如何在Spring控制器中使用ID搜索（主键）？

Question

我试图通过传递键从JpaRepository的getOne中按主键搜索

我有一个模型（客户），其中定义了客户的详细信息。我有一个接口服务（CustomerService）及其实现（CustomerServiceImpl，它实现CustomerService）。我还有一个接口存储库（CustomerRepository），它扩展了JpaRepository。现在在我的控制器中，我将id传递给函数（findCustomerById），并使用JpaRepository的getOne从客户存储库中获取具有该id的客户

Customer=customerRepository。getOne（id）；

我不断收到一个错误（java.lang.NullPointerException:null）。我的代码似乎没问题。会是什么问题？Customer.java

package com.javadevjournal.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();

    }

    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;
    }
}

客户存储。java：

package com.javadevjournal.customer;

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

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

}

CustomerController。java：

package com.javadevjournal.customer;

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

import org.springframework.http.HttpHeaders;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.util.UriComponentsBuilder;
import com.javadevjournal.customer.CustomerService;

import javax.validation.Valid;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;

@RestController
public class CustomerController {

    @Autowired
    private CustomerService  customerService;
    private CustomerRepository customerRepository;

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

    // Get a Single Customer
    @GetMapping(path = "/getCustomer/{id}")
    public Customer findCustomerById(@PathVariable("id") Long id) {
        System.out.println("Am going on here...");
        System.out.println("id=="+id);
        System.out.println("fetching customers.."+id);
        Customer customer=customerRepository.getOne(id);
        System.out.println(customer);
        return customer;
    }

    // Create a new Customer
    @PostMapping("/customers")
    public Customer createCustomer(@Valid @RequestBody Customer customer) {
        return customerRepository.save(customer);
    }


}

我希望根据邮递员传递的ID获得特定客户(http://localhost:8080/getCustomer/1)但邮递员给了我以下错误消息：

Answer 1

正如上面提到的，您错过了@Autowyah注释。另请注意，推荐的摄取方式是抛出类构造函数或setter

@RestController
public class CustomerController {
    private final CustomerService  customerService;
    private final CustomerRepository customerRepository;

    @Autowire
    public CustomerController(CustomerService  customerService, CustomerRepository customerRepository) {
        customerService = customerService;
        customerRepository = customerRepository;
    }

    // the rest of your code
}

很酷的事情，这种DI的工作原理也没有@Autow的注释）

Answer 2

您已放弃在customerRepository上添加Autowired

@Autowired
private CustomerService  customerService;
@Autowired
private CustomerRepository customerRepository;