在持久層DAO層中，對資料庫操作有影響的增、刪、改都需要開啟事物，並在執行完增刪改之後要提交事物。但如果每個方法都這樣寫的話，那麼程式碼變顯得冗餘，採用動態代理的方式來實現這種需求的話，可以使程式碼更清晰簡潔，並且將事物和資料操作解耦。下面是簡單的模擬一下此案例，沒有真正的資料庫連線和事物，只是簡單的模擬。

1.Person.java

package cn.it.spring.proxy.dao;

public class Person {

	private Integer pid;
	private String pnameString;
//省略set和get方法，還有建構函式
}

2 . Transaction.java

package cn.it.spring.proxy.dao;
/**
 * 模擬事物類
 * @author Administrator
 *
 */
public class Transaction {
	/**
	 * 開啟事物
	 */
	public void beginTransaction(){
		System.out.println("beginTransaction");
	}
	/**
	 * 提交事物
	 */
	public void commit(){
		System.out.println("commit");
	}
}
 

3. PersonDao.java

package cn.it.spring.proxy.dao;

import java.util.List;

public interface PersonDao {
	public void savePerson();
	public void deletePerson();
	public void updatePerson();
	public List<Person> getPersons();
}

4. PersonDaoImpl.java

package cn.it.spring.proxy.dao;

import java.util.ArrayList;
import java.util.List;

public class PersonDaoImpl implements PersonDao {

	@Override
	public void savePerson() {
		System.out.println("savePerson");
	}

	@Override
	public void deletePerson() {
		System.out.println("deletePerson");
	}

	@Override
	public void updatePerson() {
		System.out.println("updatePerson");

	}

	@Override
	public List<Person> getPersons() {
		List<Person> persons = new ArrayList<>();
		Person person1 = new Person(1, "person1");
		Person person2 = new Person(2, "person2");
		persons.add(person1);
		persons.add(person2);
		return persons;
	}

}
 

5.MyInterceptor.java

package cn.it.spring.proxy.dao;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyInterceptor implements InvocationHandler {
	
	private Object target;
	private Transaction transaction;
	
	public MyInterceptor(Object target, Transaction transaction) {
		super();
		this.target = target;
		this.transaction = transaction;
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		
		if (method.getName().equals("savePerson")
				|| method.getName().equals("deletePerson")
				|| method.getName().equals("updatePerson")) {
                        //開啟事物
                        transaction.beginTransaction();
			method.invoke(target, args);//執行目標物件的目標方法
			//提交事物
                        transaction.commit();
			return null;
		}else {
			return method.invoke(target, args);
		}
		
		
	}

}
 

6. 測試類PersonDaoTest.java

package cn.it.spring.proxy.dao;

import java.lang.reflect.Proxy;

import org.junit.Test;

public class PersonDaoTest {

	@Test
	public void test(){
		Transaction transaction = new Transaction();
		PersonDao target = new PersonDaoImpl();
		MyInterceptor interceptor = new MyInterceptor(target, transaction);
		PersonDao personDao = (PersonDao) Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), interceptor);
		personDao.deletePerson();
		System.out.println("=============================");
		personDao.savePerson();
		System.out.println("=============================");
		personDao.updatePerson();
		System.out.println("=============================");
		for(Person person : personDao.getPersons()){
			System.out.println(person.getPnameString());
		}
	}
}

7.結果