Java代理和映射是兩個(gè)在軟件開(kāi)發(fā)過(guò)程中非常常見(jiàn)的概念。代理指的是通過(guò)代理對(duì)象來(lái)訪問(wèn)原對(duì)象的方法，而不直接訪問(wèn)原對(duì)象。

代理模式在Java中已經(jīng)被廣泛應(yīng)用，它可以隱藏底層實(shí)現(xiàn)的細(xì)節(jié)，并可以對(duì)原對(duì)象進(jìn)行額外的控制。一個(gè)常見(jiàn)的例子就是使用代理對(duì)象來(lái)進(jìn)行網(wǎng)絡(luò)訪問(wèn)，這樣就可以在底層實(shí)現(xiàn)中添加一些安全措施。

public interface Subject {
void request();
}
public class RealSubject implements Subject {
public void request() {
System.out.println("真正的請(qǐng)求");
}
}
public class Proxy implements Subject {
private RealSubject realSubject;
public Proxy() {
this.realSubject = new RealSubject();
}
public void request() {
preRequest();
realSubject.request();
postRequest();
}
public void preRequest() {
System.out.println("在請(qǐng)求之前做一些操作");
}
public void postRequest() {
System.out.println("在請(qǐng)求之后做一些操作");
}
}

映射指的是將一個(gè)實(shí)體映射到另一個(gè)實(shí)體。在Java中，映射通常用于將對(duì)象和數(shù)據(jù)庫(kù)中的表進(jìn)行映射。

Java中經(jīng)典的映射框架是Hibernate，它可以將Java對(duì)象映射成數(shù)據(jù)庫(kù)中的表。Hibernate的映射功能非常強(qiáng)大，可以自動(dòng)地處理基于Java對(duì)象的持久性操作。

public class Person {
private int id;
private String name;
private int age;
// 省略Getter和Setter
}
public class PersonDao {
private SessionFactory sessionFactory;
public PersonDao() {
sessionFactory = new Configuration().configure().buildSessionFactory();
}
public void add(Person person) {
Session session = sessionFactory.openSession();
session.beginTransaction();
session.save(person);
session.getTransaction().commit();
session.close();
}
public void delete(int id) {
Session session = sessionFactory.openSession();
session.beginTransaction();
Person person = (Person) session.get(Person.class, id);
session.delete(person);
session.getTransaction().commit();
session.close();
}
public Person get(int id) {
Session session = sessionFactory.openSession();
session.beginTransaction();
Person person = (Person) session.get(Person.class, id);
session.getTransaction().commit();
session.close();
return person;
}
public ListgetAll() {
Session session = sessionFactory.openSession();
session.beginTransaction();
Listpersons = session.createQuery("from Person").list();
session.getTransaction().commit();
session.close();
return persons;
}
}