Java 反射，开发框架必备技能
Java 反射，开发框架必备技能
netkiller old
发布于 2018-03-05 17:49:06
发布于 2018-03-05 17:49:06
反射一般开发者接触不到，反射主要用户框架的开发。例如我举一个例子你就明白了：
http://www.netkiller.cn/news/list/2.html
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，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);本文节选自《Netkiller Java 手札》
1.9. Reflection 反射
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
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。
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());
}
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); static 方法调用时，不必得实例化对象
Class cls = Class.forName("cn.netkiller.reflect.Student");
Method staticMethod = cls.getDeclaredMethod("setAge",int.class);
staticMethod.invoke(cls,20); //这里不需要newInstance 本文参与 腾讯云自媒体分享计划，分享自微信公众号。
原始发表：2016-10-20，如有侵权请联系 cloudcommunity@tencent.com 删除
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