SpringBoot使用JPA实现增删查改

运行环境

SpringBoot2.3.0
JDK1.8
IDEA2020.1.2
MySQL5.7

依赖及应用程序配置

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</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>
    <exclusions>
        <exclusion>
            <groupId>org.junit.vintage</groupId>
            <artifactId>junit-vintage-engine</artifactId>
        </exclusion>
    </exclusions>
</dependency>

升级到SpringBoot2.2，spring-boot-starter-test默认使用JUnit 5作为单元测试框架，写单元测试时注解@RunWith(Spring.class)升级为@ExtendWith(SpringExtension.class)
升级到SpringBoot2.3，hibernate-validator从spring-boot-starter-web移除，需要单独引入
升级到SpringBoot2.3，MySQL驱动由com.mysql.jdbc.Driver变更为com.mysql.cj.jdbc.Driver;同时，数据源url需要添加serverTimezone=UTC&useSSL=false参数
升级到SpringBoot2.x，默认不自动注入HiddenHttpMethodFilter ，需要设置spring.mvc.hiddenmethod.filter.enabled=true开启PUT、DELETE方法支持

应用程序配置如下：

spring.application.name=springbootjpa
management.endpoints.jmx.exposure.include=*
management.endpoints.web.exposure.include=*
management.endpoint.health.show-details=always
# 应用服务 WEB 访问端口
server.port=8080
# Actuator Web 访问端口
management.server.port=8081

# mysql setting
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/springbootjpa?serverTimezone=UTC&useSSL=false
spring.datasource.username=username
spring.datasource.password=password

# JPA setting
spring.jpa.properties.hibernate.hbm2ddl.auto=update
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.show-sql=true

# thymeleaf setting
spring.thymeleaf.cache=false

# delete、put方法支持
spring.mvc.hiddenmethod.filter.enabled=true

定义实体

使用@Entity标记实体类

import lombok.Data;

import javax.persistence.*;
import javax.validation.constraints.NotEmpty;
import java.io.Serializable;

@Entity
@Data
public class Article extends BaseEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true)
    @NotEmpty(message = "标题不能为空")
    private String title;

    @Column(nullable = false)
    private String body;
}

为了自动添加创建日期、修改日期、创建人及修改人，我们把创建、修改信息放到父类中由实体类继承，并开启SpringBoot的自动审计功能，将创建/修改信息自动注入

1、定义实体类的父类,@CreatedDate、@LastModifiedDate、@CreatedBy、@LastModifiedBy标注相应字段

import org.hibernate.annotations.Columns;
import org.springframework.data.annotation.CreatedBy;
import org.springframework.data.annotation.CreatedDate;
import org.springframework.data.annotation.LastModifiedBy;
import org.springframework.data.annotation.LastModifiedDate;
import org.springframework.data.jpa.domain.support.AuditingEntityListener;

import javax.persistence.Column;
import javax.persistence.EntityListeners;
import javax.persistence.MappedSuperclass;

@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
public class BaseEntity {
    @CreatedDate
    private Long createTime;

    @LastModifiedDate
    private Long updateTime;
    
    @Column(name = "create_by")
    @CreatedBy
    private String createBy;

    @Column(name = "lastmodified_by")
    @LastModifiedBy
    private String lastmodifiedBy;
    
    public Long getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Long createTime) {
        this.createTime = createTime;
    }

    public Long getUpdateTime() {
        return updateTime;
    }

    public void setUpdateTime(Long updateTime) {
        this.updateTime = updateTime;
    }
    
    public String getCreateBy() {
        return createBy;
    }

    public void setCreateBy(String createBy) {
        this.createBy = createBy;
    }

    public String getLastmodifiedBy() {
        return lastmodifiedBy;
    }

    public void setLastmodifiedBy(String lastmodifiedBy) {
        this.lastmodifiedBy = lastmodifiedBy;
    }
}

@MappedSuperclass注解：

作用于实体类的父类上，父类不生成对应的数据库表
标注@MappedSuperclass的类不能再标注@Entity或@Table注解，也无需实现序列化接口
每个子类（实体类）对应一张数据库表，数据库表包含子类属性和父类属性
标注@MappedSuperclass的类可以直接标注@EntityListeners实体监听器

@EntityListeners(AuditingEntityListener.class)注解：

作用范围仅在标注@MappedSuperclass类的所有继承类中，并且实体监听器可以被其子类继承或重载
开启JPA的审计功能，需要在SpringBoot的入口类标注@EnableJpaAuditing

创建日期、修改日期有默认方法注入值，但创建人和修改人注入则需要手动实现AuditorAware接口:

@Configuration
public class BaseEntityAuditor implements AuditorAware<String> {
    @Override
    public Optional<String> getCurrentAuditor() {
        return "";
    }
}

DAO层实现

JPA支持通过约定方法名进行数据库查询、修改：

import org.springframework.data.jpa.repository.JpaRepository;
import springbootjpa.entity.Article;

public interface ArticleRepository extends JpaRepository<Article, Long> {
    Article findById(long id);
}

通过约定方法名查询，只需实现JpaRepository接口声明查询方法而不需要具体实现

此外，可以在方法上标注@Query实现JPQL或原生SQL查询

JpaRepository<T, ID>,T表示要操作的实体对象，ID表示主键。该接口继承了分页排序接口PadingAndSortRepository,通过构建Pageable实现分页查询：

@Autowired
private ArticleRepository articleRepository;

@RequestMapping("")
public ModelAndView articlelist(@RequestParam(value = "start", defaultValue = "0") Integer start, @RequestParam(value = "limit", defaultValue = "5") Integer limit) {
        start = start < 0 ? 0 : start;
        Sort sort = Sort.by(Sort.Direction.DESC, "id");
        Pageable pageable = PageRequest.of(start, limit, sort);
        Page<Article> page = articleRepository.findAll(pageable);
        ModelAndView modelAndView = new ModelAndView("article/list");
        modelAndView.addObject("page", page);
        return modelAndView;
}

如果根据某一字段排序，可以用Sort.by方法构建Sort对象；如果根据多个字段排序，首先构建Sort.Order数组List<Sort.Order>,然后再传入Sort.by方法构建Sort对象。

PageRequest.of方法生成Pageable对象

Contrller控制器

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.ModelAndView;
import springbootjpa.entity.Article;
import springbootjpa.repository.ArticleRepository;

@Controller
@RequestMapping("/article")
public class ArticleController {
    @Autowired
    private ArticleRepository articleRepository;

    @RequestMapping("")
    public ModelAndView articlelist(@RequestParam(value = "start", defaultValue = "0") Integer start,
                                    @RequestParam(value = "limit", defaultValue = "5") Integer limit) {
        start = start < 0 ? 0 : start;
        Sort sort = Sort.by(Sort.Direction.DESC, "id");
        Pageable pageable = PageRequest.of(start, limit, sort);
        Page<Article> page = articleRepository.findAll(pageable);
        ModelAndView modelAndView = new ModelAndView("article/list");
        modelAndView.addObject("page", page);
        return modelAndView;
    }

    @RequestMapping("/add")
    public String addArticle() {
        return "article/add";
    }

    @PostMapping("")
    public String saveArticle(Article article) {
        articleRepository.save(article);
        return "redirect:/article";
    }

    @GetMapping("/{id}")
    public ModelAndView getArticle(@PathVariable("id") Integer id) {
        Article article = articleRepository.findById(id);
        ModelAndView modelAndView = new ModelAndView("article/show");
        modelAndView.addObject("article", article);
        return modelAndView;
    }

    @DeleteMapping("/{id}")
    public String deleteArticle(@PathVariable("id") long id) {
        System.out.println("put 方法");
        articleRepository.deleteById(id);
        return "redirect:/article";
    }

    @GetMapping("edit/{id}")
    public ModelAndView editArticle(@PathVariable("id") Integer id) {
        Article article = articleRepository.findById(id);
        ModelAndView modelAndView = new ModelAndView("article/edit");
        modelAndView.addObject("article", article);
        return modelAndView;
    }

    @PutMapping("/{id}")
    public String editArticleSave(Article article, long id) {
        System.out.println("put 方法");
        article.setId(id);
        articleRepository.save(article);
        return "redirect:/article";
    }
}

因为<form>表单只能发送GET或POST请求，spring3引入一个监听器HiddenHttpMethodFilter 来将POST请求转换为PUT或POST请求。

SpringBoot2.x开始默认不自动注入HiddenHttpMethodFilter ，需要设置spring.mvc.hiddenmethod.filter.enabled=true开启PUT、DELETE方法支持

配置完后，前端页面需要在表单中加入隐藏域，表明实际请求方法：

<!-- DELETE 请求 -->
<form id="deletePost" method="POST" action="">
    <input type="hidden" name="_method" value="delete">
</form>


<!-- PUT 请求 -->
<form id="putPost" method="POST" action="">
    <input type="hidden" name="_method" value="put">
</form>

其他

th:value和th:field区别：

th:value解析成html，表现为：value="${th:value}"
th:field解析成html，表现为：name="${th:name}" value="${th:value}"

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原文地址：https://www.cnblogs.com/weixia-blog/p/13618603.html