软件开发项目实践（二）

1. 利用MyBatis结合Junit、Log4j实现对数据库的增删改查。
导入MyBatis、Junit、Log4j和mysql驱动包，IntelliJ导包操作：File -> Project Structure -> Modules(左侧栏) -> 找到”+”，选择JARs -> 选择对应包路径即可。

确定各个包做的事情：

1. MyBatis：主要解决了之前使用JDBC对数据库进行操作的繁杂步骤，是一种ORM。
2. Junit：java测试框架。
3. Log4j：主要用户log记录。
4. mysql驱动：为java连接mysql数据库提供驱动及操作承载。

实验步骤：

1. 安装mysql数据库，创建数据库，创建表。为方便进行实验，我创建的user表结构如下：

   +------------+-------------+------+-----+-------------------+-----------------------------+
   | Field      | Type        | Null | Key | Default           | Extra                       |
   +------------+-------------+------+-----+-------------------+-----------------------------+
   | id         | int(11)     | NO   | PRI | NULL              | auto_increment              |
   | passwd     | varchar(16) | NO   |     | NULL              |                             |
   | nickname   | varchar(20) | NO   |     | NULL              |                             |
   | createTime | timestamp   | NO   |     | CURRENT_TIMESTAMP |                             |
   | updateTime | datetime    | YES  |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
   +------------+-------------+------+-----+-------------------+-----------------------------+

2. 创建java工程。导包。

3. 编写User实例。

   public class User {
   
       private Integer id;
       private String passwd;
       private String nickname;
   
       public Integer getId() {
           return id;
       }
   
       public void setId(Integer id) {
           this.id = id;
       }
   
       public String getPasswd() {
           return passwd;
       }
   
       public void setPasswd(String passwd) {
           this.passwd = passwd;
       }
   
       public String getNickname() {
           return nickname;
       }
   
       public void setNickname(String nickname) {
           this.nickname = nickname;
       }
   }

4. 编写User.xml mapper文件。该文件可以暂时认为是之前JDBC做的事情，在此配置好User实例中对应的方法要操作数据库的事情。

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE mapper
           PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
           "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   
   <!-- mapper标签要指定namespace属性，不然会报错，可看做包名-->
   <mapper namespace="com.pjhubs.dao.intf.UserDAO">
       <select id="selectUserWithID" parameterType="int" resultType="com.pjhubs.instance.User">
           select * from user where id = #{id}
       </select>
       <select id="selectAllUser" resultType="com.pjhubs.instance.User">
           select * from user
       </select>
       <insert id="insertUser" parameterType="com.pjhubs.instance.User">
           insert into user(nickname,passwd) values(#{nickname},#{passwd})
       </insert>
       <delete id="deleteUserWithID" parameterType="int">
           delete from user where id=#{id}
       </delete>
       <update id="updateUserWithNickname" parameterType="com.pjhubs.instance.User">
           update user set nickname=#{nickname} where id=#{id}
       </update>
   </mapper>

5. 编写MyBatis配置文件，SqlMapConfig.xml

   <?xml version="1.0" encoding="UTF-8" ?>
   <!DOCTYPE configuration
           PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
           "http://mybatis.org/dtd/mybatis-3-config.dtd">
   <configuration>
       <environments default="development">
           <environment id="development">
               <transactionManager type="JDBC"/>
               <dataSource type="POOLED">
                   <property name="driver" value="com.mysql.jdbc.Driver"/>
                   <property name="url" value="jdbc:mysql://localhost:3306/your_database_name?useSSL=false"/>
                   <property name="username" value="your_database_name"/>
                   <property name="password" value="your_database_password"/>
               </dataSource>
           </environment>
       </environments>
       <mappers>
           <mapper resource="User.xml"/>
       </mappers>
   </configuration>

6. 编写User接口及其实现。

   // ---------- user interface ---------
   import java.util.List;
   import com.pjhubs.instance.User;
   
   public interface UserDAO {
   
       public User selectUserWithID(int ID) throws Exception;
       public List<User> selectAllUser() throws Exception;
       public void insertUser(User user) throws Exception;
       public void deleteUserWithID(int ID) throws Exception;
       public void updateUserWithNickname(User user) throws Exception;
   
   }
   
   // ---------- user implements -----------
   import java.io.InputStream;
   import java.util.ArrayList;
   import java.util.List;
   
   import org.apache.ibatis.io.Resources;
   import org.apache.ibatis.session.SqlSession;
   import org.apache.ibatis.session.SqlSessionFactory;
   import org.apache.ibatis.session.SqlSessionFactoryBuilder;
   
   import com.pjhubs.dao.intf.UserDAO;
   import com.pjhubs.instance.User;
   
   public class UserDAOImpl implements UserDAO {
   
       @Override
       public User selectUserWithID(int ID) throws  Exception {
           String resource = "SqlMapConfig.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
           SqlSession session = factory.openSession();
           User user = session.selectOne("user.selectUserWithID", ID);
           session.close();
           return user;
       }
   
       @Override
       public List<User> selectAllUser() {
           List<User> usersList = new ArrayList<User>();
           try {
               String resource = "SqlMapConfig.xml";
               InputStream inputStream = Resources.getResourceAsStream(resource);
               SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
               SqlSession session = factory.openSession();
               usersList = session.selectList("user.selectAllUser");
               session.close();
           } catch (Exception e) {
               System.out.println(e);
           }
           return usersList;
       }
   
       @Override
       public void insertUser(User user) throws Exception {
           String resource = "SqlMapConfig.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
           SqlSession session = factory.openSession();
           session.insert("user.insertUser", user);
           // insert、Update、delete 加上 commit
           session.commit();  
           session.close();
       }
   
       @Override
       public void deleteUserWithID(int ID) throws Exception {
           String resource = "SqlMapConfig.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
           SqlSession session = factory.openSession();
           session.delete("user.deleteUserWithID", ID);
           // insert、Update、delete 加上 commit
           session.commit();   
           session.close();
       }
   
       @Override
       public void updateUserWithNickname(User user) throws Exception {
           String resource = "SqlMapConfig.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
           SqlSession session = factory.openSession();
           session.update("user.updateUserWithNickname", user);
           // insert、Update、delete 加上 commit
           session.commit();   
           session.close();
       }
   }

7. 使用Junit进行测试。

   import java.util.List;
   import org.junit.jupiter.api.Test;
   
   import com.pjhubs.instance.User;
   import com.pjhubs.dao.intf.UserDAO;
   import com.pjhubs.dao.impl.UserDAOImpl;
   
   public class UserTest {
   
       @Test
       public void testSelectAllUser() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           List<User> userList = userDAO.selectAllUser();
           for (User user : userList) {
               System.out.println("id：" + user.getId() + "昵称：" + user.getNickname());
           }
       }
   
       @Test
       public void testSelectUserWithID() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           User user = userDAO.selectUserWithID(1);
           System.out.println("id:" + user.getId() + " 昵称:" + user.getNickname());
       }
   
       @Test
       public void testInsertUser() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           User user = new User();
           user.setNickname("PJHubs");
           user.setPasswd("woaiwoziji123");
           userDAO.insertUser(user);
       }
   
       @Test
       public void testDeleteUserByID() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           userDAO.deleteUserWithID(1);
       }
   
       @Test
       public void testUpdateUserNickname() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           User user = new User();
           user.setNickname("pjhubs");
           user.setId(1);
           user.setPasswd("woaiwoziji123");
           userDAO.updateUserWithNickname(user);
       }
   
   }

8. 使用Junit编写测试类，

   import java.util.List;
   import org.junit.jupiter.api.Test;
   
   import com.pjhubs.instance.User;
   import com.pjhubs.dao.intf.UserDAO;
   import com.pjhubs.dao.impl.UserDAOImpl;
   
   public class UserTest {
   
       @Test
       public void testSelectAllUser() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           List<User> userList = userDAO.selectAllUser();
           for (User user : userList) {
               System.out.println("id：" + user.getId() + "昵称：" + user.getNickname());
           }
       }
   
       @Test
       public void testSelectUserWithID() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           User user = userDAO.selectUserWithID(1);
           System.out.println("id:" + user.getId() + " 昵称:" + user.getNickname());
       }
   
       @Test
       public void testInsertUser() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           User user = new User();
           user.setNickname("PJHubs");
           user.setPasswd("woaiwoziji123");
           userDAO.insertUser(user);
       }
   
       @Test
       public void testDeleteUserByID() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           userDAO.deleteUserWithID(1);
       }
   
       @Test
       public void testUpdateUserNickname() throws Exception {
           UserDAO userDAO = new UserDAOImpl();
           User user = new User();
           user.setNickname("pjhubs");
           user.setId(1);
           user.setPasswd("woaiwoziji123");
           userDAO.updateUserWithNickname(user);
       }
   
   }

至此经过八个步骤，实验完成，但还有个可以优化的地方，会发现其实在给UserDAO写implements时出现了非常多的重复性代码，经过一番搜索，发现可以使用MyBatis提供的Mapper代理开发模式进行优化，这个模式的意思是说，coder只需要编写mapper接口，可以认为是之前写的UserDAO interface，而不用再写具有相当多的重复性代码的implements，因为MyBatis会自动为Mapper接口生成动态代理实现类，编写Mapper接口类需要注意一下事项：

1. mapper接口的全限定名（包名）要和mapper映射文件的namespace的值相同。
2. mapper接口的方法名称要和mapper映射文件中的statement的id相同。
3. mapper接口的方法参数只能有一个，且类型要和mapper映射文件中statement的parameterType的值保持一致。
4. mapper接口的返回值类型要和mapper映射文件中statement的resultType值或resultMap中的type值保持一致。

可见如果想要做一些简单的操作，用这种模式最方便不过了。

接下来，需要修改User.xml文件为：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- 修改了namespace -->
<mapper namespace="com.pjhubs.dao.intf.UserMapper">
    <select id="selectUserWithID" parameterType="int" resultType="com.pjhubs.instance.User">
        select * from user where id = #{id}
    </select>
    <select id="selectAllUser" resultType="com.pjhubs.instance.User">
        select * from user
    </select>
    <insert id="insertUser" parameterType="com.pjhubs.instance.User">
        insert into user(nickname,passwd) values(#{nickname},#{passwd})
    </insert>
    <delete id="deleteUserWithID" parameterType="int">
        delete from user where id=#{id}
    </delete>
    <update id="updateUserWithNickname" parameterType="com.pjhubs.instance.User">
        update user set nickname=#{nickname} where id=#{id}
    </update>
</mapper>

创建一个新的UserMapper接口类，

import com.pjhubs.instance.User;

import java.util.List;

public interface UserMapper {

    public User selectUserWithID(int ID) throws Exception;
    public List<User> selectAllUser() throws Exception;
    public void insertUser(User user) throws Exception;
    public void deleteUserWithID(int ID) throws Exception;
    public void updateUserWithNickname(User user) throws Exception;

}

创建一个新的测试类，

import java.util.List;
import org.junit.jupiter.api.Test;

import com.pjhubs.instance.User;
import com.pjhubs.dao.intf.UserDAO;
import com.pjhubs.dao.impl.UserDAOImpl;

public class UserTest {

    @Test
    public void testSelectAllUser() throws Exception {
        UserDAO userDAO = new UserDAOImpl();
        List<User> userList = userDAO.selectAllUser();
        for (User user : userList) {
            System.out.println("id：" + user.getId() + "昵称：" + user.getNickname());
        }
    }

    @Test
    public void testSelectUserWithID() throws Exception {
        UserDAO userDAO = new UserDAOImpl();
        User user = userDAO.selectUserWithID(1);
        System.out.println("id:" + user.getId() + " 昵称:" + user.getNickname());
    }

    @Test
    public void testInsertUser() throws Exception {
        UserDAO userDAO = new UserDAOImpl();
        User user = new User();
        user.setNickname("PJHubs");
        user.setPasswd("woaiwoziji123");
        userDAO.insertUser(user);
    }

    @Test
    public void testDeleteUserByID() throws Exception {
        UserDAO userDAO = new UserDAOImpl();
        userDAO.deleteUserWithID(1);
    }

    @Test
    public void testUpdateUserNickname() throws Exception {
        UserDAO userDAO = new UserDAOImpl();
        User user = new User();
        user.setNickname("pjhubs");
        user.setId(1);
        user.setPasswd("woaiwoziji123");
        userDAO.updateUserWithNickname(user);
    }

}

2. 自己定义一个线程，每过5秒钟将当前系统的使用内存，用Log4j打印到磁盘和屏幕。
创建一个线程类，

package pjhubs;

import org.apache.log4j.Logger;

public class ThreadClass implements Runnable {
    private Thread t;
    private String threadName;

    ThreadClass( String name) {
        threadName = name;
        System.out.println("Creating " +  threadName );
    }

    public void run() {
        System.out.println("Running " +  threadName );
        while(true) {
            try {
                Thread.sleep(2000);
                Logger logger = Logger.getLogger(Main.class);
                logger.info("当前JVM已经从操作系统拿到的内存大小:"
                        + Runtime.getRuntime().totalMemory() / 1024 / 1024 + "M");
            } catch (InterruptedException e) {
                System.out.println("Thread " +  threadName + " interrupted.");
            }
            System.out.println("Thread " +  threadName + " exiting.");
        }
    }

    public void start () {
        System.out.println("Starting " +  threadName );
        if (t == null) {
            t = new Thread (this, threadName);
            t.start ();
        }
    }
}

在Main方法中进行调用，

public class Main {

    public static void main(String[] args) throws Exception {
        ThreadClass t1 = new ThreadClass("pjThread");
        t1.start();
    }
}