将HATEOAS与Spring Boot和MongoTemplate结合使用时不会提取数据

Question

我正在尝试将HATEOAS与Spring boot和MongoTemplate一起使用。当我不使用HATEOAS（即不继承自ResourceSupport）时，它工作正常。但是，当我从实体类扩展ResourceSupport时，我根本无法提取实体列表。它给出了NullPointerException。这是代码。

SpringMongoConfig.java

package com.mindtree.learnmongo.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.config.AbstractMongoConfiguration;
import org.springframework.data.mongodb.core.MongoTemplate;

import com.mongodb.MongoClient;

@Configuration
public class SpringMongoConfig extends AbstractMongoConfiguration {

    @Override
    public MongoClient mongoClient() {
        return new MongoClient();
    }

    @Override
    protected String getDatabaseName() {
        // TODO Auto-generated method stub
        return "studentdb";
    }


    /*
    public MongoDbFactory mongoDbFactory() throws Exception {
        return new SimpleMongoDbFactory(new MongoClient(), "studentdb");
    }*/

    public MongoTemplate mongoTemplate() throws Exception {
        MongoTemplate mongoTemplate = new MongoTemplate(mongoDbFactory());
        return mongoTemplate;
    }


}

控制器类：

HelloController.java

package com.mindtree.learnmongo.controller;

import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.hateoas.mvc.ControllerLinkBuilder;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.AbstractController;

import com.mindtree.learnmongo.model.User;
import com.mindtree.learnmongo.service.UserService;

@RestController
@CrossOrigin
public class HelloController extends AbstractController {

    @Autowired
    private UserService userService;

    @GetMapping(value = "/", produces = {"application/json; charset=utf-8"})
    public List<User> getAllUser(){
        List<User> u = this.userService.getAllUser();
        //System.out.println(this.userService.getAllUser());
        u.forEach(user -> {
            user.add(ControllerLinkBuilder.linkTo(HelloController.class).slash(user.getUserId()).withSelfRel());
            });
        return u;
        //return u;

        //this.userService.getAllUser().forEach(u -> u.add(linkTo(methodOn(HelloController.class).getUserById(u.getUserid())).withSelfRel()));
        //return this.userService.getAllUser();
        /*
        List<User> u = this.userService.getAllUser();

        List<Resource<User>> res = new ArrayList<Resource<User>>();
        */
    }

    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
            throws Exception {
        // TODO Auto-generated method stub
        return null;
    }

}

实体类

package com.mindtree.learnmongo.model;

import java.util.List;

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;
import org.springframework.hateoas.Link;
import org.springframework.hateoas.ResourceSupport;

@Document(collection = "users")
public class User extends ResourceSupport {

    @Id
    private String id;

    String username;
    String password;

    public User() {
        super();
    }

    public User(String username, String password) {
        super();
        this.username = username;
        this.password = password;
    }

    public String getUserId() {
        return id;
    }

    public void setUserId(String id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }



}

服务类别

package com.mindtree.learnmongo.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.stereotype.Service;

import com.mindtree.learnmongo.config.SpringMongoConfig;
import com.mindtree.learnmongo.model.User;

@Service
public class UserService {

    @Autowired
    private SpringMongoConfig springMongoConfig;

    public int haha = 34;
    public List<User> getAllUser() {
        try {
            System.out.print("haha");
            MongoOperations mongoOperation = this.springMongoConfig.mongoTemplate();
            System.out.print("haha");
            List<User> lst = mongoOperation.findAll(User.class);
            System.out.println(lst+" hahaha");
            return lst;
        } catch (Exception e) {
            System.out.println(e+" HAHA EXCEPTION");
            return null;
        }
    }
}

主要的。

package com.mindtree.learnmongo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class LearnmongoApplication {

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

有很多评论。一直在尝试一切。什么都没用。