Chapter 47. Configuring the API Component Maven Plug-In

The main purpose of the API component Maven plug-in, camel-api-component-maven-plugin, is to generate the API mapping classes, which implement the mapping between endpoint URIs and API method invocations. By editing the configuration of the API component Maven plug-in, you can customize various aspects of the API mapping.

The API mapping classes generated by the API component Maven plug-in are placed in the following location, by default:

ProjectName-component/target/generated-sources/camel-component

The main inputs to the API component Maven plug-in are the Java API classes and the Javadoc metadata. These are made available to the plug-in by declaring them as regular Maven dependencies (where the Javadoc Maven dependencies should be declared with provided scope).

The recommended way to set up the API component Maven plug-in is to generate starting point code using the API component archetype. This generates the default plug-in configuration in the ProjectName-component/pom.xml file, which you can then customize for your project. The main aspects of the plug-in set-up are, as follows:

The following POM file extract shows the base configuration of the API component Maven plug-in, as defined in the Maven pluginManagement scope when the code has been generated using the API component archetype:

<?xml version="1.0" encoding="UTF-8"?>
<project ...>
  ...
  <build>
    ...
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.apache.camel</groupId>
          <artifactId>camel-api-component-maven-plugin</artifactId>
          <version>2.21.0.fuse-760027-redhat-00001</version>
          <configuration>
            <scheme>${schemeName}</scheme>
            <componentName>${componentName}</componentName>
            <componentPackage>${componentPackage}</componentPackage>
            <outPackage>${outPackage}</outPackage>
          </configuration>
        </plugin>
      </plugins>
    </pluginManagement>
    ...
  </build>
  ...
</project

The configuration specified in the pluginManagement scope provides default settings for the plug-in. It does not actually create an instance of a plug-in, but its default settings will be used by any API component plug-in instance.

In addition to specifying the plug-in version (in the version element), the preceding base configuration specifies the following configuration properties:

The following POM file extract shows a sample instance of the API component Maven plug-in, which is configured to generate an API mapping during the Maven build:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

  ...
  <build>
    <defaultGoal>install</defaultGoal>

    <plugins>
      ...
      <!-- generate Component source and test source -->
      <plugin>
        <groupId>org.apache.camel</groupId>
        <artifactId>camel-api-component-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>generate-test-component-classes</id>
            <goals>
              <goal>fromApis</goal>
            </goals>
            <configuration>
              <apis>
                <api>
                  <apiName>hello-file</apiName>
                  <proxyClass>org.jboss.fuse.example.api.ExampleFileHello</proxyClass>
                  <fromSignatureFile>signatures/file-sig-api.txt</fromSignatureFile>
                </api>
                <api>
                  <apiName>hello-javadoc</apiName>
                  <proxyClass>org.jboss.fuse.example.api.ExampleJavadocHello</proxyClass>
                  <fromJavadoc/>
                </api>
              </apis>
            </configuration>
          </execution>
        </executions>
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

The plug-in is configured by the configuration element, which contains a single apis child element to configure the classes of the Java API. Each API class is configured by an api element, as follows:

The following aspects of the API mapping can be customized by configuring the plug-in:

It is possible to filter the Javadoc metadata to ignore or explicitly include certain content. For details of how to do this, see Section 47.2, “Javadoc Options”.

In cases where no Javadoc is available, you can resort to signature files to supply the needed mapping metadata. The fromSignatureFile is used to specify the location of the corresponding signature file. It has no special options.

If the metadata for your Java API is provided by Javadoc, it is generally sufficient to specify the fromJavadoc element with no options. But in cases where you do not want to include the entire Java API in your API mapping, you can filter the Javadoc metadata to customize the content. In other words, because the API component Maven plug-in generates the API mapping by iterating over the Javadoc metadata, it is possible to customize the scope of the generated API mapping by filtering out unwanted parts of the Javadoc metadata.

The fromJavadoc element can be configured with optional child elements, as follows:

<fromJavadoc>
  <excludePackages>PackageNamePattern</excludePackages>
  <excludeClasses>ClassNamePattern</excludeClasses>
  <excludeMethods>MethodNamePattern</excludeMethods>
  <includeMethods>MethodNamePattern</includeMethods>
  <includeStaticMethods>[true|false]<includeStaticMethods>
</fromJavadoc>

As shown in the following extract, the fromJavadoc element can optionally appear as a child of the apis element and/or as a child of api elements:

<configuration>
  <apis>
    <api>
      <apiName>...</apiName>
      ...
      <fromJavadoc>...</fromJavadoc>
    </api>
    <fromJavadoc>...</fromJavadoc>
    ...
  </apis>
</configuration>

You can define the fromJavadoc element at the following scopes:

The following options can be defined as child elements of fromJavadoc:

Often it can be useful to define additional names (aliases) for a given method, in addition to the standard method name that appears in the Java API. A particularly common case is where you allow a property name (such as widget) to be used as an alias for an accessor method (such as getWidget or setWidget).

The aliases element can be defined with one or more alias child elements, as follows:

<aliases>
  <alias>
    <methodPattern>MethodPattern</methodPattern>
    <methodAlias>Alias</methodAlias>
  </alias>
  ...
</aliases>

Where MethodPattern is a regular expression (java.util.regex syntax) for matching method names from the Java API, and the pattern typically includes capturing groups. The Alias is the replacement expression (for use in a URI), which can use the text from the preceding capturing groups (for example, specified as $1, $2, or $3 for the text from the first, second, or third capturing group).

As shown in the following extract, the aliases element can optionally appear as a child of the apis element and/or as a child of api elements:

<configuration>
  <apis>
    <api>
      <apiName>...</apiName>
      ...
      <aliases>...</aliases>
    </api>
    <aliases>...</aliases>
    ...
  </apis>
</configuration>

You can define the aliases element at the following scopes:

The following example shows how to generate aliases for the common get/set bean method pattern:

<aliases>
  <alias>
    <methodPattern>[gs]et(.+)</methodPattern>
    <methodAlias>$1</methodAlias>
  </alias>
</aliases>

With the preceding alias definition, you could use widget as an alias for either of the methods getWidget or setWidget. Note the use of a capturing group, (.+), to capture the latter part of the method name (for example, Widget).

In some cases, it can make sense to let method arguments default to null. But this is not allowed by default. If you want to allow some of your method arguments from the Java API to take null values, you must declare this explicitly using the nullableOptions element.

The nullableOptions element can be defined with one or more nullableOption child elements, as follows:

<nullableOptions>
  <nullableOption>ArgumentName</nullableOption>
  ...
</nullableOptions>

Where ArgumentName is the name of a method argument from the Java API.

As shown in the following extract, the nullableOptions element can optionally appear as a child of the apis element and/or as a child of api elements:

<configuration>
  <apis>
    <api>
      <apiName>...</apiName>
      ...
      <nullableOptions>...</nullableOptions>
    </api>
    ...
    <nullableOptions>...</nullableOptions>
  </apis>
</configuration>

You can define the nullableOptions element at the following scopes:

The API component framework requires that URI option names are unique within each proxy class (Java API class). This is not always the case for method argument names, however. For example, consider the following Java methods in an API class:

public void doSomething(int id, String name);
public void doSomethingElse(int id, String name);

When you build your Maven project, the camel-api-component-maven-plugin generates the configuration class, ProxyClassEndpointConfiguration, which contains getter and setter methods for all of the arguments in the ProxyClass class. For example, given the preceding methods, the plug-in would generate the following getter and setter methods in the configuration class:

public int  getId();
public void setId(int id);
public String getName();
public void   setName(String name);

But what happens, if the id argument appears multiple times as different types, as in the following example:

public void doSomething(int id, String name);
public void doSomethingElse(int id, String name);
public String lookupByID(String id);

In this case, the code generation would fail, because you cannot define a getId method that returns int and a getId method that returns String in the same scope. The solution to this problem is to use argument name substitution to customize the mapping of argument names to URI option names.

The substitutions element can be defined with one or more substitution child elements, as follows:

<substitutions>
  <substitution>
    <method>MethodPattern</method>
    <argName>ArgumentNamePattern</argName>
    <argType>TypeNamePattern</argType>
    <replacement>SubstituteArgName</replacement>
    <replaceWithType>[true|false]</replaceWithType>
  </substitution>
  ...
</substitutions>

Where the argType element and the replaceWithType element are optional and can be omitted.

As shown in the following extract, the substitutions element can optionally appear as a child of the apis element and/or as a child of api elements:

<configuration>
  <apis>
    <api>
      <apiName>...</apiName>
      ...
      <substitutions>...</substitutions>
    </api>
    <substitutions>...</substitutions>
    ...
  </apis>
</configuration>

You can define the substitutions element at the following scopes:

Each substitution element can be defined with the following child elements:

The following substitution example modifies every argument of java.lang.String type, by adding the suffix, Param to the argument name:

<substitutions>
  <substitution>
    <method>^.+$</method>
    <argName>^.+$</argName>
    <argType>java.lang.String</argType>
    <replacement>$1Param</replacement>
    <replaceWithType>false</replaceWithType>
  </substitution>
</substitutions>

For example, given the following method signature:

public String greetUs(String name1, String name2);

The arguments of this method would be specified through the options, name1Param and name2Param, in the endpoint URI.

Sometimes, you might need to exclude certain arguments, when it comes to mapping Java arguments to URI options. You can filter out unwanted arguments by specifying either the excludeConfigNames element or the excludeConfigTypes element in the camel-api-component-maven-plugin plug-in configuration.

The excludeConfigNames element and the excludeConfigTypes element are specified as follows:

<excludeConfigNames>ArgumentNamePattern</excludeConfigNames>
<excludeConfigTypes>TypeNamePattern</excludeConfigTypes>

Where ArgumentNamePattern and TypeNamePattern are regular expressions that match the argument name and the argument type, respectively.

As shown in the following extract, the excludeConfigNames element and the excludeConfigTypes element can optionally appear as children of the apis element and/or as children of api elements:

<configuration>
  <apis>
    <api>
      <apiName>...</apiName>
      ...
      <excludeConfigNames>...</excludeConfigNames>
      <excludeConfigTypes>...</excludeConfigTypes>
    </api>
    <excludeConfigNames>...</excludeConfigNames>
    <excludeConfigTypes>...</excludeConfigTypes>
    ...
  </apis>
</configuration>

You can define the excludeConfigNames element and the excludeConfigTypes element at the following scopes:

The following elements can be used to exclude arguments from the API mapping (so that they are unavailable as URI options):

The extraOptions options are usually used to either compute or hide complex API parameters by providing simpler options instead. For example, the API method might take a POJO option, that could be provided more easily as parts of the POJO in the URI. The component could do this by adding the parts as extra options, and creating the POJO parameter internally. To complete the implementation of these extra options, you also need to override the interceptProperties method in the EndpointConsumer and/or EndpointProducer classes (see Section 46.4, “Programming Model”).

The extraOptions element can be defined with one or more extraOption child elements, as follows:

<extraOptions>
  <extraOption>
    <type>TypeName</type>
    <name>OptionName</name>
  </extraOption>
</extraOptions>

Where TypeName is the fully-qualified type name of the extra option and OptionName is the name of the extra URI option.

As shown in the following extract, the extraOptions element can optionally appear as a child of the apis element and/or as a child of api elements:

<configuration>
  <apis>
    <api>
      <apiName>...</apiName>
      ...
      <extraOptions>...</extraOptions>
    </api>
    <extraOptions>...</extraOptions>
    ...
  </apis>
</configuration>

You can define the extraOptions element at the following scopes:

Each extraOptions element can be defined with the following child elements:

The following example defines an extra URI option, customOption, which is of java.util.list<String> type:

<extraOptions>
  <extraOption>
    <type>java.util.List<String></type>
    <name>customOption</name>
  </extraOption>
</extraOptions>