Spring Data JPA 教程系列

使用 JPA 訪問數據

建立項目

打開IDEA -> Create New Project

建立目錄

建立實體

package com.example.demo.entity;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Customer {

    @Id
    @GeneratedValue
    private Long id;
    private String firstName;
    private String lastName;

    protected Customer() {
    }

    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return "Customer{" +
                "id=" + id +
                ", firstName=" + firstName +
                ", lastName=" + lastName +
                '}';
    }
}

建立 repository

建立與實體對應的Repository

package com.example.demo.repository;

import com.example.demo.entity.Customer;
import org.springframework.data.repository.CrudRepository;

import java.util.List;

public interface CustomerRepository extends CrudRepository<Customer, Long> {

    List<Customer> findByLastName(String lastName);

}

經過繼承CrudRepository繼承幾種增刪改查方法，也能夠經過方法名支定義其餘查詢方法。

添加啓動加載類 CommandLineRunner 測試

package com.example.demo;

import com.example.demo.entity.Customer;
import com.example.demo.repository.CustomerRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class SpringDataJpaDemoApplication {

    public static final Logger log = LoggerFactory.getLogger(SpringDataJpaDemoApplication.class);

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

    @Bean
    public CommandLineRunner demo(CustomerRepository repository) {
        return (args -> {

            repository.save(new Customer("Jack", "Bauer"));
            repository.save(new Customer("Chloe", "Brian"));
            repository.save(new Customer("Kim", "Bauer"));
            repository.save(new Customer("David", "Palmer"));
            repository.save(new Customer("Michelle", "Dessler"));

            log.info("Customer found with save() finish");

            log.info("Customer found with findAll()");
            log.info("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
            for (Customer customer : repository.findAll()) {
                log.info(customer.toString());
            }
            log.info("");

            repository.findById(1L).ifPresent(customer -> {
                log.info("Customer found with findById()");
                log.info("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
                log.info(customer.toString());
                log.info("");
            });

            log.info("Customer found with findByLastName('findByLastName')");
            log.info("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
            repository.findByLastName("Bauer").forEach(bauer -> {
                log.info(bauer.toString());
            });
            log.info("");

        });
    }


}

---

運行程序，經過 log 查看效果

使用 REST 訪問 JPA 數據

pom.xml 添加依賴

<?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">
    
    <dependencies>
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>
        
    </dependencies>


</project>

建立實體

package com.example.demo.entity;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Person {
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    
    private String firstName;
    private String lastName;
    
    
    public String getFirstName() {
        return firstName;
    }
    
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    
    public String getLastName() {
        return lastName;
    }
    
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

建立 repository

package com.example.demo.repository;

import com.example.demo.entity.Person;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.data.rest.core.annotation.RepositoryRestResource;

import java.util.List;

@RepositoryRestResource
public interface PersonRepository extends PagingAndSortingRepository<Person, Long> {
    
    List<Person> findPersonByLastName(@Param("name") String name);
    
}

此repository是一個接口，容許您執行涉及Person對象的各類操做。它經過繼承Spring Data Commons中定義的PagingAndSortingRepository接口來獲取這些操做

在運行時，Spring Data REST將自動建立此接口的實現。而後它將使用@RepositoryRestResource註解指導Spring MVC建立RESTful端點/persons。

測試程序

首先看到頂層服務

curl http://localhost:8080/
{
  "_links" : {
    "customers" : {
      "href" : "http://localhost:8080/customers"
    },
    "persons" : {
      "href" : "http://localhost:8080/persons{?page,size,sort}",
      "templated" : true
    },
    "profile" : {
      "href" : "http://localhost:8080/profile"
    }
  }
}

Spring Data REST使用 HAL格式進行JSON輸出。它很是靈活，能夠方便地提供與所服務數據相鄰的連接。

curl http://localhost:8080/persons
{
  "_embedded" : {
    "persons" : [ ]
  },
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/persons{?page,size,sort}",
      "templated" : true
    },
    "profile" : {
      "href" : "http://localhost:8080/profile/persons"
    },
    "search" : {
      "href" : "http://localhost:8080/persons/search"
    }
  },
  "page" : {
    "size" : 20,
    "totalElements" : 0,
    "totalPages" : 0,
    "number" : 0
  }
}

能夠看到customers的也跟着顯示出來了，咱們能夠經過註釋隱藏，固然也能夠全局隱藏：

設置存儲庫檢測策略

Spring Data REST使用RepositoryDetectionStrategy來肯定是否將存儲庫導出爲REST資源。的RepositoryDiscoveryStrategies列舉包括如下值：

Name	Description
DEFAULT	默認，ANNOTATION + VISIBILITY
ALL	公開全部Repository
ANNOTATION	公開@RepositoryRestResource和@RestResource註解的Repository，除非exported設置爲false
VISIBILITY	暴露全部public修飾的Repository

建立配置類

package com.example.demo.config;

import org.springframework.data.rest.core.config.RepositoryRestConfiguration;
import org.springframework.data.rest.core.mapping.RepositoryDetectionStrategy;
import org.springframework.data.rest.webmvc.config.RepositoryRestConfigurer;
import org.springframework.stereotype.Component;

@Component
public class RestConfigurer implements RepositoryRestConfigurer {

    @Override
    public void configureRepositoryRestConfiguration(RepositoryRestConfiguration config) {
        config.setRepositoryDetectionStrategy(RepositoryDetectionStrategy.RepositoryDetectionStrategies.ANNOTATED);
    }

}

測試

curl http://localhost:8080/
{
  "_links" : {
    "persons" : {
      "href" : "http://localhost:8080/persons{?page,size,sort}",
      "templated" : true
    },
    "profile" : {
      "href" : "http://localhost:8080/profile"
    }
  }
}

分頁和排序

分頁

Pageable 是一個由 Spring 定義的接口，它擁有一個實現 PageRequest。讓咱們看看如何建立一個 PageRequest。

Pageable pageable = PageRequest.of(0, 10);
Page<Employee> page = repository.findAll(pageable);

// 也能夠簡單一點

Page<Employee> page = repository.findAll(PageRequest.of(0, 10));

表示請求第一頁10個數據。

若是咱們要訪問下一頁，咱們能夠每次增長頁碼。

PageRequest.of(1, 10);
PageRequest.of(2, 10);
PageRequest.of(3, 10);
...

排序

Spring Data JPA 提供一個Sort對象提供排序機制。讓咱們看一下排序的方式。

repository.findAll(Sort.by("fistName"));

repository.findAll(Sort.by("fistName").ascending().and(Sort.by("lastName").descending());

同時排序和分頁

Pageable pageable = PageRequest.of(0, 20, Sort.by("firstName"));

Pageable pageable = PageRequest.of(0, 20, Sort.by("fistName").ascending().and(Sort.by("lastName").descending());

按示例對象查詢

QueryByExampleExecutor

構建複雜查詢

SpringData JPA 爲了實現 "Domain Driven Design" 中的規範概念，提供了一些列的 Specification 接口，其中最經常使用的即是 ：JpaSpecificationExecutor。

使用 SpringData JPA 構建複雜查詢（join操做，彙集操做等等）都是依賴於 JpaSpecificationExecutor 構建的 Specification 。