LambdaMetafactory的Java访问bean方法
发布时间:2020-12-15 07:38:29 所属栏目:Java 来源:网络整理
导读:我的问题与 Explicit use of LambdaMetafactory密切相关 在该线程中,提供了一些非常好的示例来使用LambdaMetafactory来访问类的静态方法;但是,我想知道访问现有bean实例的非静态字段的等效代码是什么.似乎很难找到一个例子,我所执行的每一次尝试都以非工作代
我的问题与
Explicit use of LambdaMetafactory密切相关
在该线程中,提供了一些非常好的示例来使用LambdaMetafactory来访问类的静态方法;但是,我想知道访问现有bean实例的非静态字段的等效代码是什么.似乎很难找到一个例子,我所执行的每一次尝试都以非工作代码结束. 这是bean代码: class SimpleBean { private Object obj= "myCustomObject"; private static Object STATIC_OBJECT = "myCustomStaticObject"; public Object getObj() { return obj; } public void setObj(final Object obj) { this.obj = obj; } public static Object getStaticObj() { return STATIC_OBJECT; } public static void setStaticObj(final Object obj) { STATIC_OBJECT = obj; } } 这里是一个成功访问静态方法“getStaticObj()”的工作单元测试: @Test public void accessStaticMethod() throws Throwable { MethodHandles.Lookup caller = MethodHandles.lookup(); Method reflected = SimpleBean.class.getDeclaredMethod("getStaticObj"); MethodHandle methodHandle = caller.unreflect(reflected); CallSite site = LambdaMetafactory.metafactory(caller,"get",MethodType.methodType(Supplier.class),MethodType.methodType(Object.class),methodHandle,MethodType.methodType(Object.class)); MethodHandle factory = site.getTarget(); Supplier r = (Supplier) factory.invoke(); assertEquals( "myCustomStaticObject",r.get()); } 现在,我尝试访问非静态“getObj()”方法失败: @Test public void accessNonStaticMethodTestOne() throws Throwable { SimpleBean simpleBeanInstance = new SimpleBean(); MethodHandles.Lookup caller = MethodHandles.lookup(); MethodHandle methodHandle = caller.bind(simpleBeanInstance,"getObj",MethodType.methodType(Object.class)); assertEquals("myCustomObject",methodHandle.invoke()); // This test fails here with exception: // java.lang.IllegalArgumentException: not a direct method handle CallSite site = LambdaMetafactory.metafactory(caller,MethodType.methodType(Object.class)); MethodHandle factory = site.getTarget(); Supplier r = (Supplier) factory.invoke(); assertEquals( "myCustomObject",r.get()); } @Test public void accessNonStaticMethodTwo() throws Throwable { SimpleBean simpleBeanInstance = new SimpleBean(); MethodHandles.Lookup caller = MethodHandles.lookup(); Method reflected = SimpleBean.class.getDeclaredMethod("getObj"); MethodHandle methodHandle = caller.unreflect(reflected); // This test fails here with exception: // java.lang.invoke.LambdaConversionException: Incorrect number of parameters CallSite site = LambdaMetafactory.metafactory(caller,MethodType.methodType(Object.class)); MethodHandle factory = site.getTarget(); factory = factory.bindTo(simpleBeanInstance); Supplier r = (Supplier) factory.invoke(); assertEquals( "myCustomObject",r.get()); } @Test public void accessNonStaticMethodThree() throws Throwable { SimpleBean simpleBeanInstance = new SimpleBean(); MethodHandles.Lookup caller = MethodHandles.lookup(); Method reflected = SimpleBean.class.getDeclaredMethod("getObj"); MethodHandle methodHandle = caller.unreflect(reflected); CallSite site = LambdaMetafactory.metafactory(caller,MethodType.methodType(Object.class,SimpleBean.class),SimpleBean.class)); MethodHandle factory = site.getTarget(); //This test fails here with exception: // java.lang.IllegalArgumentException: no leading reference parameter: spike.LambdaBeanAccessAtRuntimeTest$SimpleBean@4459eb14 factory = factory.bindTo(simpleBeanInstance); Supplier r = (Supplier) factory.invoke(); assertEquals( "myCustomObject",r.get()); } 每次尝试都有不同的负面结果,我真的希望有人帮助我让至少一项测试工作正常. 解决方法
如果要将值绑定到lamba,则必须将这些参数包含在invokedtype签名中:
SimpleBean simpleBeanInstance = new SimpleBean(); MethodHandles.Lookup caller = MethodHandles.lookup(); MethodType getter=MethodType.methodType(Object.class); MethodHandle target=caller.findVirtual(SimpleBean.class,getter); CallSite site = LambdaMetafactory.metafactory(caller,// include types of the values to bind: MethodType.methodType(Supplier.class,getter,target,getter); MethodHandle factory = site.getTarget(); factory = factory.bindTo(simpleBeanInstance); Supplier r = (Supplier) factory.invoke(); assertEquals( "myCustomObject",r.get()); 您可以使用以bean作为参数的Function,而不是绑定值: SimpleBean simpleBeanInstance = new SimpleBean(); MethodHandles.Lookup caller = MethodHandles.lookup(); MethodType getter=MethodType.methodType(Object.class); MethodHandle target=caller.findVirtual(SimpleBean.class,getter); MethodType func=target.type(); CallSite site = LambdaMetafactory.metafactory(caller,"apply",MethodType.methodType(Function.class),func.generic(),func); MethodHandle factory = site.getTarget(); Function r = (Function)factory.invoke(); assertEquals( "myCustomObject",r.apply(simpleBeanInstance)); (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |