笔记：setAccessible方法启用/禁用访问控制权限

class A {

    private int i;

    public int getI() {

        return i;

    }

    private void setI(int i) {

        this.i = i;

    }

}

 Class<?> clazz = Class.forName("hadoopclient.A");

        

        Field iField = clazz.getDeclaredField("i");

        System.out.println("i: "+iField);

        Method getI = clazz.getMethod("getI", new Class[]{});

        System.out.println("getI:\t"+getI);

        Method setI = clazz.getDeclaredMethod("setI", new Class[]{int.class});

        System.out.println("setI:\t"+setI);

        

        Object newInstance = clazz.newInstance();

        

        Object returnValue = getI.invoke(newInstance,new Class<?>[]{});

        System.out.println("init:\t"+returnValue);

        

        setI.setAccessible(true); //若无此句将抛异常

        setI.invoke(newInstance, new Object[]{100});

        returnValue = getI.invoke(newInstance, new Class<?>[]{});

        System.out.println("invoke setI(100):\t"+returnValue);

         

    }

}

注意：

setAccessible(true) 并不是将方法的访问权限改成了public，而是取消java的权限控制检查。所以即使是public方法，其accessible 属相默认也是false

JDK 文档：

setAccessible

public void setAccessible(boolean flag) throws SecurityException

Set the accessible flag for this object to the indicated boolean value. A value of true indicates that the reflected object should suppress Java language access checking when it is used. A value of false indicates that the reflected object should enforce Java language access checks.

First, if there is a security manager, its checkPermission method is called with a ReflectPermission("suppressAccessChecks") permission.

A SecurityException is raised if flag is true but accessibility of this object may not be changed (for example, if this element object is a Constructor object for the class Class).

A SecurityException is raised if this object is a Constructor object for the class java.lang.Class, and flag is true.

Parameters:

flag - the new value for the accessible flag

Throws:

SecurityException - if the request is denied.

See Also:

SecurityManager.checkPermission(java.security.Permission), RuntimePermission