mysql寫第一個程式_MyBatis第一個程式

思路

搭建環境 --> 導入MyBatis --> 編寫代碼 --> 測試

代碼示範

環境說明：

JDK 8

MySQL 5.7.19

maven-3.6.0

IDEA

1. 建立資料庫并插入資料

CREATE DATABASE `mybatis`;

USE `mybatis`;

DROP TABLE IF EXISTS `user` (

`id` int(10) AUTO_INCREMENT PRIMARY KEY,

`name` varchar(30) DEFAULT NULL,

`pwd` varchar(30) DEFAULT NULL

) ENGIN=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `user` (`name`,`pwd`) values ("linux","linux123") ("windows","windows123","macos","macos123");

2. 導入MyBatis相關jar包

org.mybatis

mybatis

3.5.4

mysql

mysql-connector-java

8.0.19

3. 編寫配置檔案

/p>

PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-config.dtd">

4. 編寫MyBatis工具類

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();

}

}

//擷取SqlSession連接配接

public static SqlSession getSession() {

return sqlSessionFactory.openSession();

}

}

5. 建立實體類

public class User {

private int id;

private String name;

private String pwd;

//有參構造器

//無參構造器

//set方法

//get方法

//toString重寫

}

上面注釋的部分自己寫，或使用IDEA就能生成，在編輯區快捷鍵Alt + Insert，toString要重寫，不然第8步列印會輸出該對象的引用，格式為包名.類名.@八位字元。

6. 編寫Mapper接口類

import com.geek.pojo.User;

import java.util.List;

public interface UserMapper {

List selectUser();

}

7. 編寫Mapper.xml配置檔案

注意：namespace不要寫錯，否則會報錯

/p>

PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

select * from user

8. 編寫測試類

Junit包測試

public class MyTest {

@Test

public void selectUser() {

SqlSession session = MybatisUtils.getSession();

//方法一:

//List users = session.selectList("com.geek.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();

}

}

9. 運作測試

可能出現的問題

Maven靜态資源過濾問題

src/main/java

***.xml

false

src/main/resources

***.xml

false

第7步Mapper.xml中命名空間寫錯，可能會報類似這樣的錯誤

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException:

### Error updating database. Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for xxdfly.mapping.userMaper.updateUser

### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for xxdfly.mapping.userMaper.updateUser

at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)

at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:154)

at test.MybatisTest.main(MybatisTest.java:37)

Caused by: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for xxdfly.mapping.userMaper.updateUser