Java 反射，开发框架必备技能

通过反射技术我们将上面的统一资源定位付(URL) 映射到Class 相当于

class: news

method: list

parameter: 2

差不多就是下面样子

class News{

    public String list(String catagory_id){

        ...

        ...

    }

}

 

我们只需要在框架核心中分析 url 然后调用对应的方法下载，于此同时将参数传递过去。

 

Class<?> cls = Class.forName("cn.netkiller.reflect.News");
Object obj= cls.newInstance();
Method method = cls.getDeclaredMethod("list", int.class);
return method.invoke(obj, 2);

 

1.9. Reflection 反射下载

this.getClass().getName() //当前Class名字
Thread.currentThread().getStackTrace()[1].getMethodName()); //当前方法名

1.9.1. 获得所有变量

Field[] fields = objClass.getFields();
for (Field field : fields) {
System.out.println(field.getName());
}

注意：只能去除 public变量

1.9.2. 批量赋值

1.9.3. 方法操作

JAVA反射调用方法的步骤有三步

得到要调用类的class
得到要调用的类中的方法(Method)
方法调用(invoke)

1.9.3.1. 获得所有方法

下载

Class<?> objClass = a.getClass();
Method[] methods =  objClass.getDeclaredMethods();
for (Method method : methods) {
System.out.println(method);
}

1.9.3.2. set/get 方法

package cn.netkiller.reflect;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Member {
public String name;
private int age;

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

@Override
public String toString() {
return "ClassA [name=" + name + ", age=" + age + "]";
}

public Member() {
// TODO Auto-generated constructor stub
}

public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {
Class<?> cls = Class.forName("cn.netkiller.reflect.Member");
Object member = cls.newInstance();
Method setMethod = cls.getDeclaredMethod("setAge", int.class);
setMethod.invoke(member, 15);

Method getMethod = cls.getDeclaredMethod("getAge");
System.out.println(getMethod.invoke(member));

}

}

下面做一个稍微复杂点的例子，ClassB继承ClassA，取出ClassA的成员变量赋值到ClassA。

下载

package cn.netkiller.reflect;

public class ClassA {
public String name;
private int age;

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public ClassA() {
// TODO Auto-generated constructor stub
}

@Override
public String toString() {
return "ClassA [name=" + name + ", age=" + age + "]";
}
}

package cn.netkiller.reflect;

public class ClassB extends ClassA{

public ClassB() {
// TODO Auto-generated constructor stub
}
private String address;

public String getAddress() {
return address;
}

public void setAddress(String address) {
this.address = address;
}

@Override
public String toString() {
return "ClassB [address=" + address + "]";
}

}

package cn.netkiller.reflect;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class ReflectionTest {

public ReflectionTest() {
// TODO Auto-generated constructor stub
}

public void testSetMethod() throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, InstantiationException {

// ClassA a = new ClassA();

ClassB b = new ClassB();
b.setAddress("Shenzhen");

Class<ClassA> classA = ClassA.class;
ClassA a = classA.newInstance();
a.setName("Neo");
a.setAge(30);

System.out.println(classA.getDeclaredMethod("getAge").invoke(a));

Method m = classA.getDeclaredMethod("setAge", int.class);
m.setAccessible(true); // 因为写成private 所以这里必须设置
m.invoke(b, 26);

System.out.println(a.toString());
System.out.println(b.toString());

System.out.println(b.getName());
System.out.println(b.getAge());
}下载

public static void main(String[] args) throws InvocationTargetException {

ReflectionTest rt = new ReflectionTest();
try {
rt.testSetMethod();

} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

}

set 方法

System.out.println(classA.getDeclaredMethod("getAge").invoke(a));

get 方法

Method m = classA.getDeclaredMethod("setAge", int.class);
m.setAccessible(true);	//因为写成private 所以这里必须设置
m.invoke(b, 26);

1.9.3.3. static 方法调用

 

Class cls = Class.forName("cn.netkiller.reflect.Student");
Method setMethod = cls.getDeclaredMethod("setAge",int.class);
setMethod.invoke(cls.newInstance(), 15);