[英]Set private field value with reflection
I have 2 classes: Father
and Child
我有 2 个班级: Father
和Child
public class Father implements Serializable, JSONInterface {
private String a_field;
//setter and getter here
}
public class Child extends Father {
//empty class
}
With reflection I want to set a_field
in Child
class:通过反射,我想在Child
类中设置a_field
:
Class<?> clazz = Class.forName("Child");
Object cc = clazz.newInstance();
Field f1 = cc.getClass().getField("a_field");
f1.set(cc, "reflecting on life");
String str1 = (String) f1.get(cc.getClass());
System.out.println("field: " + str1);
but I have an exception:但我有一个例外:
Exception in thread "main" java.lang.NoSuchFieldException: a_field线程“main”中的异常 java.lang.NoSuchFieldException: a_field
But if I try:但如果我尝试:
Child child = new Child();
child.setA_field("123");
it works.有用。
Using setter method I have same problem:使用 setter 方法我有同样的问题:
method = cc.getClass().getMethod("setA_field");
method.invoke(cc, new Object[] { "aaaaaaaaaaaaaa" });
To access a private field you need to set Field::setAccessible
to true.要访问私有字段,您需要将Field::setAccessible
设置为 true。 You can pull the field off the super class.你可以把这个领域从超类中拉出来。 This code works:此代码有效:
Class<?> clazz = Child.class;
Object cc = clazz.newInstance();
Field f1 = cc.getClass().getSuperclass().getDeclaredField("a_field");
f1.setAccessible(true);
f1.set(cc, "reflecting on life");
String str1 = (String) f1.get(cc);
System.out.println("field: " + str1);
Using FieldUtils
from the Apache Commons Lang 3 :使用Apache Commons Lang 3 中的FieldUtils
:
FieldUtils.writeField(childInstance, "a_field", "Hello", true);
The true
forces it to set, even if the field is private .即使该字段是private , true
也会强制设置它。
This one can access private fields as well without having to do anything这个也可以访问私有字段而无需做任何事情
import org.apache.commons.lang3.reflect.FieldUtils;
Object value = FieldUtils.readField(entity, fieldName, true);
Kotlin verison Kotlin 版本
Get private variable using below extension functions使用以下扩展函数获取私有变量
fun <T : Any> T.getPrivateProperty(variableName: String): Any? {
return javaClass.getDeclaredField(variableName).let { field ->
field.isAccessible = true
return@let field.get(this)
}
}
Set private variable value get the variable设置私有变量值获取变量
fun <T : Any> T.setAndReturnPrivateProperty(variableName: String, data: Any): Any? {
return javaClass.getDeclaredField(variableName).let { field ->
field.isAccessible = true
field.set(this, data)
return@let field.get(this)
}
}
Get variable use:获取变量使用:
val bool = <your_class_object>.getPrivateProperty("your_variable") as String
Set and get variable use:设置和获取变量使用:
val bool = <your_class_object>.setAndReturnPrivateProperty("your_variable", true) as Boolean
val str = <your_class_object>.setAndReturnPrivateProperty("your_variable", "Hello") as String
Java version爪哇版
public class RefUtil {
public static Field setFieldValue(Object object, String fieldName, Object valueTobeSet) throws NoSuchFieldException, IllegalAccessException {
Field field = getField(object.getClass(), fieldName);
field.setAccessible(true);
field.set(object, valueTobeSet);
return field;
}
public static Object getPrivateFieldValue(Object object, String fieldName) throws NoSuchFieldException, IllegalAccessException {
Field field = getField(object.getClass(), fieldName);
field.setAccessible(true);
return field.get(object);
}
private static Field getField(Class mClass, String fieldName) throws NoSuchFieldException {
try {
return mClass.getDeclaredField(fieldName);
} catch (NoSuchFieldException e) {
Class superClass = mClass.getSuperclass();
if (superClass == null) {
throw e;
} else {
return getField(superClass, fieldName);
}
}
}
}
Set private value use设置私有值使用
RefUtil.setFieldValue(<your_class_object>, "your_variableName", newValue);
Get private value use获取私有值使用
Object value = RefUtil.getPrivateFieldValue(<your_class_object>, "your_variableName");
You can use Manifold's @Jailbreak for direct, type-safe Java reflection:您可以使用Manifold 的@Jailbreak进行直接的、类型安全的 Java 反射:
@Jailbreak Child child = new Child();
child.a_field = "123;
@Jailbreak
unlocks the child local variable in the compiler for direct access to all the members in Child
's hierarchy. @Jailbreak
在编译器中解锁子局部变量,以便直接访问Child
层次结构中的所有成员。
Similarly you can use the jailbreak() extension method for one-off use:同样,您可以使用jailbreak()扩展方法进行一次性使用:
child.jailbreak().a_field = "123";
Through the jailbreak()
method you can access any member in Child
's hierarchy.通过jailbreak()
方法,您可以访问Child
层次结构中的任何成员。
In both cases the compiler resolves the field access for you type-safely, as if a public field, while Manifold generates efficient reflection code for you under the hood.在这两种情况下,编译器都会以类型安全的方式为您解析字段访问,就像公共字段一样,而 Manifold 会在幕后为您生成高效的反射代码。
As per the Javadoc of Class.getField
(emphasis mine):根据Class.getField
的 Javadoc(重点是我的):
Returns a Field object that reflects the specified public member field of the class or interface represented by this Class object.返回一个 Field 对象,该对象反映了此 Class 对象表示的类或接口的指定公共成员字段。
This method only returns public fields.此方法仅返回公共字段。 Since a_field
is private, it won't be found.由于a_field
是私有的,因此不会被找到。
Here's a working code:这是一个工作代码:
public class Main {
public static void main(String[] args) throws Exception {
Class<?> clazz = Class.forName("Child");
Object cc = clazz.newInstance();
Field f1 = cc.getClass().getField("a_field");
f1.set(cc, "reflecting on life");
String str1 = (String) f1.get(cc);
System.out.println("field: " + str1);
}
}
class Father implements Serializable {
public String a_field;
}
class Child extends Father {
//empty class
}
Note that I also changed your line String str1 = (String) f1.get(cc.getClass());
请注意,我还更改了您的行String str1 = (String) f1.get(cc.getClass());
to String str1 = (String) f1.get(cc);
to String str1 = (String) f1.get(cc);
because you need to give the object of the field, not the class.因为你需要给出字段的对象,而不是类。
If you want to keep your field private, then you need to retrieve the getter / setter method and invoke those instead.如果你想保持你的字段私有,那么你需要检索 getter / setter 方法并调用它们。 The code you have given does not work because, to get a method, you also need to specify it's arguments, so您提供的代码不起作用,因为要获取方法,您还需要指定它的参数,所以
cc.getClass().getMethod("setA_field");
must be必须是
cc.getClass().getMethod("setA_field", String.class);
Here's a working code:这是一个工作代码:
public class Main {
public static void main(String[] args) throws Exception {
Class<?> clazz = Class.forName("Child");
Object cc = clazz.newInstance();
cc.getClass().getMethod("setA_field", String.class).invoke(cc, "aaaaaaaaaaaaaa");
String str1 = (String) cc.getClass().getMethod("getA_field").invoke(cc);
System.out.println("field: " + str1);
}
}
class Father implements Serializable {
private String a_field;
public String getA_field() {
return a_field;
}
public void setA_field(String a_field) {
this.a_field = a_field;
}
}
class Child extends Father {
//empty class
}
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