我的第一个mybatis程序（含纠错）

我的第一个mybatis程序

编写一个mybatis程序的主要流程：

• 搭建需要的环境

• 导入相关jar包

• 编写代码

• 运行测试

搭建环境

使用MySQL数据库

创建一个表名为mybatis，写入几行数据，具体代码如下：

CREATE DATABASE `mybatis`;      //新建数据库
​
USE `mybatis`;
CREATE TABLE `user`(            //创建表
    `id` INT(20) NOT NULL,
    `name` VARCHAR(30) DEFAULT NULL,
    `pwd` VARCHAR(30) DEFAULT NULL,
    PRIMARY KEY(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8;
​
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES        //写入数据
(1,'hayden','9918'),
(2,'wong','8899'),
(3,'jane','123456')

创建项目

• 新建一个普通的maven项目

• 删除该项目下的src目录，使其成为一个父工程（方便之后进行在父工程下创建子工程）

• 在pom.xml中导入依赖（MySQL驱动、mybatis、junit）

   
      <dependencies>
          
          <dependency>
              <groupId>mysqlgroupId>
              <artifactId>mysql-connector-javaartifactId>
              <version>5.1.46version>
          dependency>
          
          <dependency>
              <groupId>org.mybatisgroupId>
              <artifactId>mybatisartifactId>
              <version>3.5.5version>
          dependency>
          
          <dependency>
              <groupId>junitgroupId>
              <artifactId>junitartifactId>
              <version>4.12version>
              <scope>testscope>
          dependency>
      dependencies>

创建一个模块

• 在之前的父工程下创建一个模块（本子模块就可以使用原来父工程的pom.xml中导入的jar包）

• 配置核心配置：在新建的子工程目录下的src/main/resourses目录下新建文件：mybatis-config.xml，并写入下列核心配置文件

  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="${driver}"/>
                  <property name="url" value="${url}"/>
                  <property name="username" value="${username}"/>
                  <property name="password" value="${password}"/>
              dataSource>
          environment>
      environments>
       
      <mappers>
          <mapper resource="com.wong.dao.UserMapper.xml"/>
      mappers>
  configuration>

  将其中的value值修改为我们需要的：

  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/mybatis?useSSL=false&userUnicode=true&characterEncoding=UTF-8"/>
                  <property name="username" value="root"/>
                  <property name="password" value="123456"/>
              dataSource>
          environment>
      environments>
      
      <mappers>
          <mapper resource="com.wong.dao.UserMapper.xml"/>
      mappers>
  configuration>

• 编写mybatis工具类（在java目录下创建包Utils，创建类MybatisUtils，使用sql语言时就需要用到这个工具类）

  package com.wong.utils;
  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 java.io.IOException;
  import java.io.InputStream;
  public class MybatisUtils {
      private static SqlSessionFactory sqlSessionFactory;
      static {
          try {
              String resource = "mybatis-config.xml";
              InputStream inputStream = Resources.getResourceAsStream(resource);
              sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
      //获取SqlSession连接
      public static SqlSession getSession(){
          return sqlSessionFactory.openSession();
      }
  }

编写代码

• 数据库相关实体类

  package com.wong.pojo;
  ​
  public class User {
      private int id;
      private String name;
      private String pwd;
  ​
      public User() {
      }
  ​
      public User(int id, String name, String pwd) {
          this.id = id;
          this.name = name;
          this.pwd = pwd;
      }
  ​
      public int getId() {
          return id;
      }
  ​
      public void setId(int id) {
          this.id = id;
      }
  ​
      public String getName() {
          return name;
      }
  ​
      public void setName(String name) {
          this.name = name;
      }
  ​
      public String getPwd() {
          return pwd;
      }
  ​
      public void setPwd(String pwd) {
          this.pwd = pwd;
      }
  ​
      @Override
      public String toString() {
          return "User{" +
                  "id=" + id +
                  ", name='" + name + '\'' +
                  ", pwd='" + pwd + '\'' +
                  '}';
      }
  }

• Dao接口

  package com.wong.dao;
  ​
  import com.wong.pojo.User;
  ​
  import java.util.List;
  ​
  public interface UserMapper {
      List selectUser();
  }

• 接口实现

  
  DOCTYPE mapper
          PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
          "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  
  
  ​
      
      select * from user
    
  ​
  

  测试

  package com.wong.dao;
  import com.wong.pojo.User;
  import com.wong.utils.MybatisUtils;
  import org.apache.ibatis.session.SqlSession;
  import org.junit.Test;
  import java.util.List;
  public class MyTest {
      @Test
      public void selectUser() {
          SqlSession session = MybatisUtils.getSession();
          //方法一:
          //List users = session.selectList("com.wong.mapper.UserMapper.selectUser");
          //方法二:
          UserMapper mapper = session.getMapper(UserMapper.class);
          List users = mapper.selectUser();
          for (User user: users){
              System.out.println(user);
          }
          session.close();
      }
  }

  得到结果：

  User{id=1, name='hayden', pwd='9918'}
  User{id=2, name='wong', pwd='8899'}
  User{id=3, name='jane', pwd='123456'}
  ​
  Process finished with exit code 0

代码文件位置图

常见报错

• org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. 异常解决

  完整的url的value如下: jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=utf8

• org.apache.ibatis.binding.BindingException: Invalid bound statement (not found):

  核心配置文件中缺少：

  或者名称错误！

• java.lang.ExceptionInInitializerError //初始化异常

  在pom.xml中添加以下代码：

  
  <build>
      <resources>
          <resource>
              <directory>src/main/javadirectory>
              <includes>
                  <include>**/*.propertiesinclude>
                  <include>**/*.xmlinclude>
              includes>
              <filtering>falsefiltering>
          resource>
          <resource>
              <directory>src/main/resourcesdirectory>
              <includes>
                  <include>**/*.propertiesinclude>
                  <include>**/*.xmlinclude>
              includes>
              <filtering>falsefiltering>
          resource>
      resources>
  build>