Java8从类中检索lambda setter [英] Java8 retrieving lambda setter from class
问题描述
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,找不到setter。
这是我正在使用的功能接口:
@FunctionalInterface
public interface ISetter< T,R> {
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( ),
目标,
func
);
MethodHandle factory = site.getTarget();
ISetter r =(ISetter)factory.invoke();
返回r;
}
按惯例,所有设置者的名称都相同: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执行此方法时Long.class我得到以下异常:
线程main中的异常java.lang.NoSuchMethodException:没有这样的方法: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)
引起:java.lang.NoSuchFieldError:方法解析失败
at java.lang.invoke.MethodHandleNatives.resolve(Native Method)
at java.lang.invoke.MemberName $ Factory.resolve(MemberName)的.java:975) java.lang.invoke.MemberName $ $ $ b $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $
我不明白这个错误的来源。方法void setId(Long)确实存在。
public String computeSetterName (String fieldName){
returnset+ fieldName.substring(0,1).toUpperCase()+ fieldName.substring(1);
}
电话:
ISetter setter = accessorFactory.getSetter(TestEntity.class,id,Long.class);
解决方案您的代码中存在一些错误。
首先,你使用 Void.class
,你应该使用 void.class
代替。
其次, func.generic
返回(对象,对象) )对象
,你真正想要的是 func.erase
,所以保留了返回类型((Object,Object) void
)。
第三,建议不要使用原始类型,我建议改为以下实现:
public static< T,R> ISetter< T,R> getSetter(Class< T> clazz,String fieldName,
Class< R> fieldType)抛出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( ),
目标,
func
);
MethodHandle factory = site.getTarget();
ISetter< T,R> r =(ISetter< T,R>)factory.invoke();
返回r;
}
这对我有用: http://ideone.com/KKx10r
I'm trying to get a lambda method handle for the setter of a private field, but for some reason, the setter cannot be found.
This is the functional interface I am using:
@FunctionalInterface
public interface ISetter<T, R> {
void set(T object, R value);
}
And this the method used to fetch the setter:
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;
}
All setters are, by convention, named the same: "setField(...)".
This is my test class:
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;
}
}
But when I execute this method for "id" and "Long.class" I get the follow 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
I don't understand where this error is coming from. The method "void setId(Long)" does exist.
public String computeSetterName(String fieldName) {
return "set" + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);
}
And the call:
ISetter setter = accessorFactory.getSetter(TestEntity.class, "id", Long.class);
解决方案 There are a few mistakes in your code.
First, you are using Void.class
, you should use void.class
instead.
Second, func.generic
returns (Object,Object)Object
, what you really want is func.erase
, so the return type is retained ((Object,Object)void
).
Third, it advisable not to use raw types, I would propose the following implementation instead:
public static <T, R> ISetter<T, R> getSetter(Class<T> clazz, String fieldName,
Class<R> 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<T, R> r = (ISetter<T, R>) factory.invoke();
return r;
}
Which works for me: http://ideone.com/KKx10r
这篇关于Java8从类中检索lambda setter的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!