java reflection

Person

package com.yuankai;
public class Person {
	
	
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		return getName()+getAge();
	}

	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;
	}

	private String name;
	private int age;
	
	//加載class文件時執行
//	static {
//		System.out.println("class load");
//	}
//	
	public Person(String name, int age) {
//		System.out.println("construct 2");
		this.age = age;
		this.name = name;
	}
	public Person() {
//		System.out.println("construct method");
	}
	
	//實例化對象時執行，比構造方法早執行
//	{
//		System.out.println("blank ");
//	}
}

測試例子

package com.yuankai;

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


public class ReflectDemo {

	public static void main(String[] args) throws Exception {
		
//		demo1();
//		demo2();
//		demo3();
//		demo4();
//		demo5();
//		demo6();
		
	}
	
	public static void demo1() {
		Person p = new Person();
		if(p.getClass().getPackage() == null) {
			System.out.println("package is null");
		} else {
			
			System.out.println(p.getClass().getPackage().getName());
		}
		System.out.println(p.getClass().getName());
		
	}
	
	public static void demo2() throws ClassNotFoundException {
		Class class1 = null;
		Class<?> class2 = null;
		
		//Class.forName 類加載器會把對應的Class文件加載進來
		class1 = Class.forName("com.yuankai.Person");
		//Person.class 類加載器不會把Person對應的Class加載進來
		class2 = Person.class;
	}
	
	public static void demo3() throws InstantiationException, IllegalAccessException, ClassNotFoundException {
		Person p = (Person) Class.forName("com.yuankai.Person").newInstance();
		p.setAge(10);
		p.setName("test");
		System.out.println(p.toString());
	}
	
	public static void demo4() throws InstantiationException, IllegalAccessException, ClassNotFoundException, IllegalArgumentException, InvocationTargetException {
		Class<?> class1 = null;
		class1 = Class.forName("com.yuankai.Person");
		
		//注意class的構造方法的順序
		//構造方法定義的順序與cons的下標值一致
		Constructor<?>[] cons = class1.getConstructors();
		for(int i=0; i<cons.length; i++) {
			System.out.println(cons[i].toString());
		}
		Person p = (Person) cons[0].newInstance("yuankai", 32);
		Person p1 = (Person) cons[1].newInstance();
		System.out.println(p.toString());
		System.out.println(p1.toString());
	}
	
	public static void demo5() throws Exception {
		Class<?> class1 =  Class.forName("com.yuankai.Person");
		//newInstance只會調用無參數的構造方法
		Object obj = class1.newInstance();
		
		Field f = class1.getDeclaredField("name");
		f.setAccessible(true);
		f.set(obj, "this name");
		System.out.println("alter the feature :" + f.get(obj));
	}
	
	public static void demo6() throws Exception {
		//AppClassLoader 加載classpath指定的類，是最常用的加載器。同時也是java中默認的加載器
		String classLoaderName = Person.class.getClassLoader().getClass().getName();
		System.out.println(classLoaderName);
	}
	
	public static void demo7() throws Exception {
		//這個是測試Class文件什麼情況下加載的
		Class<?> c = Person.class;
		System.out.println("======");
		Class.forName("com.yuankai.Person");
	}

}

反射機制應用於工廠模式：

package Reflect;
 
import java.io.*;
import java.util.*;
 
interface fruit{
    public abstract void eat();
}
 
class Apple implements fruit{
    public void eat(){
        System.out.println("Apple");
    }
}
 
class Orange implements fruit{
    public void eat(){
        System.out.println("Orange");
    }
}
 
//操作屬性文件類
class init{
    public static Properties getPro() throws FileNotFoundException, IOException{
        Properties pro=new Properties();
        File f=new File("fruit.properties");
        if(f.exists()){
            pro.load(new FileInputStream(f));
        }else{
            pro.setProperty("apple", "Reflect.Apple");
            pro.setProperty("orange", "Reflect.Orange");
            pro.store(new FileOutputStream(f), "FRUIT CLASS");
        }
        return pro;
    }
}
 
class Factory{
    public static fruit getInstance(String ClassName){
        fruit f=null;
        try{
            f=(fruit)Class.forName(ClassName).newInstance();
        }catch (Exception e) {
            e.printStackTrace();
        }
        return f;
    }
}
class hello{
    public static void main(String[] a) throws FileNotFoundException, IOException{
        Properties pro=init.getPro();
        fruit f=Factory.getInstance(pro.getProperty("apple"));
        if(f!=null){
            f.eat();
        }
    }
}

反射 模擬hibernate中Session的save方法

package com.yuankai;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.util.HashMap;
import java.util.Map;

public class Session {
	
	private String tableName = "_Person";
	private Map<String, String> sfs = new HashMap<>();
	private String []methodName = null;
	
	public Session() {
		sfs.put("_id", "id");
		sfs.put("_name", "name");
		sfs.put("_age", "age");
		methodName = new String[sfs.size()];
	}
	
	public void save(Person p) throws Exception {
		String sql = createSql();
		//數據庫相關操作
		for(String name : methodName) {
			Method m = Person.class.getMethod(name);
			Class r = m.getReturnType();
			System.out.println(m.getName()+"!" + r.getName());
			if(r.getName().equals("java.lang.String")) {
				String returnValue = (String) m.invoke(p);
			}
		}
	}
	
	public String createSql() throws Exception {
		Session s = new Session();
		StringBuilder str2 = new StringBuilder();
		int index = 0;
		for(int i=0; i<sfs.size(); i++) {
			str2.append("?,");
		}
		
		String str1 = "";
		for(String s1 : sfs.keySet()) {
			String v = sfs.get(s1);
			v = Character.toUpperCase(v.charAt(0)) + v.substring(1);
			methodName[index] = "get"+v;
			index++;
			str1 += s1+",";
		}
		str1 = str1.substring(0, str1.length()-1);
		//這個要注意index值得問題，下標應該從0開始
		str2.deleteCharAt(str2.length()-1);
		
		System.out.println(str2.toString());
		System.out.println(str1);
		String sql = "insert into " + tableName +"(" +str1 +") values(" + str2 +")";
		System.out.println(sql);
		
		for(int i=0; i<methodName.length; i++) {
			System.out.println(methodName[i]);
		}
		return sql;
	}
	
	
}