java - Spring Boot Autowiring 存储库始终为空

This question already has answers here:

Why is my Spring @Autowired field null?

(18个回答)


4年前关闭。




每次进入服务类时，存储库似乎都不会自动装配，因为它会不断抛出NullPointerException。谁能帮我检查我想念的是什么？

这是我的代码:

DemoApplication.java

package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.orm.jpa.EntityScan;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.stereotype.Controller;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Configuration
@EnableAutoConfiguration
@ComponentScan({"com.example", "com.controller", "com.repositories", "com.service", "com.model"})
@EntityScan(basePackages = {"com.model"})
@EnableJpaRepositories(basePackages = {"com.repositories"})
@EnableTransactionManagement
public class DemoApplication {

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

人.java

package com.model;

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)
    long id;

    String firstName;

    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;
    }
}

PersonRepository.java

package com.repositories;

import com.model.Person;
import org.springframework.data.repository.CrudRepository;

public interface PersonRepository extends CrudRepository<Person, Long> {

}

PersonService.java

package com.service;

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

import java.util.List;


import com.model.Person;
import com.repositories.PersonRepository;


@Service
public class PersonService {

    private PersonRepository pr;

    @Autowired
    public void setPersonRepository(PersonRepository pr) {
        this.pr = pr;
    }

    public List<Person> listAll() {
        return null;

    }

    public Person getByName(String firstName, String lastName) {
        return null;
    }

    public Person saveOrUpdate(Person p) {
        pr.save(p);
        return p;
    }

}

application.properties

spring.datasource.url:jdbc:h2:mem:testdb
spring.datasource.username=sa
spring.datasource.password=
spring.datasource.driverClassName=org.h2.Driver

pom.xml

<?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>

    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.3.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.7</java.version>
    </properties>

    <dependencies>
        <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>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.hibernate.javax.persistence</groupId>
            <artifactId>hibernate-jpa-2.1-api</artifactId>
            <version>1.0.0.Final</version>
        </dependency>

        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>javax.persistence</artifactId>
            <version>2.0.0</version>
            <scope>compile</scope>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>

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

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


</project>

PersonController.java

package com.controller;

import javax.servlet.http.HttpServletRequest;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.ui.ModelMap;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.support.SessionStatus;

import com.model.Person;
import com.service.PersonService;

@Controller
public class PersonController {
    @RequestMapping("/person")
    public String person(Model model) {
        PersonService ps = new PersonService();
        Person p = ps.getByName("John", "Doe");
        model.addAttribute("person", p);
        return "personview";
    }




    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String getHomePage() {
        return "homeview";
    }

    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String getRegFormPage(ModelMap model) {
        model.addAttribute("person", new Person());
        return "addpersonview";
    }

    @RequestMapping(value="/add", method = RequestMethod.POST)
    public String processRegFormPage(ModelMap model,  @ModelAttribute("person") Person p, BindingResult result, SessionStatus status, HttpServletRequest request) throws Exception {
            PersonService ps = new PersonService();
            ps.saveOrUpdate(p);

            model.addAttribute("person", p);
            return "personview";
        }
}

最佳答案

错误是在控制器中手动实例化PersonService，例如PersonService ps = new PersonService()。

为了使Spring能够自动装配任何东西，您需要使用它所管理的bean，因此，与其自动在控制器上创建新的PersonService，不如:

@Autowired
private PersonService personService;