一文上手MyBatis

川长思鸟来 2024-04-18 15:10 78阅读 0赞

## 一文上手MyBatis ##

## 1 原生MyBatis ##

## 1.1 Maven导入依赖 ##

## 1.2 表结构 ##

CREATE TABLE `tbl_employee` (
      `id` int(11) NOT NULL AUTO_INCREMENT,
      `last_name` varchar(50) DEFAULT NULL,
      `email` varchar(50) DEFAULT NULL,
      `gender` int(11) DEFAULT NULL,
      `d_id` int(11) DEFAULT NULL,
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=1004 DEFAULT CHARSET=utf8;

## 1.3 实体 ##

public class Employee {
        private Integer id;
        private String lastName;
        private String email;
        private Integer gender;

## 1.4 配置 mybatis-config.xml 主配置文件 ##

在classpath下新建mybatis-config.xml文件

<?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/mytest" />
    				<property name="username" value="root" />
    				<property name="password" value="admin" />
    			</dataSource>
    		</environment>
    	</environments>
    	
    		<mappers>
    			<mapper resource="EmployeeMapper.xml" />
    		</mappers>
    	
    </configuration>

## 1.5 HelloWorld ##

## 1.5.1 配置mapper文件 ##

Classpath下新建 EmployeeMapper.xml文件

<?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 namespace="suibian">
    	
    	<select id="selectEmployee" 
    resultType="com.hongyu.mybatis.beans.Employee">
    		
    		select id, last_name lastName, email, gender from tbl_employee where id = #{id}
    	</select>
    </mapper>

## 1.5.2 后台测试方法 ##

@Test
        public void testSqlSessionFactory() throws IOException {
    
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory 
    = new SqlSessionFactoryBuilder().build(inputStream);
            System.out.println(sqlSessionFactory);
    
            SqlSession sqlSession = sqlSessionFactory.openSession();
            System.out.println(sqlSession);
    
            try {
    // 第一个参数就是唯一标识，即映射文件中的namespace.查询标签的ID
    // 第二个参数sql语句中的占位参数
                Employee employee = sqlSession.selectOne("suibian.selectEmployee", 1003);
                System.out.println(employee);
            }finally {
                sqlSession.close();
            }
        }

## 1.6 Mapper.xml文件与DAO结合使用 ##

## 1.6.1 说明 ##

在mybatis里，mapper就相当于是DAO的概念  
绑定Mapper.xml与DAO文件，namespace写成DAO的全类名，查询标签的id写成DAO中方法的名字。

## 1.6.2 EmployeeMapper.xml文件 ##

<?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 namespace="com.hongyu.mybatis.dao.EmployeeDao">
    	
    	
    	
    	<select id="getEmployeeById" 
    resultType="com.hongyu.mybatis.beans.Employee">
    		select id, last_name lastName, email, gender from tbl_employee where id = #{id}
    	</select>
    </mapper>

## 1.6.3 EmployeeDao接口 ##

package com.hongyu.mybatis.dao;
    import com.hongyu.mybatis.beans.Employee;
    public interface EmployeeDao {
        public Employee getEmployeeById(Integer id);
    }

## 1.6.4 后台测试方法 ##

@Test
        public void testMapperInterface() throws IOException {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            System.out.println(sqlSessionFactory);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            System.out.println(sqlSession);
            try {
                EmployeeDao dao = sqlSession.getMapper(EmployeeDao.class);
                Employee employee = dao.getEmployeeById(1003);
                System.out.println(employee);
            }finally {
                sqlSession.close();
            }
        }

## 1.7 mybatis-config.xml高级 ##

## 1.7.1 单独配置属性 ##

## 1.7.2 将数据库配置整个抽出去 ##

## 1.7.2.1 新建db.properties文件 ##

jdbc.driver=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/mytest
    jdbc.username=root
    jdbc.password=admin

## 1.7.2.2 修改mybatis配置文件 ##

## 1.7.3 设置项 ##

## 1.7.3.1 设置表名下划线，实体是驼峰命名法的映射 ##

<settings>
    		
    		<setting name="mapUnderscoreToCamelCase" value="true"/>
    	</settings>

false则不映射

## 1.7.4 设置别名 ##

## 1.7.4.1 设置某个类的别名 ##

<typeAliases>
    		
    		<typeAlias type="com.hongyu.mybatis.beans.Employee" alias="employee" />
    		
    	</typeAliases>

映射文件中直接使用别名

<select id="getEmployeeById" resultType="employee">
    		select id, last_name , email, gender from tbl_employee where id = #{id}
    	</select>

## 1.7.4.2 为某个包及子包下的类批量取默认别名 ##

<typeAliases>
    		
    		<package name="com.hongyu.mybatis.beans" />
    	</typeAliases>

如果不想用默认的别名，可以使用注解 @Alias(“employeeEntity”) 指定自定义别名，前提是必须配置 package包指定标签

import org.apache.ibatis.type.Alias;
    @Alias("employeeEntity")
    public class Employee {

## 1.7.5 mybatis预制了很多别名 ##

Mybatis已经为很多基本类型取好了别名，例如：map、hashmap、list、int、integer等等。  
建议使用全类名，比较清晰

## 1.7.6 批量声明映射文件 ##

批量声明要求Mapper.xml必须与DAO文件同位置，且同名

<mappers>
    		
    		<package name="com.hongyu.mybatis.dao" />
    	</mappers>

Dao文件改名为： com.hongyu.mybatis.dao.EmployeeMapper  
Mapper文件增加包名：com/hongyu/mybatis/dao/EmployeeMapper.xml

## 1.8 增、删、改的实现 ##

## 1.8.1 新增 ##

// 新建
    public void addEmployee(Employee employee);
    
    
    	<insert id="addEmployee" 
    parameterType="com.hongyu.mybatis.beans.Employee">
    		INSERT INTO tbl_employee(last_name, email, gender) VALUE (#{lastName}, #{email}, #{gender})
    	</insert>

## 1.8.2 更新 ##

// 修改
    public void updateEmployee(Employee employee);
    
    
    	<update id="updateEmployee" >
    		UPDATE tbl_employee SET last_name=#{lastName}, email=#{email}, gender=#{gender} WHERE id=#{id}
    	</update>

## 1.8.3 删除 ##

// 删除
        public void deleteEmployee(Integer id);
    
    
    	<delete id="deleteEmployee" >
    		DELETE FROM tbl_employee WHERE id=#{id}
    	</delete>

## 1.9 得到增、删、改操作的返回值 ##

修改DAO接口的返回值即可，Integer或boolean都可以
    // 新建
        public Integer addEmployee(Employee employee);
    
        // 修改
        public Integer updateEmployee(Employee employee);
    
        // 删除
        public Integer deleteEmployee(Integer id);

## 1.10 数据自增的数据，获得主键的值 ##

Insert标签中增加属性useGeneratedKeys、keyProperty就可以，keyProperty=”id” 这里的id是表的主键值，不是实体的

<insert id="addEmployee" parameterType="com.hongyu.mybatis.beans.Employee"
    		useGeneratedKeys="true" keyProperty="id"
    	>
    		INSERT INTO tbl_employee(last_name, email, gender) VALUE (#{lastName}, #{email}, #{gender})
    	</insert>

这样配置后，执行新增后，实体中就有id的值了

## 1.11 参数传递 ##

## 1.11.1 单个普通参数 ##

就是参数是1个，而且是基本类型，可以 \#\{随便写\}，因为mybatis不会进行任何处理。  
例如：

<select id="getEmployeeById" resultType="employeeEntity">
    		select id, last_name , email, gender from tbl_employee where id = #{aaa}
    	</select>

## 1.11.2 多个参数 ##

多个参数只允许 \#\{arg0\}, \#\{arg1\} 或 \#\{param1\}, \#\{param2\}

public Employee getEmployeeByIdAndLastName(Integer id, String lastName);
    
    
    	<select id="getEmployeeByIdAndLastName" resultType="employeeEntity">
    		select id, last_name , email, gender from tbl_employee where id = #{arg0} AND last_name=#{arg1}
    	</select>

## 1.11.3 命名参数 ##

就是对多个参数的优化，使用@Param注解

public Employee getEmployeeByIdAndLastName(@Param("id") Integer id, 
    @Param("lastName") String lastName);
    
    
    
    	<select id="getEmployeeByIdAndLastName" resultType="employeeEntity">
    		select id, last_name , email, gender from tbl_employee where id = #{id} AND last_name=#{lastName}
    	</select>

## 1.11.4 POJO参数 ##

直接写Entity的属性值就可以，参见1.8增删改

如果传了两个pojo，需要使用上一节的命名参数@Param注解，例如：emp，则参数写成 \#\{emp.id\}

## 1.11.5 Map参数 ##

参数按Map传的写

public Employee getEmployeeByMap(Map<String, Object> map);
    
    
    	<select id="getEmployeeByMap" resultType="employeeEntity">
    		select id, last_name , email, gender from tbl_employee where id = #{id} AND last_name=#{lastName}
    	</select>

测试程序：

Map<String, Object> map = new HashMap<>();
    map.put("id", 1003);
    map.put("lastName", "婷婷");
    Employee employee = dao.getEmployeeByMap(map);

## 1.11.6 List或Array参数 ##

也会封装成Map，数组的key是array，List的key是list  
\#\{array\} \#\{list\}

## 1.12 $\{\}的使用 ##

\#\{\} 是在sql中设置？，然后传入参数

是 直 接 替 换 s q l 语 句 中 的 地 方 ， \{\} 是直接替换sql语句中的地方， 是直接替换sql语句中的地方，\{\}可以写表名，也可以写字段名，这个是\#\{\}做不到的

## 1.13 高级查询 ##

## 1.13.1 查询多条记录返回List ##

// 查询多条语句返回List集合  
public List getEmps();

<select id="getEmps" resultType="employeeEntity">
    		select id, last_name , email, gender from tbl_employee
    	</select>

注意：即使返回的是List，但resultType需要填写List中对象的类型

## 1.13.2 查询1条记录返回Map ##

结果的Map，key是查询的字段名，value是值  
\{gender=1, last\_name=刚哥, id=1001, email=gg@1.com\}

// 查询1条记录返回Map集合
        public Map<String, Object> getEmpByIdReturnMap(Integer id);
    
    
    	<select id="getEmpByIdReturnMap" resultType="map" >
    		select id, last_name , email, gender from tbl_employee where id = #{id}
    	</select>

## 1.13.3 查询多条数据返回Map ##

需要借助注解@MapKey，指定Map的key

// 查询多条数据返回Map
        @MapKey("id")
        public Map<Integer, Employee> getEmpsReturnMap();
    
    
    	<select id="getEmpsReturnMap"
     resultType="com.hongyu.mybatis.beans.Employee">
    		select id, last_name , email, gender from tbl_employee
    	</select>

## 1.14 自定义映射 ##

## 1.14.1 单表 ##

public Employee getEmployeeById(Integer id);
    
    
    	<select id="getEmployeeById" resultMap="myEmp" >
    		select id, last_name , email, gender from tbl_employee where id = #{id}
    	</select>
    
    	<resultMap id="myEmp" type="com.hongyu.mybatis.beans.Employee" >
    		<id column="id" property="id" /> 
    		
    		<result column="last_name" property="lastName" />
    		<result column="email" property="email" />
    		<result column="gender" property="gender"/>
    	</resultMap>

## 1.14.2 表关联-级联写法 ##

在Employee实体中增加 Dept 引用属性

public Employee getEmpAndDept(Integer id);
    <select id="getEmpAndDept" resultMap="myEmpAndDept" >
    		SELECT e.id eid, e.last_name, e.email, e.gender, d.dept_id did, d.dept_name
    		FROM tbl_employee e JOIN tbl_dept d
    		ON  e.d_id=d.dept_id
    		WHERE e.id = #{id}
    	</select>
    	<resultMap id="myEmpAndDept" 
    type="com.hongyu.mybatis.beans.Employee" >
    		<id column="eid" property="id"></id>
    		<result column="last_name" property="lastName" />
    		<result column="email" property="email" />
    		<result column="gender" property="gender"/>
    		<result column="did" property="dept.deptId" />
    		<result column="dept_name" property="dept.deptName" />
    	</resultMap>

## 1.14.3 表关联-association写法 ##

## 1.14.4 分布查询 ##

先建一个部门的deptMapper，然后EmployeeMapper引用

import com.hongyu.mybatis.beans.Dept;
    public interface DeptMapperResultMap {
        public Dept getDeptById(Integer id);
    }
    
    <mapper namespace="com.hongyu.mybatis.dao.DeptMapperResultMap">
    	
    	<select id="getDeptById" resultType="com.hongyu.mybatis.beans.Dept" >
    		SELECT dept_id deptId, dept_name deptName FROM tbl_dept WHERE dept_id=#{id}
    	</select>
    </mapper>
    
    public Employee getEmpAndDeptStep(Integer id);
    <select id="getEmpAndDeptStep" resultMap="myEmpAndDeptStep">
    		SELECT id, last_name, email, gender, d_id
    		FROM tbl_employee
    		WHERE id=#{id}
    	</select>
    
    	<resultMap id="myEmpAndDeptStep" 
    type="com.hongyu.mybatis.beans.Employee" >
    		<id column="id" property="id" />
    		<result column="last_name" property="lastName" />
    		<result column="email" property="email" />
    		<result column="gender" property="gender"/>
    		
    	<association property="dept"		 select="com.hongyu.mybatis.dao.DeptMapperResultMap.getDeptById"
    		column="d_id" >
    		</association>
    
    	</resultMap>

## 1.14.5 分布查询-延迟加载 ##

在Mybatis全局配置文件中增加settings

<setting name="lazyLoadingEnabled" value="true" />
    
    <setting name="aggressiveLazyLoading" value="false" />

## 1.14.6 集合类型联合属性 ##

public Dept getDeptAndEmpsById(Integer id);
    
    <select id="getDeptAndEmpsById" resultMap="myDeptAndEmps" >
    		SELECT d.dept_id did, d.dept_name, e.id eid, e.last_name, e.email, e.gender
    		FROM tbl_dept d LEFT JOIN tbl_employee e
    		ON d.dept_id=e.d_id
    		WHERE d.dept_id=#{id}
    	</select>
    	<resultMap id="myDeptAndEmps" type="com.hongyu.mybatis.beans.Dept" >
    		<id column="did" property="deptId" />
    		<result column="dept_name" property="deptName" />
    		
    		<collection  property="emps" 
    ofType="com.hongyu.mybatis.beans.Employee" >
    			<id column="eid" property="id" />
    			<result property="lastName" column="last_name" />
    			<result property="email" column="email" />
    			<result property="gender" column="gender" />
    		</collection>
    	</resultMap>

## 1.14.7 Collection分布查询 ##

public List<Employee> getEmpsByDid(Integer did);
    
    <select id="getEmpsByDid" resultType="com.hongyu.mybatis.beans.Employee" >
    		SELECT id, last_name lastName, email, gender
    		FROM tbl_employee
    		WHERE d_id=#{did}
    	</select>
    
    public Dept getDeptAndEmpsByIdStep(Integer id);
    
    <select id="getDeptAndEmpsByIdStep" resultMap="myDeptAndEmpsStep" >
    		SELECT dept_id did, dept_name
    		FROM tbl_dept
    		WHERE dept_id=#{id}
    	</select>
    	<resultMap  id="myDeptAndEmpsStep" 
    type="com.hongyu.mybatis.beans.Dept" >
    		<id column="did" property="deptId" />
    		<result column="dept_name" property="deptName" />
    			<collection property="emps"
    					select="com.hongyu.mybatis.dao.EmployeeMapperResultMap.getEmpsByDid"
    					column="did" >
    		</collection>
    	</resultMap>

## 1.14.8 分布查询传多列值 ##

传参时采用 \{k1=v1, k2=v2\} 的形式  
Key是 参数占位的名字，即 \#\{k1\}  
Value是sql中对应的值

## 1.14.9 单独设置是否延迟加载 ##

collection 标签 和 association 标签 都有 fetchType 属性  
fetchType=“eager” 不延迟加载  
fetchType=“lazy” 延迟加载

## 1.15 可重用sql片段 ##

<sql id="empSelect" >
    		select id, last_name , email, gender
    	</sql>
    
    	
    	<select id="getEmployeeById" resultMap="myEmp" >
    		<include refid="empSelect" /> from tbl_employee where id = #{id}
    	</select>

## 1.16 动态SQL ##

## 1.16.1 Where if ##

Where 标签主要是解决了第一个and的问题

public List<Employee> getEmpsByConditionIfWhere(Employee condition);
    
    <select id="getEmpsByConditionIfWhere" resultMap="myEmp" >
    		SELECT id, last_name lastName, email, gender FROM tbl_employee
    		<where>
    		<if test="id!=null">
    			AND id=#{id}
    		</if>
    		<if test="lastName!=null&&lastName!=""">
    			AND last_name=#{lastName}
    		</if>
    		<if test="email!=null and email.trim()!=''">
    			AND email=#{email}
    		</if>
    		<if test="gender==0 or gender==1" >
    			AND gender=#{gender}
    		</if>
    		</where>
    	</select>

## 1.16.2 trim的使用 ##

<select id="getEmpsByConditionTrim" resultMap="myEmp" >
    		SELECT id, last_name , email, gender FROM tbl_employee
    
    		
    		<trim prefix=" where " prefixOverrides="and" suffix="" suffixOverrides="">
    			<if test="id!=null">
    				AND id=#{id}
    			</if>
    			<if test="lastName!=null&&lastName!=""">
    				AND last_name=#{lastName}
    			</if>
    			<if test="email!=null and email.trim()!=''">
    				AND email=#{email}
    			</if>
    			<if test="gender==0 or gender==1" >
    				AND gender=#{gender}
    			</if>
    		</trim>
    	</select>

## 1.16.3 set ##

主要解决多出的逗号的问题

update table
    <set>
    	<if test=”XXX”>
    		XXX = #{XXX} ,
    	</if>
    	<if test=”XXX”>
    		XXX = #{XXX} ,
    	</if>
    	<if test=”XXX”>
    		XXX = #{XXX} 
    	</if>
    <set>

## 1.16.4 choose when otherwise ##

相当于case when，满足条件则不往下执行

otherwise 是最后的默认条件

## 1.16.5 foreach ##

public List<Employee> getEmpsByIds(@Param("ids") List<Integer> ids);
    <select id="getEmpsByIds" resultMap="myEmp">
    		SELECT id, last_name , email, gender FROM tbl_employee
    		WHERE id IN
    			
    			<foreach collection="ids" item="currId" open="(" close=")" separator=",">
    				#{currId}
    			</foreach>
    	</select>

也可以完成批准添加、批量修改、批量删除

## 2 Mybatis SpringMVC Spring 整合 ##

## 2.1 下载整合适配包 ##

Mybatis-Spring		Mybatis			Spring
    1.0.0/1.0.1			3.0.1-3.0.5		3.0.0+
    1.0.2				3.0.6			3.0.0+
    1.1.0+				3.1.0+			3.0.0+
    1.3.0+				3.4.0+			3.0.0+

学习教程：  
http://www.mybatis.org/spring/zh/index.html

## 2.2 导入jar包 ##

<dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
          <version>3.4.6</version>
        </dependency>
    
        
        <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <version>5.1.38</version>
        </dependency>
    
        
        <dependency>
          <groupId>log4j</groupId>
          <artifactId>log4j</artifactId>
          <version>1.2.17</version>
        </dependency>
    
        
        <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-webmvc</artifactId>
          <version>4.3.18.RELEASE</version>
        </dependency>
    <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-jdbc</artifactId>
          <version>4.3.18.RELEASE</version>
        </dependency>
        <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-tx</artifactId>
          <version>4.3.18.RELEASE</version>
        </dependency>
        
        <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>jstl</artifactId>
          <version>1.2</version>
        </dependency>
    
        
        <dependency>
          <groupId>com.fasterxml.jackson.core</groupId>
          <artifactId>jackson-databind</artifactId>
          <version>2.7.0</version>
        </dependency>
        
        <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>servlet-api</artifactId>
          <version>2.5</version>
          <scope>provided</scope>
        </dependency>
    
        <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>jsp-api</artifactId>
          <version>2.0</version>
          <scope>provided</scope>
        </dependency>
    
        
        <dependency>
          <groupId>commons-fileupload</groupId>
          <artifactId>commons-fileupload</artifactId>
          <version>1.3.1</version>
        </dependency>
    
        <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis-spring</artifactId>
          <version>1.3.0</version>
    </dependency>
    
        <dependency>
          <groupId>com.mchange</groupId>
          <artifactId>c3p0</artifactId>
          <version>0.9.5.2</version>
        </dependency>

## 2.3 配置web.xml ##

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
             version="3.1">
    
      
      <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <init-param>
          <param-name>encoding</param-name>
          <param-value>UTF-8</param-value>
        </init-param>
      </filter>
      <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
      </filter-mapping>
    
      
      <filter>
        <filter-name>HiddenHttpMethodFilter</filter-name>
        <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
      </filter>
      <filter-mapping>
        <filter-name>HiddenHttpMethodFilter</filter-name>
        <url-pattern>/*</url-pattern>
      </filter-mapping>
    
      
      <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
      </context-param>
    
      <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
      </listener>
    
      
      <servlet>
        <servlet-name>springDispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
          <param-name>contextConfigLocation</param-name>
          <param-value>classpath:springmvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
      </servlet>
      <servlet-mapping>
        <servlet-name>springDispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
      </servlet-mapping>
    </web-app>

## 2.4 配置SpringMVC文件 ##

## 2.5 配置 db.properties 文件 ##

jdbc.driver=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/mytest
    jdbc.username=root
    jdbc.password=admin

## 2.6 配置log4j ##

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
     
    <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
     
     <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
       <param name="Encoding" value="UTF-8" />
       <layout class="org.apache.log4j.PatternLayout">
        <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) \n" />
       </layout>
     </appender>
     <logger name="java.sql">
       <level value="debug" />
     </logger>
     <logger name="org.apache.ibatis">
       <level value="info" />
     </logger>
     <root>
       <level value="debug" />
       <appender-ref ref="STDOUT" />
     </root>
    </log4j:configuration>

## 2.7 配置 mybatis-config.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>
    
    	
    	<settings>
    		
    		<setting name="mapUnderscoreToCamelCase" value="true"/>
    		
    		<setting name="lazyLoadingEnabled" value="true" />
    		
    		<setting name="aggressiveLazyLoading" value="false" />
    	</settings>
    </configuration>

## 2.8 配置Spring配置文件 ##

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:context="http://www.springframework.org/schema/context"
           xmlns:tx="http://www.springframework.org/schema/tx"
           xmlns:mybatis-spring="http://mybatis.org/schema/mybatis-spring"
           xsi:schemaLocation="http://mybatis.org/schema/mybatis-spring http://mybatis.org/schema/mybatis-spring-1.2.xsd
    		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd
    		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">
        
        <context:component-scan base-package="com.hongyu.ssm" >
            <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller" />
        </context:component-scan>
    
        
        
        <context:property-placeholder location="classpath:db.properties" />
        <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
            <property name="driverClass" value="${jdbc.driver}" />
            <property name="jdbcUrl" value="${jdbc.url}" />
            <property name="user" value="${jdbc.username}" />
            <property name="password" value="${jdbc.password}" />
        </bean>
    
        
        <bean id="dataSourceTransactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
            <property name="dataSource" ref="dataSource" />
        </bean>
    
        
        <tx:annotation-driven transaction-manager="dataSourceTransactionManager"/>
    
        
        
        <bean class="org.mybatis.spring.SqlSessionFactoryBean" >
            <property name="dataSource" ref="dataSource" />
            
            <property name="configLocation" value="classpath:mybatis-config.xml" />
            
            <property name="mapperLocations" value="classpath:com/hongyu/ssm/dao/*.xml" />
            
            <property name="typeAliasesPackage" value="com.hongyu.ssm.beans" />
        </bean>
        
        <mybatis-spring:scan base-package="com.hongyu.ssm.dao" />
    
    </beans>

## 2.9 使用mybatis的DAO文件 ##

@RestController
    public class EmployeeAction {
    
        @Autowired
        private EmployeeMapper employeeMapper;
    
        @RequestMapping("/emp/{id}")
        public Employee getEmployeeById(@PathVariable("id") int id) {
            return employeeMapper.getEmployeeById(id);
        }

## 3 遇到的坑 ##

坑：Spring文件中配置事务，导致服务无法正常启动  
解决：Spring的命名空间问题，修改了Spring配置文件的头文件，问题解决