View Javadoc
1   /*
2    * Copyright (c) MuleSoft, Inc.  All rights reserved.  http://www.mulesoft.com
3    * The software in this package is published under the terms of the CPAL v1.0
4    * license, a copy of which has been included with this distribution in the
5    * LICENSE.txt file.
6    */
7   package org.mule.api.annotations;
8   
9   import java.lang.annotation.Documented;
10  import java.lang.annotation.ElementType;
11  import java.lang.annotation.Retention;
12  import java.lang.annotation.RetentionPolicy;
13  import java.lang.annotation.Target;
14  
15  /**
16   * Used to mark a that a class contains methods which are Mule Transformer, which means it will be made available in the Mule container.
17   * Transformers are used to convert one object type to another.  Mule uses them to provide automatic conversion of Java types
18   * and now support Mime type conversion too.
19   *
20   * The parameters passed into the method define the source object(s) to transform, the return type of the method defines the return object type.
21   * Transformers can define additional source types, that when received will be automatically converted to the parameter type accepted by
22   * the annotated method.
23   *
24   * There are some rules to follow when writing a transformer method -
25   * <ol>
26   * <li>The method's declaring class must be annotated with ContainsTransformerMethods</li>
27   * <li>The annotation must appear on a concrete method, not on an abstract or interface method</li>
28   * <li>The method must be public</li>
29   * <li>The method must have a non-void return type</li>
30   * <li>The method must have at least one parameter argument</li>
31   * </ol>
32   *
33   * It is good practice to define any custom transformers in their own class (a class can have more than one transformer method).
34   * A transformer class should be thread-safe and not have any transitive state, meaning that it should not maintain state as
35   * a result of a transformation. It is fine for transformers to have configuration state, such as in an XSLT or XQuery template file
36   * (note that Mule already provides transformers for XSLT and XQuery).
37   */
38  @Target(ElementType.METHOD)
39  @Retention(RetentionPolicy.RUNTIME)
40  @Documented
41  public @interface Transformer
42  {
43      /**
44       * The 'priorityWeighting property is used to resolve conflicts where there is more than one transformers that match
45       * the selection criteria.  10 is the highest priority and 1 is the lowest.
46       *
47       * @return the priority weighting for this transformer. If the class defines more than one transform method, every transform
48       *         method will have the same weighting.
49       */
50      int priorityWeighting() default 5;
51  
52      //TODO BL-140 add when we get support for Transformer mime types
53  //    String sourceMimeType() default MimeTypes.ANY;
54  //
55  //    String resultMimeType() default MimeTypes.ANY;
56  
57      /**
58       * SourceTypes define additional types that this transformer will accepts as a sourceType (beyond the method parameter).
59       * At run time if the current message matches one of these source types, Mule will attempt to transform from
60       * the source type to the method parameter type.  This means that transformations can be chained. The user can create
61       * other transformers to be a part of this chain.
62       *
63       * @return an array of class types which allow the transformer to be matched on
64       */
65      Class[] sourceTypes() default {};
66  }