Question

我正在尝试从JpaRepository的getOne中通过主键来搜索主键

我有一个模型（客户），在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（实现CustomerService的CustomerServiceImpl）。我还有一个接口存储库（扩展JpaRepository的CustomerRepository。现在在我的控制器中，我将一个ID传递给一个函数（findCustomerById），并使用JpaRepository的getOne

从客户存储库中获取具有该ID的客户。

Customer customer = customerRepository.getOne（id）;

我一直遇到错误500 (java.lang.NullPointerException: null。我的代码似乎还可以。可能是什么问题？ 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;
    }
}

CustomerRepository.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);
    }


}

我期望从ID中获取特定的客户是从邮递员（http://localhost:8080/getCustomer/1）传递过来的，但邮递员却给我以下错误消息：

此应用程序没有针对/ error的显式映射，因此您看到了作为后备。星期二6月25日11:58:47 EAT 2019 意外错误（类型=内部服务器错误，状态= 500）。没有讯息在以下位置提供了java.lang.NullPointerException com.javadevjournal.customer.CustomerController.findCustomerById（CustomerController.java:43）在sun.reflect.NativeMethodAccessorImpl.invoke0（本机方法）处 sun.reflect.NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:62）在 sun.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43）在java.lang.reflect.Method.invoke（Method.java:498）在 org.springframework.web.method.support.InvocableHandlerMethod.doInvoke（InvocableHandlerMethod.java:190）在 org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest（InvocableHandlerMethod.java:138）在 org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle（ServletInvocableHandlerMethod.java:104）在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod（RequestMappingHandlerAdapter.java:892）在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal（RequestMappingHandlerAdapter.java:797）在 org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle（AbstractHandlerMethodAdapter.java:87）在 org.springframework.web.servlet.DispatcherServlet.doDispatch（DispatcherServlet.java:1039）在 org.springframework.web.servlet.DispatcherServlet.doService（DispatcherServlet.java:942）在 org.springframework.web.servlet.FrameworkServlet.processRequest（FrameworkServlet.java:1005）在 org.springframework.web.servlet.FrameworkServlet.doGet（FrameworkServlet.java:897）在javax.servlet.http.HttpServlet.service（HttpServlet.java:634）在 org.springframework.web.servlet.FrameworkServlet.service（FrameworkServlet.java:882）在javax.servlet.http.HttpServlet.service（HttpServlet.java:741）处 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:231）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.apache.tomcat.websocket.server.WsFilter.doFilter（WsFilter.java:53）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.springframework.web.filter.RequestContextFilter.doFilterInternal（RequestContextFilter.java:99）在 org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:109）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.springframework.web.filter.FormContentFilter.doFilterInternal（FormContentFilter.java:92）在 org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:109）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal（HiddenHttpMethodFilter.java:93）在 org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:109）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal（CharacterEncodingFilter.java:200）在 org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:109）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.apache.catalina.core.StandardWrapperValve.invoke（StandardWrapperValve.java:202）在 org.apache.catalina.core.StandardContextValve.invoke（StandardContextValve.java:96）在 org.apache.catalina.authenticator.AuthenticatorBase.invoke（AuthenticatorBase.java:490）在 org.apache.catalina.core.StandardHostValve.invoke（StandardHostValve.java:139）在 org.apache.catalina.valves.ErrorReportValve.invoke（ErrorReportValve.java:92）在 org.apache.catalina.core.StandardEngineValve.invoke（StandardEngineValve.java:74）在 org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:343）在 org.apache.coyote.http11.Http11Processor.service（Http11Processor.java:408）在 org.apache.coyote.AbstractProcessorLight.process（AbstractProcessorLight.java:66）在 org.apache.coyote.AbstractProtocol $ ConnectionHandler.process（AbstractProtocol.java:853）在 org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun（NioEndpoint.java:1587）在 org.apache.tomcat.util.net.SocketProcessorBase.run（SocketProcessorBase.java:49）在 java.util.concurrent.ThreadPoolExecutor.runWorker（ThreadPoolExecutor.java:1142）在 java.util.concurrent.ThreadPoolExecutor $ Worker.run（ThreadPoolExecutor.java:617）在 org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run（TaskThread.java:61）在java.lang.Thread.run（Thread.java:745）

Answer 1

您已禁止在@Autowired上添加customerRepository

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

Answer 2

如上所述，您错过了@Autowired注释。还要注意，建议的摄取方式是抛出类构造函数或setters

@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
}

在没有@Autowired批注的情况下，这种DI也可以使用的很酷的东西）

如何在Spring Controller中使用ID（主键）搜索？

2 个答案: