Spring Boot REST API 提供空行

Question

我是 Spring Boot 的新手。我有一个 MYSQL 表“客户”，其数据如下所示： Data in the table 使用 Postman 测试 API 输出时，似乎有几行空的 JSON 输出。

API Output

下面是我的代码：

package com.semika.customer;

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

@Entity
@Table(name="customer") 
public class Customer {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name="first_name")
    private String firstName;

    @Column(name="last_name")
    private String lastName;

    @Column(name="address")
    private String address;

    public Customer() {
       super();

    }

}

客户存储库

package com.semika.customer;

import org.springframework.data.repository.CrudRepository;

public interface CustomerRepository extends CrudRepository<Customer, Long>{

}

客户服务

package com.semika.customer;

public interface CustomerService {
    public Iterable<Customer> findAll(); 
}

CustomerServiceImpl

package com.semika.customer;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class CustomerServiceImpl implements CustomerService{

    @Autowired
    private CustomerRepository customerRepository;

    public Iterable<Customer> findAll() {
        return customerRepository.findAll(); 
    }
}

客户控制器

package com.semika.customer;

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

@RestController
public class CustomerController {
    @Autowired
    private CustomerService  customerService;

    @RequestMapping("/customers") 
    @ResponseBody
    public Iterable<Customer> findAll() {
       Iterable<Customer> customers = customerService.findAll();
       return customers;
    }
}

我不知道我还需要在控制器中修改什么才能看到带有数据的输出。

Answer 1

乍一看，您的代码看起来不错。所以，我复制了你的代码并尝试运行它并得到一个空响应，就像你一样。花了一些时间后，我弄清楚了原因。

Use getter and setter in you customer class and recompile the code.

它会解决你的问题。还要进行以下更改：

1) Annotate CustomerRepository with @Repository
2) use @EnableJpaRepositories("package path") in your application's main class if your repository is not in the same or sub package.
3) use method type or @GetMapping annotation in your controller.

为了您的方便，我在所有修改后编写您的代码：

TestDemoApplication.java

    package testdemo;

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

    @SpringBootApplication
    @EnableJpaRepositories("put repository path here")
    public class TestDemoApplication {

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

CustomerServiceImpl.java

package testdemo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class CustomerServiceImpl implements CustomerService{

    @Autowired
    private CustomerRepository customerRepository;

    public Iterable<Customer> findAll() {
        return customerRepository.findAll(); 
    }
}

CustomerService.java

package testdemo;

public interface CustomerService {
    public Iterable<Customer> findAll(); 
}

CustomerRepository.java

package testdemo;

import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface CustomerRepository extends CrudRepository<Customer, Long>{

}

CustomerController.java

package testdemo;

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

@RestController
public class CustomerController {

    @Autowired
    private CustomerService  customerService;

    @GetMapping(value = "/customers") 
     public Iterable<Customer> findAll() {
       Iterable<Customer> customers = customerService.findAll();
       return customers;
    }
}

Customer.java

package testdemo;

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

@Entity
@Table(name="customer") 
public class Customer {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name="first_name")
    private String firstName;

    @Column(name="last_name")
    private String lastName;

    @Column(name="address")
    private String address;

    public Customer() {
       super();

    }

    public Long getId() {
        return id;
    }

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

    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;
    }

    public String getAddress() {
        return address;
    }

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

此外，CrudRepository 在 findAll() 中返回一个 Iterable。它是返回 List 的 JpaRepository，所以不用担心。

Answer 2

您可能需要遍历数据集并将结果添加到 List 或如 Vishal 所述，更改您的接口和实现以返回 List 而不是 Iterable。

package com.semika.customer;

import java.util.*;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
public class CustomerController {
    @Autowired
    private CustomerService  customerService;

    @RequestMapping("/customers") 
    @ResponseBody
    public Iterable<Customer> findAll() {
        List<Customer> results = new ArrayList<>();
        Iterator<Customer> iter = customerService.findAll().iterator();
        while (iter.hasNext()) results.add(iter.next());
        return results;
    }
}

在以下post、Andy 状态下，

虽然List 保证是Iterable，但Iterable 可能不是List。这意味着如果您将Iterable 转换为List，它可能会在运行时失败。即使它有效，也不能保证它会在未来继续有效，因为它可能会在新版本的 Spring Data JPA 中发生变化而不会破坏接口的约定。

您应该声明自己的返回 List 的查询方法，而不是使用强制转换。

在那篇文章中还指出，您可以使用JpaRepository 而不是CrudRepository，因为JPA 将返回List 而不是Iterable，如here 所述。