如何使用方法句柄调用私有方法?
据我所知,只有两种可公开访问的Lookup
个实例:
MethodHandles.lookup()
MethodHandles.publicLookup()
并且都不允许不受限制的私人访问。
非公开Lookup.IMPL_LOOKUP
可以满足我的需求。是否有一些公共方法来获取它(假设SecurityManager允许它)?
答案 0 :(得分:9)
事实证明,使用Lookup#unreflect(方法)并暂时使方法可访问(除非在程序初始化期间完成,否则可能会引入小的安全问题)。
以下是Thorben回答的修改后的主要方法:
public static void main(String[] args) {
Lookup lookup = MethodHandles.lookup();
NestedTestClass ntc = new Program().new NestedTestClass();
try {
// Grab method using normal reflection and make it accessible
Method pm = NestedTestClass.class.getDeclaredMethod("gimmeTheAnswer");
pm.setAccessible(true);
// Now convert reflected method into method handle
MethodHandle pmh = lookup.unreflect(pm);
System.out.println("reflection:" + pm.invoke(ntc));
// We can now revoke access to original method
pm.setAccessible(false);
// And yet the method handle still works!
System.out.println("handle:" + pmh.invoke(ntc));
// While reflection is now denied again (throws exception)
System.out.println("reflection:" + pm.invoke(ntc));
} catch (Throwable e) {
e.printStackTrace();
}
}
答案 1 :(得分:3)
我不知道,如果这是你真正想要的。也许你可以提供一些关于你想用它实现什么的更多信息。
但是,如果您想访问Lookup.IMPL_LOOKUP
,可以像在此代码示例中那样进行操作:
public class Main {
public static void main(String[] args) {
Lookup myLookup = MethodHandles.lookup(); // the Lookup which should be trusted
NestedTestClass ntc = new Main().new NestedTestClass(); // test class instance
try {
Field impl_lookup = Lookup.class.getDeclaredField("IMPL_LOOKUP"); // get the required field via reflections
impl_lookup.setAccessible(true); // set it accessible
Lookup lutrusted = (Lookup) impl_lookup.get(myLookup); // get the value of IMPL_LOOKUP from the Lookup instance and save it in a new Lookup object
// test the trusted Lookup
MethodHandle pmh = lutrusted.findVirtual(NestedTestClass.class, "gimmeTheAnswer", MethodType.methodType(int.class));
System.out.println(pmh.invoke(ntc));
} catch (Throwable e) {
e.printStackTrace();
}
}
// nested class with private method for testing
class NestedTestClass{
@SuppressWarnings("unused")
private int gimmeTheAnswer(){
return 42;
}
}
}
它适用于JDK 7,但可以在JDK 8中打破。并且要小心!当我执行它时,我的防病毒软件发出了警报。 我认为没有公开或干净的方法来做到这一点。
我有类似的问题,最后找到了解决方案:Access non-public (java-native) classes from JDK (7)。
答案 2 :(得分:-2)
这是一个类似的解决方案,其中包含私人参数 函数(我碰巧有一个代码位于前一个项目中):
班级名称: InspectionTree.java
功能签名: private String getSamePackagePathAndName(String className,String classPath)
String firstName = "John";
String lastName = "Smith";
//call the class's constructor to set up the instance, before calling the private function
InspectionTree inspectionTree = new InspectionTree(firstName, lastName);
String privateMethodName ="getSamePackagePathAndName";
Class[] privateMethodArgClasses = new Class[] { String.class, String.class };
Method method =
inspectionTree.getClass().getDeclaredMethod(privateMethodName, privateArgClasses);
method.setAccessible(true);
String className = "Person";
String classPath = "C:\\workspace";
Object[] params = new Object[]{className, classPath};
//note the return type of function 'getSamePackagePathAndName' is a String, so we cast
//the return type here as a string
String answer= (String)method.invoke(inspectionTree, params);
method.setAccessible(false);