Java8从类中检索lambda setter
我正在尝试为私有字段的setter获取lambda方法句柄,但由于某种原因,无法找到setter。
这是我正在使用的function界面:
@FunctionalInterface public interface ISetter { void set(T object, R value); }
这是用于获取setter的方法:
public ISetter getSetter(Class clazz, String fieldName, Class fieldType) throws Throwable { MethodHandles.Lookup caller = MethodHandles.lookup(); MethodType setter = MethodType.methodType(Void.class, fieldType); MethodHandle target = caller.findVirtual(clazz, computeSetterName(fieldName), setter); MethodType func = target.type(); CallSite site = LambdaMetafactory.metafactory( caller, "set", MethodType.methodType(ISetter.class), func.generic(), target, func ); MethodHandle factory = site.getTarget(); ISetter r = (ISetter) factory.invoke(); return r; }
按照惯例,所有setter都命名相同:“setField(…)”。 这是我的测试类:
public class TestEntity { private Long id; public TestEntity(Long id) { this.id = id; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } }
但是当我为“id”和“Long.class”执行此方法时,我得到以下exception:
Exception in thread "main" java.lang.NoSuchMethodException: no such method: de.cyclonit.exercise.TestEntity.setId(Long)Void/invokeVirtual at java.lang.invoke.MemberName.makeAccessException(MemberName.java:871) at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1003) at java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:1381) at java.lang.invoke.MethodHandles$Lookup.findVirtual(MethodHandles.java:859) at de.cyclonit.exercise.AccessorFactory.getSetter(AccessorFactory.java:41) at de.cyclonit.exercise.Main.main(Main.java:21) Caused by: java.lang.NoSuchFieldError: method resolution failed at java.lang.invoke.MethodHandleNatives.resolve(Native Method) at java.lang.invoke.MemberName$Factory.resolve(MemberName.java:975) at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1000) ... 4 more
我不明白这个错误来自哪里。 方法“void setId(Long)”确实存在。
public String computeSetterName(String fieldName) { return "set" + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1); }
电话:
ISetter setter = accessorFactory.getSetter(TestEntity.class, "id", Long.class);
您的代码中存在一些错误。
首先,您使用的是Void.class
,您应该使用void.class
。
其次, func.generic
返回(Object,Object)Object
,你真正想要的是func.erase
,所以返回类型被保留( (Object,Object)void
)。
第三,建议不使用原始类型,我建议改为:
public static ISetter getSetter(Class clazz, String fieldName, Class fieldType) throws Throwable { MethodHandles.Lookup caller = MethodHandles.lookup(); MethodType setter = MethodType.methodType(void.class, fieldType); MethodHandle target = caller.findVirtual(clazz, computeSetterName(fieldName), setter); MethodType func = target.type(); CallSite site = LambdaMetafactory.metafactory( caller, "set", MethodType.methodType(ISetter.class), func.erase(), target, func ); MethodHandle factory = site.getTarget(); ISetter r = (ISetter) factory.invoke(); return r; }
哪个适合我: http : //ideone.com/KKx10r