas. If an array's |
| elements are a union defined by the {@link |
| org.apache.avro.reflect.Union Union} annotation, the "java-element" |
| property is set to the union's class, e.g.: |
| <pre>{"type": "array", "java-element": "org.acme.Foo"}</pre> |
| </li> |
| |
| <li><b>Collection</b> implementations are mapped to Avro array schemas |
| with the "java-class" property set to the collection |
| implementation, e.g.: |
| <pre>{"type": "array", "java-class": "java.util.ArrayList"}</pre> |
| </li> |
| |
| <li><b>{@link java.lang.String}</b> is mapped to an Avro string schema.</li> |
| |
| <li><b>byte[]</b> is mapped to an Avro bytes schema.</li> |
| |
| <li><b>short</b> is mapped to an Avro int schema with the "java-class" |
| property set to "java.lang.Short", e.g.: |
| <pre>{"type": "int", "java-class": "java.lang.Short"}</pre> |
| |
| <li><b>{@link java.math.BigDecimal}, {@link java.math.BigInteger}, |
| {@link java.net.URI}, {@link java.net.URL}, {@link java.io.File}</b> |
| are mapped to an Avro string schema as |
| {@link org.apache.avro.reflect.Stringable Stringable} types and |
| serialized via their {@link java.lang.Object#toString() toString} |
| method and de-serialized via their {@link java.lang.String} constructor. |
| This is done via the "java-class", "java-key-class" or |
| "java-element-class" depending on whether it is a field, or map key |
| or a list/map element, e.g.: |
| <pre>{"type": "string", "java-class": "java.math.BigDecimal"}</pre></li> |
| |
| <li>All other types are mapped as in the {@link org.apache.avro.generic |
| generic} API.</li> |
| |
| </ul> |
| |
| <p>The {@link org.apache.avro.reflect.Union Union} annotation can be used |
| to support reflection of schemas for interfaces, abstract base classes |
| and other uses of polymorphism. |
| |
| <p>The {@link org.apache.avro.reflect.Stringable Stringable} annotation |
| will cause a type to be serialized via its {@link java.lang.Object#toString() |
| toString} method. |
| |
| <p>Fields annotated with {@link org.apache.avro.reflect.AvroIgnore AvroIgnore} |
| will not be written or read to. |
| |
| <p> The {@link org.apache.avro.reflect.AvroName AvroName} annotation renames |
| the field in the schema to the given name. The reflect datum reader will look |
| for a schema field with the given name, when trying to read into such an |
| annotated java field. |
| |
| <p>The {@link org.apache.avro.reflect.AvroMeta AvroMeta} annotation adds an |
| arbitrary key:value pair in the schema at the node of the java field. |
| |
| <p>The {@link org.apache.avro.reflect.AvroSchema AvroSchema} annotation forces |
| the use of an custom schema. |
| |
| <p>The {@link org.apache.avro.reflect.AvroEncode AvroEncode} annotation forces |
| the use of an custom encoder. This annotation overrides |
| {@link org.apache.avro.reflect.Stringable Stringable} and |
| {@link org.apache.avro.reflect.Nullable Nullable}. |
| |
| |
| </body> |
| </html> |
