JAVA反射与内省(Introspector)

什么是Java内省：内省是Java语言对Bean类属性、事件的一种缺省处理方法。

Java内省的作用：一般在开发框架时，当需要操作一个JavaBean时，如果一直用反射来操作，显得很麻烦；所以sun公司开发一套API专门来用来操作JavaBean.

反射就是运行时获取一个类的所有信息，可以获取到.class的任何定义的信息（包括成员 变量，成员方法，构造器等）

可以操纵类的字段、方法、构造器等部分。
内省基于反射实现，主要用于操作JavaBean，通过内省 可以获取bean的getter/setter

1. 内省

private static void tetsJavaIntrospector() throws Exception{
Class<?> cl = Class.forName("yiban.dao.Person");
// 在bean上进行内省
BeanInfo beaninfo = Introspector.getBeanInfo(cl, Object.class);
PropertyDescriptor[] pro = beaninfo.getPropertyDescriptors();
Person p = new Person();
System.out.print("Person的属性有:");
for (PropertyDescriptor pr : pro) {
System.out.print(pr.getName() + " ");
}
System.out.println("");
for (PropertyDescriptor pr : pro) {
// 获取beal的set方法
Method writeme = pr.getWriteMethod();
if (pr.getName().equals("name")) {
// 执行方法
writeme.invoke(p, "xiong");
}
if (pr.getName().equals("age")) {
writeme.invoke(p, "23");
}
// 获取beal的get方法
Method method = pr.getReadMethod();
System.out.print(method.invoke(p) + " ");

}
}
package yiban.dao;

Person:
public class Person {
private String name;
private String age;
public String amount;
public Person() {
super();
}

public Person(String name){
this(name,null);
}

public Person(String name, String age) {
super();
this.name = name;
this.age = age;
}

public String getName() {
return name;
}

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

public String getAge() {
return age;
}

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

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

public String getAmount() {
return amount;
}

public void setAmount(String amount) {
this.amount = amount;
}

@Override
protected Object clone() throws CloneNotSupportedException {
// TODO Auto-generated method stub
return super.clone();
}

}

2. 反射

反射详解参考: https://www.cnblogs.com/jalja/p/6084445.html
向原作者致敬,如有需要联系本人删除即可.

从上面引出一个例子:

java 使用BeanInfo实现bean实体与map之间的互相转换

java 使用BeanInfo实现bean实体与map之间的互相转换。 
public interface BeanInfo希望提供有关其 bean 的显式信息的 bean 实现者可以提供某个 BeanInfo 类，该类实现此 BeanInfo 接口并提供有关其 bean 的方法、属性、事件等显式信息

转载: http://blog.csdn.net/cuiyaoqiang/article/details/53582382

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

import com.bh.bean.User;

public class Test {

/**
* bean转map
*/
public Test() {
try {
Map<String, Object> user=beanTransformToMap(new User(1, "zs"));
Iterator<Entry<String, Object>> iterator = user.entrySet().iterator();
while(iterator.hasNext()){
Entry<String, Object> next = iterator.next();
System.out.println(next.getKey()+" "+next.getValue());
}

} catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException
| IntrospectionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**map转实体
* @param map
* @return
* @throws IllegalAccessException
* @throws IllegalArgumentException
* @throws InvocationTargetException
* @throws IntrospectionException
*/
private User mapTransformToBean(Map<String, Object> map) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, IntrospectionException{

User user=new User();
BeanInfo beanInfo = Introspector.getBeanInfo(user.getClass());
PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
for (PropertyDescriptor property : propertyDescriptors) {
String key = property.getName();
if (map.containsKey(key)) {
Object value = map.get(key);
//得到property对应的setter方法
Method setter = property.getWriteMethod();
setter.invoke(user, value);
}
}
return user;
}
/**实体转map
* @param user
* @return
* @throws IllegalAccessException
* @throws IllegalArgumentException
* @throws InvocationTargetException
* @throws IntrospectionException
*/
private Map<String, Object> beanTransformToMap(User user) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, IntrospectionException{

Map<String, Object> map = new HashMap<String, Object>();
BeanInfo beanInfo = Introspector.getBeanInfo(user.getClass());
PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
for (PropertyDescriptor property : propertyDescriptors) {
String key = property.getName();
// 过滤class属性
if (!key.equals("class")) {
// 得到property对应的getter方法
Method getter = property.getReadMethod();
Object value = getter.invoke(user);
map.put(key, value);
}
}
return map;
}
public static void main(String[] args) {

new Test();
}
}