基于SpringBoot3和JDK17，集成H2数据库和jpa

学会用H2数据库，为了快速写出需要处理数据关系的demo。

工程配置

完整demo：https://download.csdn.net/download/weixin_43820556/89385337

pom.xml文件

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>3.2.6</version><relativePath/></parent><groupId>com.donny.demo</groupId><artifactId>h2</artifactId><version>0.0.1-SNAPSHOT</version><name>h2</name><description>Demo project for Spring Boot</description><properties><java.version>17</java.version></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency><dependency><groupId>com.h2database</groupId><artifactId>h2</artifactId><scope>runtime</scope></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-configuration-processor</artifactId><optional>true</optional></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId><configuration><excludes><exclude><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId></exclude></excludes></configuration></plugin></plugins></build></project>

application.properties文件

spring.application.name=h2
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=update
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.datasource.driver-class-name=org.h2.Driver
# 内存模式
#spring.datasource.url=jdbc:h2:mem:test
# 文件持久化模式
spring.datasource.url=jdbc:h2:./db/testdb;AUTO_SERVER=TRUE;
spring.datasource.username=sa
spring.datasource.password=sa
#spring.sql.init.schema-locations=classpath:db/schema.sql
spring.h2.console.path=/h2
spring.h2.console.enabled=true
logging.config=classpath:logback-spring.xml
management.endpoints.web.exposure.include=loggers

练习H2数据库的操作

h2数据库的建表

/*学生*/
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student`
(`id`   INTEGER auto_increment primary key,`name` varchar(50) not null
);/*老师,一个老师可以交好几个班级*/
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher`
(`id`      INTEGER auto_increment primary key,`name`    varchar(50) not null,`subject` varchar(50) not null
);/*班级，一个学生只能在一个班级，一个班级有多名老师和学生*/
DROP TABLE IF EXISTS `grade`;
CREATE TABLE `grade`
(`id`         INTEGER auto_increment primary key,`student_id` INTEGER,`teacher_id` INTEGER,`name`       varchar(50)
);-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student`
VALUES (0, '张三');
INSERT INTO `student`
VALUES (1, '少杰');
INSERT INTO `student`
VALUES (10, '赵子龙');
-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `teacher`
VALUES (0, '张老师', '语文');
INSERT INTO `teacher`
VALUES (1, '王老师', '数学');
INSERT INTO `teacher`
VALUES (2, '陈老师', '英语');
-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `grade`
VALUES (1, 0, 0, '1班');
INSERT INTO `grade`
VALUES (2, 1, 2, '2班');
INSERT INTO `grade`
VALUES (3, 10, 1, 'Z班');

自增主键控制

如果单独插入了数据，则不会与JPA的数据插入时主键相关联，例如，在建表的同时，写入了id为1的数据，则JPA在新增的时候，也会不会新增id为2的数据，还是新增id为1的数据，此时即报错。本人并未解决这种问题，而是将插入数据的操作，全部交由JPA来做，是实现主键自增的统一，如果有网友可以解决此问题，可以留言。

通过JPA来操作数据库

多对多关系，建议拆解成多个1对多的关系，进行表设计。
通过注解控制外键关系

@OneToOne：双向关系，实体键的关系是一对一，此注解用在单端上
@ManyToOne：双向关系，实体键的关系是多对一，此注解用在单端上

练习动态调整日志

引入依赖

        <dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency>

打开管理api（application.properties）

management.endpoints.web.exposure.include=loggers

查看类的目前的日志级别

GET请求：http://127.0.0.1:8080/actuator/loggers/com.donny.demo.h2.controller.LogController

结果

{"effectiveLevel":"DEBUG"}

修改类的日志级别

POST请求：

http://127.0.0.1:8080/actuator/loggers/com.donny.demo.h2.controller.LogController 请求体 {"configuredLevel":"info"}

重新查询

{"configuredLevel":"ERROR","effectiveLevel":"ERROR"}

结果会是在LogController中增加一个配置项。若要取消configuredLevel，只要将请求体改为 {"configuredLevel":null}

测试类

java">package com.donny.demo.h2.controller;import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;/*** @author 1792998761@qq.com* @version 1.0* @since 2024年06月01日 上午11:56*/
@RestController
@RequestMapping("/log")
@Slf4j
public class LogController {@GetMapping("/logger")public String loggerLevel() {log.trace("logger level is trace");log.info("logger level is info");log.debug("logger level is debug");log.warn("logger level is warn");log.error("logger level is error");return "success";}
}

开启日志级别为debug时，输出的是[2024-06-01 15:24:25,180][http-nio-8080-exec-5][ERROR][com.donny.demo.h2.controller.LogController:23] logger level is error。说明生效了。