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AOP或APT,用于重写超类中的方法

apt aspectj wicket code-generation java

Sean Patrick Floyd · 技术社区 · 14 年前

我有一个用自定义注释注释的wicket组件的大型库 @ReferencedResource @ReferencedResources ,有一个 ReferencedResouce[] value() 参数以允许多个批注。

下面是一个示例代码段:

@ReferencedResources({
    @ReferencedResource(value = Libraries.MOO_TOOLS, type = ResourceType.JAVASCRIPT),
    @ReferencedResource(value = "behaviors/promoteSelectOptions", type = ResourceType.JAVASCRIPT) })
public class PromoteSelectOptionsBehavior extends AbstractBehavior{
 ...
}

apt

@ReferencedResource(value = "behaviors/promoteSelectOptions",
                     type = ResourceType.JAVASCRIPT)

将导致编译失败,除非 js/behaviors/promoteSelectOptions.js 可以在类路径上找到。这部分很好用。

现在我也是DRY的粉丝,我希望在创建对象时使用相同的注释将资源注入到对象中。使用AspectJ,我实现了其中的一部分。

带注释的对象总是 Component 或 AbstractBehavior

对于组件,事情很简单,只需在构造函数之后匹配即可。以下是一条建议:

pointcut singleAnnotation() : @within(ReferencedResource);

pointcut multiAnnotation() : @within(ReferencedResources);

after() : execution(Component+.new(..)) && (singleAnnotation() || multiAnnotation()){
    final Component component = (Component) thisJoinPoint.getTarget();
    final Collection<ReferencedResource> resourceAnnotations =
        // gather annotations from cache
        this.getResourceAnnotations(component.getClass());
    for(final ReferencedResource annotation : resourceAnnotations){
        // helper utility that handles the creation of statements like
        // component.add(JavascriptPackageResource.getHeaderContribution(path))
        this.resourceInjector.inject(component, annotation);
    }
}

但是对于行为,我需要将资源附加到响应,而不是行为本身。以下是我使用的切入点:

pointcut renderHead(IHeaderResponse response) :
    execution(* org.apache.wicket.behavior.AbstractBehavior+.renderHead(*))
        && args(response);

before(final IHeaderResponse response) : 
    renderHead(response) && (multiAnnotation() || singleAnnotation()) {
    final Collection<ReferencedResource> resourceAnnotations =
        this.getResourceAnnotations(thisJoinPoint.getTarget().getClass());
    for(final ReferencedResource resource : resourceAnnotations){
        this.resourceInjector.inject(response, resource);
    }
}

如果类重写 renderHead(response) 方法,但在许多情况下这并不是必需的,因为一个超类已经实现了基类功能,而子类只添加了一些配置。因此,一种解决方案是让这些类定义如下方法:

@Override
public void renderHead(IHeaderResponse response){
    super.renderHead(response);
}

我已经使用APT和sunjavac调用创建了一个有效的解决方案。但是,这会导致下一个问题: Running APT and AspectJ in the same project using maven .

1 回复 | 直到 7 年前

Sean Patrick Floyd 14 年前

回答我自己的问题:

这些字段都在中初始化 init(env) process(annotations, roundEnv) :

private static Filer filer;
private static JavacProcessingEnvironment environment;
private static Messager messager;
private static Types types;
private static JavacElements elementUtils;
private Trees trees;
private TreeMaker treeMaker;
private IdentityHashMap<JCCompilationUnit, Void> compilationUnits;
private Map<String, JCCompilationUnit> typeMap;

这就是所谓的逻辑,如果 AbstractBehavior 具有注释的不重写 renderHead(response) 方法:

private void addMissingSuperCall(final TypeElement element){
    final String className = element.getQualifiedName().toString();
    final JCClassDecl classDeclaration =
        // look up class declaration from a local map 
        this.findClassDeclarationForName(className);
    if(classDeclaration == null){
        this.error(element, "Can't find class declaration for " + className);
    } else{
        this.info(element, "Creating renderHead(response) method");
        final JCTree extending = classDeclaration.extending;
        if(extending != null){
            final String p = extending.toString();
            if(p.startsWith("com.myclient")){
                // leave it alone, we'll edit the super class instead, if
                // necessary
                return;
            } else{
                // @formatter:off (turns off eclipse formatter if configured)

                // define method parameter name
                final com.sun.tools.javac.util.Name paramName =
                    elementUtils.getName("response");
                // Create @Override annotation
                final JCAnnotation overrideAnnotation =
                    this.treeMaker.Annotation(
                        Processor.buildTypeExpressionForClass(
                            this.treeMaker,
                            elementUtils,
                            Override.class
                        ),
                        // with no annotation parameters
                        List.<JCExpression> nil()
                    );
                // public
                final JCModifiers mods =
                    this.treeMaker.Modifiers(Flags.PUBLIC,
                        List.of(overrideAnnotation));
                // parameters:(final IHeaderResponse response)
                final List<JCVariableDecl> params =
                    List.of(this.treeMaker.VarDef(this.treeMaker.Modifiers(Flags.FINAL),
                        paramName,
                        Processor.buildTypeExpressionForClass(this.treeMaker,
                            elementUtils,
                            IHeaderResponse.class),
                        null));

                //method return type: void
                final JCExpression returnType =
                    this.treeMaker.TypeIdent(TypeTags.VOID);


                // super.renderHead(response);
                final List<JCStatement> statements =
                    List.<JCStatement> of(
                        // Execute this:
                        this.treeMaker.Exec(
                            // Create a Method call:
                            this.treeMaker.Apply(
                                // (no generic type arguments)
                                List.<JCExpression> nil(),
                                // super.renderHead
                                this.treeMaker.Select(
                                    this.treeMaker.Ident(
                                        elementUtils.getName("super")
                                    ),
                                    elementUtils.getName("renderHead")
                                ),
                                // (response)
                                List.<JCExpression> of(this.treeMaker.Ident(paramName)))
                            )
                     );
                // build code block from statements
                final JCBlock body = this.treeMaker.Block(0, statements);
                // build method
                final JCMethodDecl methodDef =
                    this.treeMaker.MethodDef(
                        // public
                        mods,
                        // renderHead
                        elementUtils.getName("renderHead"),
                        // void
                        returnType,
                        // <no generic parameters>
                        List.<JCTypeParameter> nil(),
                        // (final IHeaderResponse response)
                        params,
                        // <no declared exceptions>
                        List.<JCExpression> nil(),
                        // super.renderHead(response);
                        body,
                        // <no default value>
                        null);

                // add this method to the class tree
                classDeclaration.defs =
                    classDeclaration.defs.append(methodDef);

                // @formatter:on turn eclipse formatter on again
                this.info(element,
                    "Created renderHead(response) method successfully");

            }
        }

    }
}