一、使用反射调用方法
public class User {
public int id;
private String name;
String address;
protected int sno;
public User() {
}
public User(int id, String name, String address, int sno) {
super();
this.id = id;
this.name = name;
this.address = address;
this.sno = sno;
}
public void study() {
System.out.println("study...");
}
public void eat(int a,String b) {
System.out.println("eat...");
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", address=" + address + ", sno=" + sno + "]";
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((address == null) ? 0 : address.hashCode());
result = prime * result + id;
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + sno;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
User other = (User) obj;
if (address == null) {
if (other.address != null)
return false;
} else if (!address.equals(other.address))
return false;
if (id != other.id)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (sno != other.sno)
return false;
return true;
}
}
import java.lang.reflect.Method;
public class Test {
public static void main(String[] args) throws Exception {
Class usrClass = Class.forName("com.lzj.reflect.pojo.User");
Object obj = usrClass.newInstance();
Method eatMethod = usrClass.getDeclaredMethod("eat", int.class, String.class);
Object retValue = eatMethod.invoke(obj, 3,"lzj");
System.out.println(retValue);
}
}
二、invoke()
@CallerSensitive
public Object invoke(Object obj, Object... args)
throws IllegalAccessException, IllegalArgumentException,
InvocationTargetException
{
if (!override) {
if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) {
Class<?> caller = Reflection.getCallerClass();
checkAccess(caller, clazz, obj, modifiers);
}
}
MethodAccessor ma = methodAccessor;
if (ma == null) {
ma = acquireMethodAccessor();
}
return ma.invoke(obj, args);
}
- 第一个参数是方法属于的对象(如果是静态方法,则可以直接传 null)
- 第二个可变参数是该方法的参数
- Method.invoke()本身要用数组包装参数;而且每次调用都必须检查方法的可见性(在Method.invoke()里),也必须检查每个实际参数与形式参数的类型匹配性(在NativeMethodAccessorImpl.invoke0()里或者生成的Java版MethodAccessor.invoke()里)
1. 实现原理
- invoke()实际上并不是自己实现的反射调用逻辑,而是委托给sun.reflect.MethodAccessor来处理,每个实际的Java方法只有一个对应的Method对象作为root,这个root是不会暴露给用户的,而是每次在通过反射获取Method对象时,新创建Method对象把root包装起来再给用户,在第一次调用一个实际Java方法对应的Method对象的invoke()方法之前,实现调用逻辑的MethodAccessor对象还没创建,等第一次调用时才新创建MethodAccessor并更新给root,然后调用MethodAccessor.invoke()真正完成反射调用