springboot web使用mybatis访问mysql库

思想：

重点：spring boot项目可以配置mybatis必须的内容。默认配置文件为“main/resources/application.properties”(yml为其另一种写法，感兴趣自己去查)

一切编码跟普通的mybatis相同。

注意：

xml文件最好放在资源文件夹resources下面，以便编译时直接复制。

由此引起需要在springboot项目配置文件下指定mapper文件夹位置，详见操作。

---

操作：

1、官网新建项目：

主要目录结构如下：

 2、编写项目配置文件"application.properties"

# JDBC 驱动
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
# JDBC URL
spring.datasource.url=jdbc:mysql://xxx.xxx.xxx.xxx:xxxx/d1?useSSL=false
# 用户名
spring.datasource.username=root
# 密码
spring.datasource.password=xxxxxxxx
#mapper资源文件
mybatis.mapper-locations=classpath:map/*.xml
#实体文件位置。因mapper文件中都使用了全限定名，故可以没有。
#mybatis.type-aliases-package=hc.entity

前面都好理解。

第10行：编译以后，资源文件夹下的“map文件夹及其内容”会被复制到“target\classes”下面，故需要指定编译后mapper文件的位置。

3、编写实体文件、表操作接口、表操作实现。

实体文件t1.java:

package hc.entity;

public class t1 {
    public String xm;
    public int nl;
}

表操作接口t1Mapper.java:

package hc.data;
import org.apache.ibatis.annotations.Mapper;

import hc.entity.t1;
@Mapper
public interface t1Mapper {
    t1 getByXm(String xm);
}

说明：第五行的Mapper注解必不可少。它除了实现Component注解的容器注册功能，还通知mybatis需要查找实现（xml）

表操作实现t1Mapper.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="hc.data.t1Mapper">
  <select id="getByXm" resultType="hc.entity.t1">
    select * from t1 where xm = #{xm}
  </select>
</mapper>

说明：xml本质上不属于java程序，建议放在资源文件夹下，在编译时自动复制。

4、配置测试文件"C1ApplicationTests.java"

package hc;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import hc.data.t1Mapper;
import hc.entity.t1;

@SpringBootTest(classes=C1Application.class)
class C1ApplicationTests {
    @Autowired
    t1Mapper tm;
    @Test
    void contextLoads() {
        t1 myt1=tm.getByXm("ls");
        System.out.println(myt1.xm);
        System.out.println(myt1.nl);
    }

}

说明：第12行实现t1Mapper对象tm的自动装配， 得益于其接口java文件中的Mapper注解。

5、运行测试

PS C:\Hc\1\Test1> mvn test 
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------------------< hc:Test1 >------------------------------
[INFO] Building C1 0.0.1-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- resources:3.3.1:resources (default-resources) @ Test1 ---
[INFO] Copying 1 resource from src\main\resources to target\classes
[INFO] Copying 1 resource from src\main\resources to target\classes
[INFO] 
[INFO] --- compiler:3.11.0:compile (default-compile) @ Test1 ---
[INFO] Changes detected - recompiling the module! :source
[INFO] Compiling 3 source files with javac [debug release 21] to target\classes
[INFO] 
[INFO] --- resources:3.3.1:testResources (default-testResources) @ Test1 ---
[INFO] skip non existing resourceDirectory C:\Hc\1\Test1\src\test\resources
[INFO]
[INFO] --- compiler:3.11.0:testCompile (default-testCompile) @ Test1 ---
[INFO] Changes detected - recompiling the module! :dependency
[INFO] Compiling 1 source file with javac [debug release 21] to target\test-classes
[INFO] 
[INFO] --- surefire:3.0.0:test (default-test) @ Test1 ---
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running hc.C1ApplicationTests

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v3.1.4)

2023-10-04T23:00:09.707+08:00  INFO 7968 --- [           main] hc.C1ApplicationTests                    : Starting C1ApplicationTests using Java 21 with PID 7968 (started by Morning in C:\Hc\1\Test1)
2023-10-04T23:00:09.710+08:00  INFO 7968 --- [           main] hc.C1ApplicationTests                    : No active profile set, falling back to 1 default profile: "default"   
2023-10-04T23:00:11.314+08:00  INFO 7968 --- [           main] hc.C1ApplicationTests                    : Started C1ApplicationTests in 1.916 seconds (process running for 2.825)
Java HotSpot(TM) 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
WARNING: A Java agent has been loaded dynamically (C:\Users\Morning\.m2\repository\net\bytebuddy\byte-buddy-agent\1.14.8\byte-buddy-agent-1.14.8.jar)
WARNING: If a serviceability tool is in use, please run with -XX:+EnableDynamicAgentLoading to hide this warning
WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
WARNING: Dynamic loading of agents will be disallowed by default in a future release
2023-10-04T23:00:12.181+08:00  INFO 7968 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2023-10-04T23:00:12.448+08:00  INFO 7968 --- [           main] com.zaxxer.hikari.pool.HikariPool        : HikariPool-1 - Added connection com.mysql.cj.jdbc.ConnectionImpl@3de56885
2023-10-04T23:00:12.450+08:00  INFO 7968 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
ls
18
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 3.537 s - in hc.C1ApplicationTests
[INFO] 
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  6.936 s
[INFO] Finished at: 2023-10-04T23:00:12+08:00
[INFO] ------------------------------------------------------------------------

在第51、52行能看到测试的输出结果。

（完）