一、配置环境：
首先我们需要Maven环境;
源码：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>sanzhongfangfa24_7_23</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<!--MySQL框架-->
<dependency>
<groupId>mysql</groupId>
<artifactId>
mysql-connector-java
</artifactId>
<version>
8.0.33
</version>
</dependency>
<!--日志框架-->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>
1.2.12
</version>
</dependency>
<!--MyBatis的框架-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.5</version>
</dependency>
<!--Java 单元测试框架用来@Test-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<dependency>
<!--用来指定上面的依赖进行测试两个缺一不可-->
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<version>RELEASE</version>
<scope>compile</scope>
</dependency>
</dependencies>
</project>
其次我们要配置核心配置文件;
这个文件是我们整个功能的基础；
源码:
<?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 >
<!-- 这是转Data类型的调用-->
<typeHandlers>
<typeHandler handler="org.handle.DateTypeHandler"></typeHandler>
</typeHandlers>
<environments default="develop">
<environment id="develop">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/duobiaochaxun?characterEncoding=utf-8"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mapper/duoduiduoMapper.xml"/>
<!-- <mapper resource="mapper/oneduiduoMapper.xml"/>-->
<!-- 必须配套写完不然报错 <mapper resource="mapper/UserMapper.xml"/>-->
</mappers>
</configuration>
第三我们要写日志的配置文件：
日志源码：
#日志
log4j.rootLogger=debug, stdout,R
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
# Pattern to output the caller's file name and line number.
Log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=example.log
Log4j.appender.R.MaxFileSize=100KB
# Keep one backup file
log4j.appender.R.MaxBackupIndex=5
log4j.appender.R.layout=org.apache.log4j.PatternLayout
Log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n
第四我们写数据库和Java对象类型的转化：
package org.handle;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
public class DateTypeHandler extends BaseTypeHandler<Date> {
// 将java类型转换成数据库需要的类型
@Override
//这段代码是 MyBatis 中的一个自定义类型处理器 (TypeHandler) 的一部分，它负责将Date对象转换为可以存储在数据库中的形式。
//具体来说，这个方法将 Date 对象转换为长整型 (long) 值，代表从 1970 年 1 月 1 日 00:00:00 UTC 开始到给定日期的毫秒数。
public void setNonNullParameter(PreparedStatement preparedStatement, int i, Date date, JdbcType jdbcType) throws SQLException {
//将日期赋值给long形的time
long time = date.getTime();
// PreparedStatement 的 setLong 方法将 time 设置到预编译 SQL 语句的第 i 个参数位置
//这意味着日期将作为长整型值被存储在数据库中。
preparedStatement.setLong(i, time);
}
// 将数据库中的类型 转换为java类型
// string 要转换的字符串
// resultSet 查询出的结果
@Override
// 将数据库查询结果中的长整型值转换为 java.util.Date 对象。
public Date getNullableResult(ResultSet resultSet, String s) throws SQLException {
// 这一行代码调用了 ResultSet 的 getLong 方法，根据列名 s 获取长整型值。
long along = resultSet.getLong(s);
//这一行代码使用从 ResultSet 中获取的长整型值创建一个新的 java.util.Date 对象。
Date date = new Date(along);
return date;
}
// 将数据库中的类型 转换为java类型
@Override
public Date getNullableResult(ResultSet resultSet, int i) throws SQLException {
long along = resultSet.getLong(i);
Date date = new Date(along);
return date;
}
// 将数据库中的类型 转换为java类型
@Override
//用于将从 CallableStatement 中获取的长整型值转换为 java.util.Date 对象
//这是一个 CallableStatement 对象，用于执行 SQL 存储过程或函数，并获取其结果。
public Date getNullableResult(CallableStatement callableStatement, int i) throws SQLException {
long aLong = callableStatement.getLong(i);
Date date = new Date(aLong);
return date;
}
}
这样我们就能将数据库和Java类型的的数据互相转化，别忘了将 该完成的类添加到核心配置文件里；
做完上述的环境配置，我们就要开始写项目和功能 。
二、写数据：
我们要写我们需要的Javabean数据，这个按照数据库来写，这里只展示功能，下面是我的例子。
数据库的表：
orders（订单表）：
user（用户表）：
Javabean的数据：
订单表：
package org.Emp;
import java.util.Date;
import java.util.List;
public class order {
private Integer id;
private Date ordertime;
private Double total;
private Integer uuid;
private user user;
public order() {
}
public order(Integer id, Date ordertime, Double total, Integer uuid, user user) {
this.id = id;
this.ordertime = ordertime;
this.total = total;
this.uuid = uuid;
this.user = user;
}
/**
* 获取
* @return id
*/
public Integer getId() {
return id;
}
/**
* 设置
* @param id
*/
public void setId(Integer id) {
this.id = id;
}
/**
* 获取
* @return ordertime
*/
public Date getOrdertime() {
return ordertime;
}
/**
* 设置
* @param ordertime
*/
public void setOrdertime(Date ordertime) {
this.ordertime = ordertime;
}
/**
* 获取
* @return total
*/
public Double getTotal() {
return total;
}
/**
* 设置
* @param total
*/
public void setTotal(Double total) {
this.total = total;
}
/**
* 获取
* @return uuid
*/
public Integer getUuid() {
return uuid;
}
/**
* 设置
* @param uuid
*/
public void setUuid(Integer uuid) {
this.uuid = uuid;
}
/**
* 获取
* @return user
*/
public user getUser() {
return user;
}
/**
* 设置
* @param user
*/
public void setUser(user user) {
this.user = user;
}
public String toString() {
return "order{id = " + id + ", ordertime = " + ordertime + ", total = " + total + ", uuid = " + uuid + ", user = " + user + "}";
}
}
用户表：
package org.Emp;
import java.util.Date;
import java.util.List;
public class user {
private Integer id;
private String username;
private String password;
private Date birthday;
public user() {
}
public user(Integer id, String username, String password, Date birthday) {
this.id = id;
this.username = username;
this.password = password;
this.birthday = birthday;
}
/**
* 获取
* @return id
*/
public Integer getId() {
return id;
}
/**
* 设置
* @param id
*/
public void setId(Integer id) {
this.id = id;
}
/**
* 获取
* @return username
*/
public String getUsername() {
return username;
}
/**
* 设置
* @param username
*/
public void setUsername(String username) {
this.username = username;
}
/**
* 获取
* @return password
*/
public String getPassword() {
return password;
}
/**
* 设置
* @param password
*/
public void setPassword(String password) {
this.password = password;
}
/**
* 获取
* @return birthday
*/
public Date getBirthday() {
return birthday;
}
/**
* 设置
* @param birthday
*/
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String toString() {
return "user{id = " + id + ", username = " + username + ", password = " + password + ", birthday = " + birthday + "}";
}
// private List<role> role;
//private List<order> order;
}
底层数据建成完毕，我们就要开始着手写功能;
三、写功能：
1、一对一查询
修改底层Javabean：
因为我们有两张表要查，要输出，但是Java输出形式只能是一张表，所以我们要用注入的方式，将用户表注入到订单表里，这样只用输出订单格式就可以了。
写Mapper映射（核心）：
我们要创建一个.xml的文件；
代码：
<?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">
<!--这一行定义了这个映射文件的命名空间，org.dao.oneselMapper 是一个唯一的标识符，用来区分不同的映射文件-->
<mapper namespace="org.dao.oneselMapper">
<!--这个 <resultMap> 元素定义了一个名为 orderMap 的映射规则，它会把查询结果映射到 org.Emp.order类型的对象上。-->
<!--也就是将数据库的值映射到Javabean中-->
<resultMap id="orderMap" type="org.Emp.order">
<!--id映射-->
<!--这一行指定了数据库中的 id 列与 JavaBean 中的 id 属性相对应。-->
<id column="id" property="id"></id>
<!--普通属性映射，这些 <result> 标签分别指定了数据库中的 ordertime, total, 和 uuid 列与 JavaBean 中对应的属性相对应。-->
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
<result column="uuid" property="uuid"></result>
<!--关联映射 (Association):-->
<!--这部分定义了一个一对一关联映射，表示 org.Emp.order 类中的 user 属性应该如何从数据库结果中获取其属性值。
这里，<association> 标签内的 <id> 和 <result> 标签指定了 user 表中的列名与 org.Emp.user 类中的属性名之间的对应关系。-->
<association property="user" javaType="org.Emp.user">
<id column="uuid" property="id"></id>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
</association>
</resultMap>
<!--数据库的一对一查询-->
<!--SQL 查询定义:-->
<!--这个 <select> 标签定义了一个 SQL 查询，使用前面定义的 orderMap 映射规则来映射查询结果。
这里的 SQL 语句选取了所有列 (select *) 并通过 o.uuid = u.id 条件进行表连接。-->
<select id="findall" resultMap="orderMap">
select * from orders o, user u where o.uuid = u.id
</select>
</mapper>
将映射文件配置到核心文件里：
最后，我们需要一个接口将写好的映射文件调用出来：
在映射文件中：
在接口中： 
这样我们的整个功能写完了，现在需要写一个测试方法来调用：
测试类：
首先要配置日志文件：
其次要加载MyBatis配置文件
代码：
public class testuser {
private InputStream in;
private SqlSessionFactory factory;
private SqlSession session;
@Test
public void star1() throws IOException {
//配置日志信息
Properties properties = new Properties();
FileInputStream fileInputStream = new FileInputStream("src/main/resources/config/log4j.properties");
properties.load(fileInputStream);
PropertyConfigurator.configure(properties);
// 加载 MyBatis 配置文件
//从类路径中获取 MyBatis 配置文件 mybatis-config.xml 的输入流。
in = Resources.getResourceAsStream("config/mybatis-config.xml");
//创建 SqlSessionFactory 对象，它是 MyBatis 的工厂类，用于创建 SqlSession。
factory = new SqlSessionFactoryBuilder().build(in);
//创建一个新的 SqlSession 实例，用于执行 SQL 语句。
session = factory.openSession();
//通过 SqlSession 获取 oneselMapper 接口的代理实现。
oneselMapper mapper = session.getMapper(oneselMapper.class);
//接口中定义了一个名为 sanbiaoall 的方法，该方法返回一个 List<students> 类型的列表。
List<order> findall = mapper.findall();
for (order a : findall) {
System.out.println(a);
}
}
}
结果：
Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
Opening JDBC Connection
Created connection 2101636817.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7d446ed1]
==> Preparing: select * from orders o, user u where o.uuid = u.id
==> Parameters:
<== Total: 5
order{id = 1, ordertime = Thu Jan 01 13:36:51 CST 1970, total = 12.5, uuid = 1, user = user{id = 1, username = aa, password = 1233, birthday = Thu Jan 01 13:37:01 CST 1970}}
order{id = 2, ordertime = Thu Jan 01 13:36:51 CST 1970, total = 12.5, uuid = 3, user = user{id = 3, username = cc, password = 2133, birthday = Thu Jan 01 10:50:11 CST 1970}}
order{id = 3, ordertime = Thu Jan 01 13:38:31 CST 1970, total = 12.5, uuid = 2, user = user{id = 2, username = bb, password = 2133, birthday = Thu Jan 01 13:36:51 CST 1970}}
order{id = 4, ordertime = Thu Jan 01 13:37:01 CST 1970, total = 15.0, uuid = 2, user = user{id = 2, username = bb, password = 2133, birthday = Thu Jan 01 13:36:51 CST 1970}}
order{id = 5, ordertime = Thu Jan 01 13:37:01 CST 1970, total = 15.0, uuid = 1, user = user{id = 1, username = aa, password = 1233, birthday = Thu Jan 01 13:37:01 CST 1970}}
2、一对多查询（结构和上面一样下面只展示代码）：
修改底层Javabean：
订单表：
package org.Emp;
import java.util.Date;
import java.util.List;
public class order {
private Integer id;
private Date ordertime;
private Double total;
private Integer uuid;
public order() {
}
public order(Integer id, Date ordertime, Double total, Integer uuid) {
this.id = id;
this.ordertime = ordertime;
this.total = total;
this.uuid = uuid;
}
/**
* 获取
* @return id
*/
public Integer getId() {
return id;
}
/**
* 设置
* @param id
*/
public void setId(Integer id) {
this.id = id;
}
/**
* 获取
* @return ordertime
*/
public Date getOrdertime() {
return ordertime;
}
/**
* 设置
* @param ordertime
*/
public void setOrdertime(Date ordertime) {
this.ordertime = ordertime;
}
/**
* 获取
* @return total
*/
public Double getTotal() {
return total;
}
/**
* 设置
* @param total
*/
public void setTotal(Double total) {
this.total = total;
}
/**
* 获取
* @return uuid
*/
public Integer getUuid() {
return uuid;
}
/**
* 设置
* @param uuid
*/
public void setUuid(Integer uuid) {
this.uuid = uuid;
}
public String toString() {
return "order{id = " + id + ", ordertime = " + ordertime + ", total = " + total + ", uuid = " + uuid + "}";
}
// private user user;
}
用户表：
package org.Emp;
import java.util.Date;
import java.util.List;
public class user {
private Integer id;
private String username;
private String password;
private Date birthday;
private List<order> order;
public user() {
}
public user(Integer id, String username, String password, Date birthday, List<order> order) {
this.id = id;
this.username = username;
this.password = password;
this.birthday = birthday;
this.order = order;
}
/**
* 获取
* @return id
*/
public Integer getId() {
return id;
}
/**
* 设置
* @param id
*/
public void setId(Integer id) {
this.id = id;
}
/**
* 获取
* @return username
*/
public String getUsername() {
return username;
}
/**
* 设置
* @param username
*/
public void setUsername(String username) {
this.username = username;
}
/**
* 获取
* @return password
*/
public String getPassword() {
return password;
}
/**
* 设置
* @param password
*/
public void setPassword(String password) {
this.password = password;
}
/**
* 获取
* @return birthday
*/
public Date getBirthday() {
return birthday;
}
/**
* 设置
* @param birthday
*/
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
/**
* 获取
* @return order
*/
public List<order> getOrder() {
return order;
}
/**
* 设置
* @param order
*/
public void setOrder(List<order> order) {
this.order = order;
}
public String toString() {
return "user{id = " + id + ", username = " + username + ", password = " + password + ", birthday = " + birthday + ", order = " + order + "}";
}
}
// private List<role> role;
写Mapper映射（核心）：
<?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="org.dao.oneselMapper">
<resultMap id="userMap" type="org.Emp.user">
<id column="uuid" property="id"></id>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<!--集合映射 (Collection)-->
<collection property="order" ofType="org.Emp.order">
<id column="oid" property="id"></id>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
</collection>
</resultMap>
<!--数据库的一对多查询-->
<select id="onefindallduo" resultMap="userMap">
select *,o.id oid from user u,orders o where o.uuid = u.id
</select>
</mapper>
接口：
3、多对多查询：
修改底层Javabean;
role(角色表)：
package org.Emp;
import java.util.List;
public class role {
private Integer id;
private String roleName;
private String roleDesc;
public role() {
}
public role(Integer id, String roleName, String roleDesc) {
this.id = id;
this.roleName = roleName;
this.roleDesc = roleDesc;
}
/**
* 获取
* @return id
*/
public Integer getId() {
return id;
}
/**
* 设置
* @param id
*/
public void setId(Integer id) {
this.id = id;
}
/**
* 获取
* @return roleName
*/
public String getRoleName() {
return roleName;
}
/**
* 设置
* @param roleName
*/
public void setRoleName(String roleName) {
this.roleName = roleName;
}
/**
* 获取
* @return roleDesc
*/
public String getRoleDesc() {
return roleDesc;
}
/**
* 设置
* @param roleDesc
*/
public void setRoleDesc(String roleDesc) {
this.roleDesc = roleDesc;
}
public String toString() {
return "role{id = " + id + ", roleName = " + roleName + ", roleDesc = " + roleDesc + "}";
}
}
user(用户表)：
package org.Emp;
import java.util.Date;
import java.util.List;
public class user {
private Integer id;
private String username;
private String password;
private Date birthday;
private List<role> role;
public user() {
}
public user(Integer id, String username, String password, Date birthday, List<role> role) {
this.id = id;
this.username = username;
this.password = password;
this.birthday = birthday;
this.role = role;
}
/**
* 获取
* @return id
*/
public Integer getId() {
return id;
}
/**
* 设置
* @param id
*/
public void setId(Integer id) {
this.id = id;
}
/**
* 获取
* @return username
*/
public String getUsername() {
return username;
}
/**
* 设置
* @param username
*/
public void setUsername(String username) {
this.username = username;
}
/**
* 获取
* @return password
*/
public String getPassword() {
return password;
}
/**
* 设置
* @param password
*/
public void setPassword(String password) {
this.password = password;
}
/**
* 获取
* @return birthday
*/
public Date getBirthday() {
return birthday;
}
/**
* 设置
* @param birthday
*/
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
/**
* 获取
* @return role
*/
public List<role> getRole() {
return role;
}
/**
* 设置
* @param role
*/
public void setRole(List<role> role) {
this.role = role;
}
public String toString() {
return "user{id = " + id + ", username = " + username + ", password = " + password + ", birthday = " + birthday + ", role = " + role + "}";
}
}
写Mapper映射（核心）：
<?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="org.dao.oneselMapper">
<resultMap id="duoduoMapper" type="org.Emp.user">
<id column="id" property="id"></id>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="role" ofType="org.Emp.role">
<id column="roleid" property="id"></id>
<result column="roleName" property="roleName"></result>
<result column="roleDesc" property="roleDesc"></result>
</collection>
</resultMap>
<!--数据库的多对多查询-->
<select id="duoduoall" resultMap="duoduoMapper">
select * from user u,user_role ur,role r where u.id=ur.userid and r.id=ur.roleid
</select>
</mapper>
接口：
这样我们的两表查询就写完了。
注意：一定要配置核心文件，添加映射文件和数据库和Java互转的方法。
原文链接: https://blog.csdn.net/daibadetianshi/article/details/140698718