maven 构建项目
1. 添加依赖
spring-webmvc
mybatis
mysql-connector-java
mybatis-spring
junit
pom.xml 文件内容如下：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <project xmlns="http://maven.apache.org/POM/4.0.0" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> 5 <parent> 6 <artifactId>springStudy</artifactId> 7 <groupId>org.example</groupId> 8 <version>1.0-SNAPSHOT</version> 9 </parent> 10 <modelVersion>4.0.0</modelVersion> 11 12 <artifactId>mybatis-01</artifactId> 13 14 <properties> 15 <maven.compiler.source>8</maven.compiler.source> 16 <maven.compiler.target>8</maven.compiler.target> 17 </properties> 18 19 <dependencies> 20 21 <dependency> 22 <groupId>org.springframework</groupId> 23 <artifactId>spring-webmvc</artifactId> 24 <version>5.3.7</version> 25 </dependency> 26 27 <dependency> 28 <groupId>org.mybatis</groupId> 29 <artifactId>mybatis</artifactId> 30 <version>3.4.6</version> 31 </dependency> 32 33 <dependency> 34 <groupId>mysql</groupId> 35 <artifactId>mysql-connector-java</artifactId> 36 <version>5.1.49</version> 37 </dependency> 38 39 <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis-spring --> 40 <dependency> 41 <groupId>org.mybatis</groupId> 42 <artifactId>mybatis-spring</artifactId> 43 <version>1.3.2</version> 44 </dependency> 45 <dependency> 46 <groupId>junit</groupId> 47 <artifactId>junit</artifactId> 48 <version>RELEASE</version> 49 <scope>test</scope> 50 </dependency> 51 52 </dependencies> 53 54 <build> 55 <!-- 定义classpath --> 56 <resources> 57 <!-- resources文件 --> 58 <resource> 59 <directory>src/main/resources</directory> 60 <!-- 是否被过滤,如果被过滤则无法使用 --> 61 <filtering>false</filtering> 62 </resource> 63 <!-- java文件夹 --> 64 <resource> 65 <directory>src/main/java</directory> 66 <!-- 引入映射文件等 --> 67 <includes> 68 <include>**/*.xml</include> 69 <include>**/*.properties</include> 70 </includes> 71 </resource> 72 </resources> 73 </build> 74 75 </project>
其中<build><resource>中内容为过滤项目中 xml 文件和 properties 文件的设置，否则运行时项目中 xml 文件或 properties 文件会加载不到。
2. 创建实体类
以 User 为例，代码如下：
1 package com.xsmile.pojo; 2 3 import java.util.List; 4 5 public class User { 6 private int id; 7 private String name; 8 private String password; 9 10 public User() { 11 } 12 13 public User(int id, String name, String password) { 14 this.id = id; 15 this.name = name; 16 this.password = password; 17 } 18 19 public int getId() { 20 return id; 21 } 22 23 public void setId(int id) { 24 this.id = id; 25 } 26 27 public String getName() { 28 return name; 29 } 30 31 public void setName(String name) { 32 this.name = name; 33 } 34 35 public String getPassword() { 36 return password; 37 } 38 39 public void setPassword(String password) { 40 this.password = password; 41 } 42 43 @Override 44 public String toString() { 45 return "User{" + 46 "id=" + id + 47 ", name=‘" + name + ‘\‘‘ + 48 ", password=‘" + password + ‘\‘‘ + 49 ‘}‘; 50 } 51 }
3. 数据库准备
创建项目使用的数据库如 mybatis，User 对应的表 user。如图所示，实体类中变量名与数据库中列明一一对应。
4. 配置mybatis-config文件
通用模板，只需根据自身数据库、表、用户名及密码进行修改即可。
1 <?xml version="1.0" encoding="UTF-8" ?> 2 <!DOCTYPE configuration 3 PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 4 "http://mybatis.org/dtd/mybatis-3-config.dtd"> 5 <configuration> 6 <environments default="development"> 7 <environment id="development"> 8 <transactionManager type="JDBC"/> 9 <dataSource type="POOLED"> 10 <property name="driver" value="com.mysql.jdbc.Driver"/> 11 <property name="url" value="jdbc:mysql://localhost:3306/mybatis?characterEncoding=UTF-8"/> 12 <property name="username" value="root"/> 13 <property name="password" value="xjw123456"/> 14 </dataSource> 15 </environment> 16 </environments> 17 <mappers> 18 <mapper resource="com/xsmile/dao/UserMapper.xml"/> 19 </mappers> 20 </configuration>
值得注意的是最后 <mapper> resource 中需要添加指定的接口实现类 xml 文件
5. 创建接口UserMapper
接口包含查询方法，获取表中所有用户信息。
1 public interface UserMapper { 2 public List<User> getUsers(); 3 }
6. 创建实现类
实现类转由 xml 文件进行配置实现
1 <?xml version="1.0" encoding="UTF-8" ?> 2 <!DOCTYPE mapper 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> 5 <mapper namespace="com.xsmile.dao.UserMapper"> 6 <select id="getUsers" resultType="com.xsmile.pojo.User"> 7 select * from user 8 </select> 9 </mapper>
命名空间 namespace 指向接口全路径，id 为要实现接口的方法名对应，resultType 为结果对象全类名的形式。
7. sqlSession 工具类
由于 sqlSession 代码统一，编写为一个工具类，方便以后使用。
1 package com.xsmile.util; 2 3 import org.apache.ibatis.io.Resources; 4 import org.apache.ibatis.session.SqlSession; 5 import org.apache.ibatis.session.SqlSessionFactory; 6 import org.apache.ibatis.session.SqlSessionFactoryBuilder; 7 8 import java.io.IOException; 9 import java.io.InputStream; 10 11 public class MybatisUtil { 12 private static SqlSessionFactory sqlSessionFactory; 13 static { 14 String resource = "mybatis-config.xml"; 15 InputStream inputStream; 16 try { 17 inputStream = Resources.getResourceAsStream(resource); 18 sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 19 } catch (IOException e) { 20 e.printStackTrace(); 21 } 22 } 23 24 25 public static SqlSession getSqlSession(){ 26 return sqlSessionFactory.openSession(); 27 } 28 29 }
后续使用只需调用类方法即可获取 sqlSession，即：
MybatisUtil.getSqlSession()
8. 编写测试类
1 package com.xsmile.dao; 2 3 import com.xsmile.pojo.User; 4 import com.xsmile.util.MybatisUtil; 5 import org.apache.ibatis.session.SqlSession; 6 import org.junit.Test; 7 8 import java.util.List; 9 10 public class UserMapperTest { 11 12 @Test 13 public void test(){ 14 15 SqlSession sqlSession = MybatisUtil.getSqlSession(); 16 17 UserMapper mapper = sqlSession.getMapper(UserMapper.class); 18 19 List<User> users = mapper.getUsers(); 20 21 for (User user : users) { 22 System.out.println(user); 23 } 24 25 26 } 27 }
其中 sqlSession.getMapper() 为官方推荐方法,它不依赖于字符串字面值，会更安全一点。另外方法如：
List<User> users1 = sqlSession.selectList("com.xsmile.dao.UserMapper.getUsers");
执行结果如下：
1 User{id=1, name=‘xsmile‘, password=‘123456‘} 2 User{id=2, name=‘sophia‘, password=‘123456‘} 3 User{id=3, name=‘alex‘, password=‘123456‘} 4 User{id=4, name=‘jerry‘, password=‘123456‘} 5 User{id=5, name=‘俊伟君‘, password=‘123456‘}