hibernate:一

Struts2 控制器线程安全问题

和所有Web应用一样, Struts2 也工作在多线程并发模式. Struts2 的控制器也有线程并发问题. 当Spring将Struts2 的控制器作为单例对象管理时将有线程并发错误发生:

一个有并发错误的案例:

编写控制器:

@Controllerpublic class TestAction {    private String name;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;        Thread t = Thread.currentThread();        System.out.println(t+" set "+name);    }    public String save() throws Exception{        Thread.sleep(5000);        Thread t = Thread.currentThread();        System.out.println(t+" save "+name);        return "success";    }}

配置组件扫描: spring-struts2.xml

<context:component-scan base-package="ssh.day03"/>配置控制器: struts.xml<!-- 测试 线程并发安全问题 --><action name="test" class="testAction"    method="save">    <result name="success">        /WEB-INF/jsp/ok.jsp    </result></action>   

测试: 使用两个浏览器并发访问服务器时候出现并发错误结果:

无状态Bean: 一个Java对象中除了只读的实例变量以为, 没有其他变量时候, 这个Java Bean就是无状态的Bean, 无状态的Bean在多线程并发访问时候是线程安全的. 常见的业务层Bean就是典型的无状态Bean
解决办法:

-Struts2中的控制器无法做到无状态;
所有Struts2默认情况下为每个请求(线程)都创建了一个控制器实例, 这样就避免的多用户线程访问同一份对象属性的安全问题, 解决了线程安全问题.
利用Spring作为控制器工厂管理控制器时候, 应该利用@Scope(“prototype”)为每次请求创建新的控制器对象来解决线程安全问题.
案例: 如上案例只需要更新控制器, 添加@Scope(“prototype”)就可以解决线程安全问题.

代码如下:

@Controller@Scope("prototype")public class TestAction {    private String name;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;        Thread t = Thread.currentThread();        System.out.println(t+" set "+name);    }    public String save() throws Exception{        Thread.sleep(5000);        Thread t = Thread.currentThread();        System.out.println(t+" save "+name);        return "success";    }}

Hibernate

Hibernate: 冬眠

数据持久化ORM框架, 对象关系映射: 按照面向对象的方式操作关系型数据库,不用写任何的SQL语句了!

使用步骤:

1.导入Hibernate包 数据库驱动 和 JUnit:

<dependency>    <groupId>org.hibernate</groupId>    <artifactId>hibernate-core</artifactId>    <version>4.2.21.Final</version></dependency><!-- 添加mysql驱动 (不要选5.1.6) --><dependency>    <groupId>mysql</groupId>    <artifactId>mysql-connector-java</artifactId>    <version>5.1.40</version></dependency><!-- 添加junit用于实现单元测试 --><dependency>    <groupId>junit</groupId>    <artifactId>junit</artifactId>    <version>4.12</version></dependency>

2.配置主配置文件 hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-configuration PUBLIC    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration>    <session-factory>        <!-- Database connection settings -->        <property name="connection.driver_class">            com.mysql.jdbc.Driver        </property>        <property name="connection.url">            jdbc:mysql://localhost:3306/ssh        </property>        <property name="connection.username">            root        </property>        <property name="connection.password">            root        </property>        <!-- JDBC connection pool (use the built-in) -->        <property name="connection.pool_size">5</property>        <!-- SQL dialect 方言 -->        <property name="dialect">            org.hibernate.dialect.MySQL5Dialect        </property>        <!-- Enable Hibernate's automatic session context management -->        <property name="current_session_context_class">            thread        </property>        <!-- Disable the second-level cache -->        <property name="cache.provider_class">            org.hibernate.cache.NoCacheProvider</property>        <!-- Echo all executed SQL to stdout -->        <property name="show_sql">true</property>        <property name="format_sql">true</property>        <!-- Drop and re-create the database schema on startup -->        <!-- <property name="hbm2ddl.auto">update</property>-->        <mapping resource="mapping/User.hbm.xml" />    </session-factory></hibernate-configuration>

3.添加实体类:

public class User implements Serializable {    private static final long serialVersionUID = 6625365205378512919L;    private Integer id;    private String name;    private Integer age;    private Double salary;    private Date hiredate;    public User() {    }    public User(Integer id, String name, Integer age, Double salary, Date hiredate) {        super();        this.id = id;        this.name = name;        this.age = age;        this.salary = salary;        this.hiredate = hiredate;    }    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Integer getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }    public Double getSalary() {        return salary;    }    public void setSalary(Double salary) {        this.salary = salary;    }    public Date getHiredate() {        return hiredate;    }    public void setHiredate(Date hiredate) {        this.hiredate = hiredate;    }    @Override    public String toString() {        return "User [id=" + id + ", name=" + name + ", age=" + age + ", salary=" + salary + ", hiredate=" + hiredate                + "]";    }    @Override    public int hashCode() {        final int prime = 31;        int result = 1;        result = prime * result + ((id == null) ? 0 : id.hashCode());        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 (id == null) {            if (other.id != null)                return false;        } else if (!id.equals(other.id))            return false;        return true;    }}

4.创建数据库表:

create database ssh;use ssh;create table t_user(    t_id int,    t_name varchar(50),    t_age int,    t_salary double,    t_hiredate datetime,    primary key(t_id));

5.添加映射文件 mapping/User.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><!-- 映射文件: 将类映射到表, 将类中的属性映射到表的列 --><hibernate-mapping>    <class name="ssh.day03.User" table="t_user">        <!-- id 映射 主键 -->        <id name="id" column="t_id">            <generator class="increment"/>        </id>        <property name="name" column="t_name"/>        <property name="age" column="t_age"/>        <property name="salary" column="t_salary"/>        <property name="hiredate" column="t_hiredate"/>    </class></hibernate-mapping>

6.添加测试案例:

SessionFactory factory;@Beforepublic void init(){    Configuration cfg = new Configuration();    cfg.configure("hibernate.cfg.xml");    factory = cfg.buildSessionFactory();}@Afterpublic void destory(){    factory.close();}@Testpublic void testSave(){    User user=new User(            1, "Tom", 10, 4.5, new Date());    Session session = factory.openSession();    Transaction tx = session.beginTransaction();    session.save(user);    tx.commit();    session.close();}

测试…

7.测试Hibernate提供的CRUD功能

@Testpublic void testGet(){    Integer id=2;    Session session = factory.openSession();    User user=(User)session.get(User.class, id);    System.out.println(user);    session.close();}@Testpublic void testLoad(){    Integer id=1;    Session session = factory.openSession();    User user=(User)session.load(User.class, id);    System.out.println(user);    session.close();}@Testpublic void testUpdate(){    Session session = factory.openSession();    Transaction tx=session.beginTransaction();    User user = (User)session.get(User.class, 1);    user.setName("Nemo");    session.update(user);    tx.commit();    session.close();}@Testpublic void testDelete(){    Session session = factory.openSession();    Transaction tx=session.beginTransaction();    User user = (User)session.get(User.class, 1);    session.delete(user);    tx.commit();    session.close();}@Test public void testAdd(){    Session session = factory.openSession();    Transaction tx=session.beginTransaction();    User u1=new User(1, "Tom", 4, 4.5,new Date());    User u2=new User(2, "Jerry", 6, 9.5,new Date());    User u3=new User(3, "Andy", 8, 8.5,new Date());    session.save(u1);    session.save(u2);    session.save(u3);    tx.commit();    session.close();}@Testpublic void testFindAll(){    //sql: select * from t_user    //hql: from User    String hql="from User";    Session session = factory.openSession();    Query query = session.createQuery(hql);    List<User> list = query.list();    for (User user : list) {        System.out.println(user);    }    session.close();}@Testpublic void testFindAll2(){    //sql: select t_id, t_name from t_user    //hql: select new map(id as id, name as Name)    //     from User    Session session=factory.openSession();    String hql = "select new map(id as id, "            + "name as Name) from User";    Query query = session.createQuery(hql);    List<Map<String, Object>> list=query.list();    for (Map<String, Object> map : list) {        System.out.println(map);     }    session.close();}@Testpublic void testFindByParam(){    //sql: select * from t_user     //     where t_salary < ?    //hql: from User where salary<?    String hql="from User where salary<?";    Session session = factory.openSession();    Query query = session.createQuery(hql);    query.setDouble(0, 9);    List<User> list=query.list();    for (User user : list) {        System.out.println(user);     }    session.close();}@Testpublic void testFindNamedParam(){    String hql="from User where salary<:salary";    Session session=factory.openSession();    Query query=session.createQuery(hql);    //替换"名称"参数    query.setDouble("salary", 9);    List<User> list=query.list();    for (User user : list) {        System.out.println(user);     }    session.close();}

Hibernate 中对象生存周期管理

测试:

@Test
public void testAutoUpdate(){
//临时状态 user
User user = new User(
8, “Wang”, 4, 4.5, new Date());
Session session = factory.openSession();
Transaction tx = session.beginTransaction();
session.save(user);
//user 是持久状态了
user.setSalary(100.0);
session.flush();
tx.commit();
session.close();
}

@Test
public void testGetUser(){
Session session = factory.openSession();
Transaction tx = session.beginTransaction();
User u =(User)session.get(User.class, 8);
//u 是持久状态了
u.setName(“王”);
session.flush();
tx.commit();
session.close();
}

@Test
public void testState(){
Session session = factory.openSession();
Transaction tx=session.beginTransaction();
User user=(User)session.get(User.class, 8);
session.clear();
//session.evict(user);
//对象user为游离状态
user.setName(“Mac”);
//将user对象从游离状态切换为持久状态
session.update(user);
session.flush();
tx.commit();
session.close();
}

ID 生成问题

Hibernate 支持各种ID生成策略

第一种: 在最大值上加一

<!-- id 映射 主键 --><id name="id" column="t_id">    <generator class="increment"/></id>测试:@Testpublic void testId(){    User user = new User(        null, "范传奇", 5, 200.0, new Date());    Session session = factory.openSession();    Transaction tx=session.beginTransaction();    session.save(user);    //hibernate 会自动返回 生成的ID    System.out.println(user);    tx.commit();    session.close();}