SpringBoot和JPA整合

今天药忘吃喽~ 2022-05-11 06:28 225阅读 0赞

项目结构：

![70][]

pom.xml:

<?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>com.Lucifer.pringboot</groupId>
        <artifactId>springboot-jpa</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <packaging>jar</packaging>
    
        <name>springboot-jpa</name>
        <description>Demo project for Spring Boot</description>
    
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>2.0.5.RELEASE</version>
            <relativePath/> 
        </parent>
    
        <properties>
            <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
            <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
            <java.version>1.8</java.version>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-jpa</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-jdbc</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
    
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
            </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>
                </plugin>
            </plugins>
        </build>
    
    
    </project>

application.yml:

spring:
      datasource:
        url: jdbc:mysql://localhost:3306/test
        username: root
        password: 123456
        driver-class-name: com.mysql.jdbc.Driver
      jpa:
        hibernate:
          ddl-auto: update
          naming:
            physical-strategy: org.springframework.boot.orm.jpa.hibernate.SpringPhysicalNamingStrategy
    
        show-sql: true

开启驼峰命名：
    spring.hibernate.naming.physical-strategy: org.springframework.boot.orm.jpa.hibernate.SpringPhysicalNamingStrategy
    
    如果不开启的话，查询的lastname是null,因为表中字段是last_name，需要开启驼峰命名规则。

![70 1][]

spring.jpa.show-sql: true 打印sql语句。

User实体类：

package com.lucifer.springboot.jpa.entity;
    
    import javax.persistence.*;
    
    /**
     * @author: Lucifer
     * @create: 2018-09-20 16:21
     * @description:
     **/
    
    /*
        使用JPA注解配置映射关系
        @Entity 告诉jpa这是一个实体类（和数据库表映射的类）
        @Table 指定和哪个数据表对应；如果省略name,默认表名是user
     */
    
    @Entity
    @Table(name = "tbl_user")
    public class User {
    
        /**
         * 自增主键id
         */
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Integer id;
    
        @Column(name = "last_name", length = 50)//这是和数据表对应的一个列
        private String lastname;
    
        /**
         * 省略默认列名就是属性名
         */
        @Column
        private String email;
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getLastname() {
            return lastname;
        }
    
        public void setLastname(String lastname) {
            this.lastname = lastname;
        }
    
        public String getEmail() {
            return email;
        }
    
        public void setEmail(String email) {
            this.email = email;
        }
    }

UserRepository接口：

package com.lucifer.springboot.jpa.repository;
    
    import com.lucifer.springboot.jpa.entity.User;
    import org.springframework.data.jpa.repository.JpaRepository;
    
    /**
     * 继承JpaRepository来完成对数据库表的操作
     */
    public interface UserRepository extends JpaRepository<User,Integer> {
    
    
    }

查看JpaRepository接口源码，可以发现里面有很多对于数据库表增删改查操作的接口。

/*
     * Copyright 2008-2016 the original author or authors.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    package org.springframework.data.jpa.repository;
    
    import java.util.List;
    
    import javax.persistence.EntityManager;
    
    import org.springframework.data.domain.Example;
    import org.springframework.data.domain.Sort;
    import org.springframework.data.repository.NoRepositoryBean;
    import org.springframework.data.repository.PagingAndSortingRepository;
    import org.springframework.data.repository.query.QueryByExampleExecutor;
    
    /**
     * JPA specific extension of {@link org.springframework.data.repository.Repository}.
     *
     * @author Oliver Gierke
     * @author Christoph Strobl
     * @author Mark Paluch
     */
    @NoRepositoryBean
    public interface JpaRepository<T, ID> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {
    
    	/*
    	 * (non-Javadoc)
    	 * @see org.springframework.data.repository.CrudRepository#findAll()
    	 */
    	List<T> findAll();
    
    	/*
    	 * (non-Javadoc)
    	 * @see org.springframework.data.repository.PagingAndSortingRepository#findAll(org.springframework.data.domain.Sort)
    	 */
    	List<T> findAll(Sort sort);
    
    	/*
    	 * (non-Javadoc)
    	 * @see org.springframework.data.repository.CrudRepository#findAll(java.lang.Iterable)
    	 */
    	List<T> findAllById(Iterable<ID> ids);
    
    	/*
    	 * (non-Javadoc)
    	 * @see org.springframework.data.repository.CrudRepository#save(java.lang.Iterable)
    	 */
    	<S extends T> List<S> saveAll(Iterable<S> entities);
    
    	/**
    	 * Flushes all pending changes to the database.
    	 */
    	void flush();
    
    	/**
    	 * Saves an entity and flushes changes instantly.
    	 *
    	 * @param entity
    	 * @return the saved entity
    	 */
    	<S extends T> S saveAndFlush(S entity);
    
    	/**
    	 * Deletes the given entities in a batch which means it will create a single {@link Query}. Assume that we will clear
    	 * the {@link javax.persistence.EntityManager} after the call.
    	 *
    	 * @param entities
    	 */
    	void deleteInBatch(Iterable<T> entities);
    
    	/**
    	 * Deletes all entities in a batch call.
    	 */
    	void deleteAllInBatch();
    
    	/**
    	 * Returns a reference to the entity with the given identifier.
    	 *
    	 * @param id must not be {@literal null}.
    	 * @return a reference to the entity with the given identifier.
    	 * @see EntityManager#getReference(Class, Object)
    	 * @throws javax.persistence.EntityNotFoundException if no entity exists for given {@code id}.
    	 */
    	T getOne(ID id);
    
    	/*
    	 * (non-Javadoc)
    	 * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example)
    	 */
    	@Override
    	<S extends T> List<S> findAll(Example<S> example);
    
    	/*
    	 * (non-Javadoc)
    	 * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example, org.springframework.data.domain.Sort)
    	 */
    	@Override
    	<S extends T> List<S> findAll(Example<S> example, Sort sort);
    }

SpringbootJpaApplication启动类：

package com.lucifer.springboot.jpa;
    
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    
    @SpringBootApplication
    public class SpringbootJpaApplication {
    
        public static void main(String[] args) {
            SpringApplication.run(SpringbootJpaApplication.class, args);
        }
    }

UserController：

package com.lucifer.springboot.jpa.controller;
    
    import com.lucifer.springboot.jpa.entity.User;
    import com.lucifer.springboot.jpa.repository.UserRepository;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.RestController;
    
    
    /**
     * @author: Lucifer
     * @create: 2018-09-20 17:10
     * @description:
     **/
    @RestController
    public class UserController {
    
        @Autowired
        UserRepository userRepository;
    
    
        @GetMapping("/insert")
        public User insertuser(User user){
            User save = userRepository.save(user);
            return save;
        }
    
        @GetMapping(value = "/user/{id}")
        public User getuser(@PathVariable("id") Integer id){
            User user = userRepository.findById(id).get();
            return user;
        }
    }

ps:查看源码，findById(ID id)这个方法是Optional<T>接收的。

![70 2][]

而UserController类中的getuser方法是用user来接收的，所以可以直接

User user = userRepository.findById(id);

下图可能更容易理解：

![70 3][]

源码：

![70 4][]

如果数据库表中为空，没有数据，执行查询会报错。

![70 5][]

因此查询之前，有必要做个非空判断的。

最后------》

在浏览器中输入请求，执行对应的sql语句，打印在控制台，此时整合成功！！！！

![70 6][]

[70]: /images/20220511/89e5d6f7c2e74ee1a94e81b481d1b5ff.png
[70 1]: /images/20220511/33f6503648154f46b5fcc7aa2ea23b21.png
[70 2]: /images/20220511/bda721883c3c45e3bcecead354de67fe.png
[70 3]: /images/20220511/793bdd2ba7bb4e538584106d976ffe20.png
[70 4]: /images/20220511/fa0d9275647c4230859fb83f16deee7e.png
[70 5]: /images/20220511/7a4d8a740c2d441f904d4957dae07ae8.png
[70 6]: /images/20220511/9cc57db906244596853277779ceb3edf.png