SSM(Spring+Spring MVC+MyBatis)学习之路——MyBatis增删改查

1.用eclipse创建动态web项目，命名为mybatis

2.右键mybatis项目，选择Build Path, Configure Build Path…

3.导入相关的jar包，点击Add External JARS, 把这三个jar包导入后，最后点击Apply。需导入的jar包如下：

log4j-1.2.17.jar;
mybatis-3.4.1.jar;
mysql-connector-java-6.0.6.jar

另外原项目与jar包我已保存到了网盘，方便下载与学习:
https://pan.baidu.com/s/1WRysIDE-DcbyQA-Jogu2lQ 密码: xjkc

4.项目结构

5.相关Java类与XML文件

（1）Book.java

构建一个POJO对象：

package com.edu.mybatis.pojo;

public class Book {

    int id;
    String bookName;
    String author;
    float price;
    String description;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getBookName() {
        return bookName;
    }
    public void setBookName(String bookName) {
        this.bookName = bookName;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }


}

(2)BookMapper.java

采用XML方式构建映射器，它包含一个接口和一个XML。

package com.edu.mybatis.mapper;

import java.util.List;

import com.edu.mybatis.pojo.Book;

public interface BookMapper {
    public int insertBook(Book book);  //新增
    public int deleteBook(int id);     //删除
    public int updateBook(Book book);  //更改
    public Book getBook(int id);    //获取书籍信息
    public List findBooks(String bookName);//同名书籍列表
}

(3)BookMapper.xml

"1.0" encoding="UTF-8"?>
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
    "http://mybatis.org//dtd/mybatis-3-mapper.dtd">
namespace="com.edu.mybatis.mapper.BookMapper">

    "insertBook" parameterType="book">
        insert into t_book(book_id, book_name, book_author, book_price, book_description) values(#{id}, #{bookName}, #{author}, #{price}, #{description})
    

    "deleteBook" parameterType="int">
        delete from t_book where book_id= #{id}
    

    "updateBook" parameterType="book">
        update t_book set book_name = #{bookName}, book_author = #{author}, book_price = #{price}, book_description = #{description} where book_id= #{id}
    

    <select id="getBook" parameterType="int" resultType="book">
        select book_id as id, book_name as name, book_author as author, book_price as price, book_description as description from t_book where book_id= #{id}
    select>

    <select id="findBooks" parameterType="string" resultType="book">
        select book_id as id, book_name as bookName, book_author as author, book_price as price, book_description as description from t_book where book_name like concat('%', #{bookName}, '%')
    select>

XML文件里面的元素id标识了对应的SQL,parameterType标出了是什么类型的参数，resultType则代表结果映射为什么类型。其中insert、delete和update返回的是影响条数。

(4)SqlSessionFactoryUtils.java

通过SqlSessionFactoryBuilder来构建SqlSessionFactory，由于SqlSessionFactory应该采用单例模式，所以使用单例模式构建它。

package com.edu.mybatis.utils;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class SqlSessionFactoryUtils {
    private final static Class LOCK = SqlSessionFactoryUtils.class;

    private static SqlSessionFactory sqlSessionFactory = null;

    private SqlSessionFactoryUtils() {}

    public static SqlSessionFactory getSqlSessionFactory() {
        synchronized (LOCK) {

            if (sqlSessionFactory != null) {
                return sqlSessionFactory;
            }

            String resource = "mybatis-config.xml";
            InputStream inputStream;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            } 
            return sqlSessionFactory;
        }
    }

    public static SqlSession openSqlSession() {
        if(sqlSessionFactory == null) {
            getSqlSessionFactory();
        }
        return sqlSessionFactory.openSession();
    }
}

构造方法中加入了private关键字，使得其他代码不能通过new的方式来创建它。而加入synchronized关键字加锁，主要是为了防止在多线程中多次实例化SqlSessionFactory对象，从而保证SqlSessionFactory的唯一性。而openSqlSession方法的作用则是创建SqlSession对象

(5)mybatis-config.xml配置文件

<configuration>
    <typeAliases>
        <typeAlias alias="book" type="com.edu.mybatis.pojo.Book"/>
    typeAliases>
    
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC&useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            dataSource>
        environment>
    environments>
    <mappers>
        <mapper resource="com/edu/mybatis/mapper/BookMapper.xml"/>
    mappers>
configuration>

(6)log4j.properties日志文件配置

log4j.rootLogger=debug,stdout,logfile
### \u628A\u65E5\u5FD7\u4FE1\u606F\u8F93\u51FA\u5230\u63A7\u5236\u53F0 ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
#log4j.appender.stdout.Target=System.err
log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout

### \u628A\u65E5\u5FD7\u4FE1\u606F\u8F93\u51FA\u5230\u6587\u4EF6\uFF1Ajbit.log ###
log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=jbit.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %F %p %m%n
###\u663E\u793ASQL\u8BED\u53E5\u90E8\u5206
log4j.logger.com.ibatis=DEBUG
log4j.logger.com.ibatis.common.jdbc.SimpleDataSource=DEBUG
log4j.logger.com.ibatis.common.jdbc.ScriptRunner=DEBUG
log4j.logger.com.ibatis.sqlmap.engine.impl.SqlMapClientDelegate=DEBUG
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

(7)Main.java

编写运行代码Main，如下：

package com.edu.mybatis.main;

import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;

import com.edu.mybatis.mapper.BookMapper;
import com.edu.mybatis.utils.SqlSessionFactoryUtils;
import com.edu.mybatis.pojo.Book;

public class Main {

    public static void main(String[] args) {
        Logger log = Logger.getLogger(Main.class);
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            BookMapper bookMapper = sqlSession.getMapper(BookMapper.class);
            //新增
//          Book book = new Book();
//          book.setId(6);
//          book.setBookName("荷塘月色");
//          book.setAuthor("zhu");
//          book.setPrice(33.32f);
//          book.setDescription("I like the moon.");
//          bookMapper.insertBook(book);
            //删除
            //int book = bookMapper.deleteBook(6);
            //修改
//          Book book = bookMapper.getBook(6);
//          book.setBookName("青春飞扬");
//          book.setAuthor("帅哥");
//          book.setPrice(66.35f);
//          book.setDescription("青春不流逝");
//          bookMapper.updateBook(book);
            //查询所有同名书籍
            List bookList = bookMapper.findBooks("cool");
            for(Book book:bookList) {
                log.info(book.getBookName());
                log.info(book.getAuthor());
                log.info(book.getPrice());
                log.info(book.getDescription());
            }
            sqlSession.commit(); //注意增删改，需要commit,否则无效

            //System.out.println(book.getAuthor());
            //log.info(book.getAuthor());
        } finally {
            if(sqlSession != null) {
                sqlSession.close();
            }
        }
    }

}

通过SqlSession获取了一个RoleMapper接口对象，然后通过findBooks方法获取对象,最后正确关闭SqlSession对象。

(8)使用MySQL数据库，需要自行安装
建立t_book表:

t_book表内容（自定义）：

6.以Java Application的形式运行Main.java, 控制台打印日志如下：

DEBUG - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - Opening JDBC Connection
DEBUG - Created connection 900008524.
DEBUG - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@35a50a4c]
DEBUG - ==>  Preparing: select book_id as id, book_name as bookName, book_author as author, book_price as price, book_description as description from t_book where book_name like concat('%', ?, '%') 
DEBUG - ==> Parameters: cool(String)
DEBUG - <==      Total: 2
INFO - cool
INFO - wfe
INFO - 43.0
INFO - few
INFO - cool
INFO - haha
INFO - 66.0
INFO - hhh
DEBUG - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@35a50a4c]
DEBUG - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@35a50a4c]
DEBUG - Returned connection 900008524 to pool.

通过log4j.properties文件配置，让MyBatis打印其运行过程的轨迹。可以清晰地看到日志打印出来的SQL，SQL参数，以及返回的结果数。这样有利于监控MyBatis的运行过程和定位问题的所在。