Question

使用springboot进行演示，遇到异常：搜索了两个原因：手动初始化类;没有在类上设置注释。检查不是这两个问题

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootAngularSample1Application {
public static void main(String[] args) {
    SpringApplication.run(SpringBootAngularSample1Application.class, args);
}
}

控制器用户= userService.saveAll（用户）的异常点; userService为null。

package com.example.demo.geek;

import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    import org.springframework.web.bind.annotation.*;
    import java.util.ArrayList;
    import java.util.List;

/**
 * Created by Damith Ganegoda on 9/3/17.
 */

@CrossOrigin(origins = "http://localhost:4200")
@RestController
@RequestMapping(value = "/users")

public class UserController {


private List<User> users = new ArrayList();

@Autowired
private UserService userService;

UserController() {
    this.users = buildUsers();
}

@RequestMapping(method = RequestMethod.GET)
public List<User> getUsers() {
    return this.users;
}

@RequestMapping(value = "/{id}", method = RequestMethod.GET)
public User getUser(@PathVariable("id") Long id) {
    return this.users.stream().filter(user -> user.getId() == id).findFirst().orElse(null);
}

@RequestMapping(method = RequestMethod.POST)
public User saveUser(@RequestBody User user) {
    Long nextId = 0L;
    if (this.users.size() != 0) {
        User lastUser = this.users.stream().skip(this.users.size() - 1).findFirst().orElse(null);
        nextId = lastUser.getId() + 1;
    }

    user = userService.saveUser(user);
    this.users.add(user);
    return user;

}

@RequestMapping(method = RequestMethod.PUT)
public User updateUser(@RequestBody User user) {
    User modifiedUser = this.users.stream().filter(u -> u.getId() == user.getId()).findFirst().orElse(null);
    modifiedUser.setFirstName(user.getFirstName());
    modifiedUser.setLastName(user.getLastName());
    modifiedUser.setEmail(user.getEmail());
    modifiedUser = userService.saveAndFlush(modifiedUser);
    return modifiedUser;
}

@RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
public boolean deleteUser(@PathVariable Long id) {
    User deleteUser = this.users.stream().filter(user -> user.getId() == id).findFirst().orElse(null);
    if (deleteUser != null) {
        userService.deleteUser(deleteUser);
        this.users.remove(deleteUser);
        return true;
    } else  {
        return false;
    }


}

List<User> buildUsers() {
    List<User> users = new ArrayList<>();

    User user1 = buildUser("John", "Doe", "john@email.com");
    User user2 = buildUser("Jon", "Smith", "smith@email.com");
    User user3 = buildUser("Will", "Craig", "will@email.com");
    User user4 = buildUser("Sam", "Lernorad", "sam@email.com");
    User user5 = buildUser("Ross", "Doe", "ross@email.com");

    users.add(user1);
    users.add(user2);
    users.add(user3);
    users.add(user4);
    users.add(user5);

    users = userService.saveAll(users);
//      userRepo.save(user1);
    return users;

}

User buildUser(String fname, String lname, String email) {
    User user = new User();

    user.setFirstName(fname);
    user.setLastName(lname);
    user.setEmail(email);
    return user;
}

}

第3。带注释的服务，存储库是自动装配的

@Service
public class UserService {

    @Autowired
    UserRepository userRepo;

    public User saveUser(User user) {
        return userRepo.save(user);
    }

    public User saveAndFlush(User user) {
        return userRepo.saveAndFlush(user);
    }
    public List<User> saveAll(List<User> users) {
        return userRepo.saveAll(users);
    }
    public void deleteUser(User user) {
        userRepo.delete(user);
    }
}

4。存储库

@Repository
public interface UserRepository extends JpaRepository<User, String> {
}

错误消息：

    org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userController' defined in file [C:\workstation_bz\workspace\spring-boot-angular-sample-1\target\classes\com\example\demo\geek\UserController.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.demo.geek.UserController]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1232) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
    at o

rg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1131) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:502) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:312) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:310) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868) ~[spring-context-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:752) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:388) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1246) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1234) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
        at com.example.demo.SpringBootAngularSample1Application.main(SpringBootAngularSample1Application.java:12) [classes/:na]
    Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.demo.geek.UserController]: Constructor threw exception; nested exception is java.lang.NullPointerException
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:182) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:87) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1224) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        ... 17 common frames omitted
    Caused by: java.lang.NullPointerException: null
        at com.example.demo.geek.UserController.buildUsers(UserController.java:90) ~[classes/:na]
        at com.example.demo.geek.UserController.<init>(UserController.java:24) ~[classes/:na]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_152]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_152]
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_152]
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_152]
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:170) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
        ... 19 common frames omitted

Answer 1

此代码在您的控制器中存在问题。在UserController对象实例化之前，您正在尝试使用userService对象。

UserController() {
    this.users = buildUsers();
}

而是在控制器中实现InitializingBean，并在afterPropertiesSet（）方法中调用buildUsers（）方法。在实例化对象od UserController类之后调用afterPropertiesSet（）方法 @override

public void afterPropertiesSet() throws Exception {
    // TODO Auto-generated method stub
}

Answer 2

在调用buildUsers（）之前，您应该使用构造函数注入而不是UserService的字段注入来确保它是实例化的：

在UserController中：

private final UserService userService;

UserController(UserService userService) {
    this.userService = userService;
    this.users = buildUsers();
}

这将阻止它在行

处的空指针

users = userService.saveAll(users)

springboot autowired无法初始化类，获取NullPointerException

2 个答案: