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Spring社区的一个顶级工程,主要用于简化数据(关系型&非关系型)访问,如果我们使用Spring Data来开发程序的话,那么可以省去很多低级别的数据访问操作,如编写数据查询语句、DAO类等,我们仅需要编写一些抽象接口并定义相关操作即可,Spring会在运行期间的时候创建代理实例来实现我们接口中定义的操作。

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Spring Data拥有很多子项目,除了Spring Data Jpa外,还有如下子项目。

Spring Data Commons

Spring Data MongoDB

Spring Data Redis

Spring Data Solr

Spring Data Gemfire

Spring Data REST

Spring Data Neo4j

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Spring Data Jpa是Spring Data的一个子项目,主要用于简化数据访问层的实现,使用Spring Data Jpa可以轻松实现增删改查、分页、排序等。

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1、添加POM.XML文件#

如下所示:

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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.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring-data-jpa-example</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.4.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.7</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-test</artifactId>
            <scope>test</scope>
        </dependency>

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

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>
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其中,spring-boot-starter-parent会加载Spring Boot应用所需的所有默认配置;

spring-boot-starter-data-jpa会下载所有Spring Data Jpa所需的依赖;

添加spring-boot-starter-web是因为我们的工程是一个Web应用;

另外我们的数据库是mysql,所以还需要mysql-connector-java依赖;

由于使用了缓存,所以再添加一个spring-boot-starter-cache依赖;

2、编写实体类User#

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package com.example.domain;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.NamedQuery;

@Entity
@NamedQuery(name = "User.findByName", query = "select name,address from User u where u.name=?1")
public class User implements Serializable
{
    private static final long serialVersionUID = 1L;
    @Id
    long id;
    @Column(name = "name")
    String name;
    @Column(name = "address")
    String address;

    public long getId()
    {
        return id;
    }

    public void setId(long id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public String getAddress()
    {
        return address;
    }

    public void setAddress(String address)
    {
        this.address = address;
    }

}
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其它没啥好说的,注意下这里的@NamedQuery注解,大致意思就是让我们在Repository接口中定义的findByName方法不使用默认的查询实现,取而代之的是使用这条自定义的查询语句去查询,如果这里没有标注的话,会使用默认实现的。

3、编写Repository接口#

这里将编写两个Repository接口,仅仅用于示例,实际中可以合并成一个:

UserJpaRepository 
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package com.example.repository;

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

import com.example.domain.User;


public interface UserJpaRepository extends JpaRepository<User,Long> {

}
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这里的UserJpaRepository接口实现了JpaRepository接口;

实际上JpaRepository实现了PagingAndSortingRepository接口,PagingAndSortingRepository接口实现了CrudRepository接口,CrudRepository接口实现了Repository接口;

简单说明下:

Repository接口是一个标识接口,里面是空的;

CrudRepository接口定义了增删改查方法;

PagingAndSortingRepository接口用于分页和排序;

由于JpaRepository接口继承了以上所有接口,所以拥有它们声明的所有方法;

另外注意下,以findAll方法为例,JpaRepository接口返回的是List, PagingAndSortingRepository和CrudRepository返回的是迭代器;

UserRepository 
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package com.example.repository;

import java.util.List;

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.Repository;
import org.springframework.data.repository.query.Param;

import com.example.domain.User;

public interface UserRepository extends Repository<User, Long>
{

    List<User> findByNameAndAddress(String name, String address);

    @Query(value = "from User u where u.name=:name")
    List<User> findByName1(@Param("name") String name);

    @Query(value = "select * from #{#entityName} u where u.name=?1", nativeQuery = true)
    List<User> findByName2(String name);

    List<User> findByName(String name);
}
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这里的UserRepository接口主要定义了一些查询方法;

比如这里的findByNameAndAddressfindByName方法,我们是不需要额外定义其它查询语句就可以直接执行的,Spring Data Jpa会根据实体类的属性名字以及方法名自动实现该方法;PS:由于我们在实体类中声明了@NamedQuery注解,实际上findByName方法会使用@NamedQuery注解标注的查询语句去查询;

另外这里的findByName1方法使用了HQL语句查询;

findByName2方法使用了原始的sql语句查询;

4、编写Service#

service接口:

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package com.example.service;

import java.util.List;

import com.example.domain.User;

public interface IUserService
{
    public List<User> findAll();

    public void saveUser(User book);
   
    public User findOne(long id);

    public void delete(long id);

    public List<User> findByName(String name);

}
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接口实现类:

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package com.example.service.impl;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import com.example.domain.User;
import com.example.repository.UserRepository;
import com.example.repository.UserJpaRepository;
import com.example.service.IUserService;

@Service
@Transactional
public class UserServiceImpl implements IUserService
{
    @Autowired
    private UserJpaRepository userJpaRepository;
    @Autowired
    private UserRepository userRepository;

    public List<User> findAll()
    {
        return userJpaRepository.findAll();
    }

    public List<User> findByName(String name)
    {
        List<User> userList1 = userRepository.findByName1(name);
        List<User> userList2 = userRepository.findByName2(name);
        List<User> userList3 = userRepository.findByNameAndAddress(name, "3");
        System.out.println("userList1:" + userList1);
        System.out.println("userList2:" + userList2);
        System.out.println("userList3:" + userList3);
        return userRepository.findByName(name);
    }

    public void saveUser(User book)
    {
        userJpaRepository.save(book);
    }

    @Cacheable("users")
    public User findOne(long id)
    {
        System.out.println("Cached Pages");
        return userJpaRepository.findOne(id);
    }

    public void delete(long id)
    {
        userJpaRepository.delete(id);
    }
}
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这个没啥好说的,调用Repository接口接口的方法即可。

5、编写Controller#

Controller也没啥好说的,调用Service即可,注意下这里的Controller使用@RestController注解来标注,另外URL路径命名按照RESTful风格来命名;

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package com.example.web;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.example.domain.User;
import com.example.service.IUserService;

@RestController
@RequestMapping(value = "/users")
public class UserController
{
    @Autowired
    private IUserService userService;

    @RequestMapping(value = "/add/{id}/{name}/{address}")
    public User addUser(@PathVariable int id, @PathVariable String name,
        @PathVariable String address)
    {
        User user = new User();
        user.setId(id);
        user.setName(name);
        user.setAddress(address);
        userService.saveUser(user);
        return user;
    }

    @RequestMapping(value = "/delete/{id}")
    public void deleteBook(@PathVariable int id)
    {
        userService.delete(id);
    }

    @RequestMapping(value = "/")
    public List<User> getBooks()
    {
        return userService.findAll();
    }

    @RequestMapping(value = "/{id}")
    public User getUser(@PathVariable int id)
    {
        User user = userService.findOne(id);
        return user;
    }

    @RequestMapping(value = "/search/name/{name}")
    public List<User> getBookByName(@PathVariable String name)
    {
        List<User> users = userService.findByName(name);
        return users;
    }

}
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6、配置datasource#

在application.properties文件中添加如下配置:

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spring.jpa.show-sql = true
logging.level.org.springframework.data=DEBUG
spring.jpa.hibernate.ddl-auto=


spring.datasource.url=jdbc:mysql://localhost:3306/demo
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
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如果你使用STS IDE的话,这些属性配置都会自动提示的,省的去查找。

想查看spring.datasource的配置,可以参考这个类:DataSourceProperties.java

7、编写启动类#

比较简单,注意下该类所属的包级别要大于或等于其它类,以保证其它类的注解可以被扫描到。

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package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;

@SpringBootApplication
@EnableCaching
public class SpringDataJpaExampleApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringDataJpaExampleApplication.class, args);
    }
}
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启动main方法,或打成jar包运行;

浏览器输入以下URL,测试即可:

http://localhost:8080/users/

http://localhost:8080/users/add/100/110/111

http://localhost:8080/users/delete/100

http://localhost:8080/users/2

http://localhost:8080/users/search/name/2

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