springboot系类代码：springboot-data-jpa_spring data jpa怎么注入entityinformation

JPA 的目标之一是制定一个可以由很多供应商实现的API，并且开发人员可以编码来实现该API，而不是使用私有供应商特有的API。因此开发人员只需使用供应商特有的API来获得JPA规范没有解决但应用程序中需要的功能。尽可能地使用JPA API，但是当需要供应商公开但是规范中没有提供的功能时，则使用供应商特有的API。

package com.programb;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

import com.programb.common.SimpleJpaRepositoryImpl;

@EnableJpaRepositories(value = "com.programb.repository", repositoryBaseClass = SimpleJpaRepositoryImpl.class)
@SpringBootApplication
public class JpaApplication {

    public static void main(String[] args) {
        SpringApplication.run(JpaApplication.class, args);
    }
}

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package com.programb.common;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.repository.support.JpaEntityInformation;
import org.springframework.data.jpa.repository.support.SimpleJpaRepository;
import org.springframework.util.StringUtils;
import javax.persistence.EntityManager;
import javax.transaction.Transactional;
import java.beans.PropertyDescriptor;
import java.util.HashSet;
import java.util.Optional;
import java.util.Set;
import java.util.UUID;


public class SimpleJpaRepositoryImpl<T, ID> extends SimpleJpaRepository<T, ID> {

    private final JpaEntityInformation<T, ?> entityInformation;
    private final EntityManager em;

    @Autowired
    public SimpleJpaRepositoryImpl(JpaEntityInformation<T, ?> entityInformation, EntityManager entityManager) {
        super(entityInformation, entityManager);
        this.entityInformation = entityInformation;
        this.em = entityManager;
    }


    @Override
    @Transactional
    public <S extends T> S save(S entity) {
        //获取ID
        ID entityId = (ID) entityInformation.getId(entity);
        Optional<T> optionalT;
        if (StringUtils.isEmpty(entityId)) {
            String uuid = UUID.randomUUID().toString();
            //防止UUID重复
            if (findById((ID) uuid).isPresent()) {
                uuid = UUID.randomUUID().toString();
            }
            //若ID为空 则设置为UUID
            new BeanWrapperImpl(entity).setPropertyValue(entityInformation.getIdAttribute().getName(), uuid);
            //标记为新增数据
            optionalT = Optional.empty();
        } else {
            //若ID非空 则查询最新数据
            optionalT = findById(entityId);
        }
        //获取空属性并处理成null
        String[] nullProperties = getNullProperties(entity);
        //若根据ID查询结果为空
        if (!optionalT.isPresent()) {
            em.persist(entity);//新增
            return entity;
        } else {
            //1.获取最新对象
            T target = optionalT.get();
            //2.将非空属性覆盖到最新对象
            BeanUtils.copyProperties(entity, target, nullProperties);
            //3.更新非空属性
            em.merge(target);
            return entity;
        }

    }


    private static String[] getNullProperties(Object src) {
        //1.获取Bean
        BeanWrapper srcBean = new BeanWrapperImpl(src);
        //2.获取Bean的属性描述
        PropertyDescriptor[] pds = srcBean.getPropertyDescriptors();
        //3.获取Bean的空属性
        Set<String> properties = new HashSet<>();
        for (PropertyDescriptor propertyDescriptor : pds) {
            String propertyName = propertyDescriptor.getName();
            Object propertyValue = srcBean.getPropertyValue(propertyName);
            if (StringUtils.isEmpty(propertyValue)) {
                srcBean.setPropertyValue(propertyName, null);
                properties.add(propertyName);
            }
        }
        return properties.toArray(new String[0]);
    }

}

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package com.programb.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.programb.entity.User;
import com.programb.repository.UserRepository;

import java.util.List;

@RestController
public class UserController {

    @Autowired
    private UserRepository userRepository;

    @RequestMapping("/")
    public List<User> get() {

        userRepository.save(new User("1", "", null));

        return userRepository.findAll();
    }
}

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package com.programb.entity;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import org.hibernate.annotations.GenericGenerator;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "T_USER")
@JsonIgnoreProperties({"handler","hibernateLazyInitializer"})
public class User {

    @Id
    @GenericGenerator(name = "programb",strategy = "uuid")
    @GeneratedValue(generator = "programb")
    private String userId;
    private String username;
    private String password;

    public User() {

    }

    public User(String userId, String username, String password) {
        this.userId = userId;
        this.username = username;
        this.password = password;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "userId='" + userId + '\'' +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

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package com.programb.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import com.programb.entity.User;


public interface UserRepository extends JpaRepository<User, String> {


}

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spring:
  datasource:
    url: jdbc:mysql://localhost:3306/socks?useSSL=false
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver


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drop table if exists t_user;
create table t_user (
  user_id  varchar(50),
  username varchar(50),
  password varchar(50)
);

insert into t_user values ('1', 'admin', 'admin');
insert into t_user values ('2', 'programb', '123456');
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<?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.programb</groupId>
    <artifactId>springboot-data-jpa</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>springboot-data-jpa</name>
    <description>jpa</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.1.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-web</artifactId>
        </dependency>

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

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </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>

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