springboot-JPA

Spring Boot Jpa 介绍

首先了解 Jpa 是什么？

Jpa (Java Persistence API) 是 Sun 官方提出的 Java 持久化规范。它为 Java 开发人员提供了一种对象/关联映射工具来管理 Java 应用中的关系数据。它的出现主要是为了简化现有的持久化开发工作和整合 ORM 技术，结束现在 Hibernate，TopLink，JDO 等 ORM 框架各自为营的局面。

值得注意的是，Jpa是在充分吸收了现有 Hibernate，TopLink，JDO 等 ORM 框架的基础上发展而来的，具有易于使用，伸缩性强等优点。从目前的开发社区的反应上看，Jpa 受到了极大的支持和赞扬，其中就包括了 Spring 与 EJB3. 0的开发团队。

注意:Jpa 是一套规范，不是一套产品，那么像 Hibernate,TopLink,JDO 他们是一套产品，如果说这些产品实现了这个 Jpa 规范，那么我们就可以叫他们为 Jpa 的实现产品。

spring的jpa是一个非常不错的持久层框架，可以理解为就是对Hibrenate进行了封装，比起Mybatis优点在于不用关注sql语句的编写

1.项目搭建

2.具体实现

（1）配置文件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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <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-web</artifactId>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>sqljdbc4</artifactId>
            <version>4.2</version>
        </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>

（2）配置文件application.properties

spring.datasource.driverClassName=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url=jdbc:sqlserver://localhost:1433;DatabaseName=Text
spring.datasource.username=sa
spring.datasource.password=123
spring.jpa.database = sql_server
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.SQLServerDialect

spring.jpa.hibernate.ddl-auto=update


(3)实体类

package com.example.demo;

import com.sun.xml.internal.bind.v2.model.core.ID;

import javax.persistence.*;

@Entity
@Table(name="userinfos") //表名
public class Userinfo {
    @Id//主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    public int ID;

    public String UserName;

    public String Pwd;

    public String Age;

    public Userinfo() {}
    public Userinfo(int id,String userName,String pwd,String age) {
        this.ID=id;
        this.UserName=userName;
        this.Pwd=pwd;
        this.Age=age;
    }

    public int getID() {
        return ID;
    }

    public void setID(int id) {
        this.ID = id;
    }

    public String getUserName() {
        return UserName;
    }

    public void setUserName(String userName) {
        UserName = userName;
    }

    public String getPwd() {
        return Pwd;
    }

    public void setPwd(String pwd) {
        Pwd = pwd;
    }



    public String getAge() {
        return Age;
    }

    public void setAge(String age) {
        Age = age;
    }

(4)  Respository层

package com.example.demo;

import org.springframework.data.jpa.repository.JpaRepository;

import java.util.List;

interface UserinfoRepository extends  JpaRepository<Userinfo,Integer>
{


    List<Userinfo> findAll();

  //  Userinfo findByUserName (String user_name);

}

（5）Controller

package com.example.demo;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;
import java.util.List;

@Controller
@RestController
public class UserController {

    @Resource
    private UserinfoRepository userRepository;



    @RequestMapping("/user")
    public CommonResult User()
    {
        CommonResult result = new CommonResult();
        try {
            System.out.println("UserName");
             List<Userinfo> users= userRepository.findAll();
            result.setData(users);
            return result;
        } catch (Exception e) {
            e.printStackTrace();
            result.setState(500);
            result.setMsg("失败");
            return result;
        }



    }
}

（6）Result 返回类

package com.example.demo;

import java.util.List;

public class CommonResult {
    private Integer state;
    private String msg;
    private Object data;

    public CommonResult() {
        this.state=200;
        this.msg="成功";
    }

    public CommonResult(Integer state, String msg) {
        this.state = state;
        this.msg = msg;
    }

    public CommonResult(Integer state, String msg, Object data) {
        this.state = state;
        this.msg = msg;
        this.data = data;
    }

    public Integer getState() {
        return state;
    }

    public void setState(Integer state) {
        this.state = state;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public Object getData() {
        return data;
    }

    public void setData(Object data) {
        this.data = data;
    }
}

（7）结果

{"state":200,"msg":"成功","data":[{"ID":1,"UserName":"李明","Pwd":"123456","Age":"20","id":1,"userName":"李明","age":"20","pwd":"123456"}]}