在 Java 中使用 Spring RestTemplate 时出现 NullPointedException

Question

我正在使用最新的 Springframework，但在尝试从我的服务器获取 int 时遇到问题。所有代码都是用 Java 编写的。

当我通过浏览器与服务器交互时，一切正常。当通过客户端与服务器交互时，我得到一个NullPointerException。

请记住，我是一名软件初学者。

服务器代码（我都试过了，在使用浏览器时效果很好）：

public class RestController {

    private GameSession gameSession = new GameSession();

    @RequestMapping(value = "registerPlayer")
    public int registerPlayer(@RequestParam("name") String name, @RequestParam("mode") boolean mode) {
        return gameSession.registerPlayer(name, mode);
    }

    @RequestMapping(value = "registerPlayer/{name}/{mode}")
    public int registerPlayer(@PathVariable String name, @PathVariable boolean mode) {
        return gameSession.registerPlayer(name, mode);
    }

}

客户端代码（再次尝试两者，结果相同）：

@Component
public class GameSessionClient implements ISeaBattleGame{

    @Autowired
    private RestOperations restOperations;
    private String url;

    @Override
    public int registerPlayer(String name, boolean singlePlayerMode) {
        url = "http://localhost:8080/" + "registerPlayer?name=" + name + "&mode=" + (singlePlayerMode ? 1 : 0);
        return restOperations.getForObject(url, int.class);
    }

    @Override
    public int registerPlayer(String name, boolean singlePlayerMode) {
        url = "http://localhost:8080/" + "registerPlayer/" + name + "/" + (singlePlayerMode ? 1 : 0);
        return restOperations.getForObject(url, int.class);
    }
}

RestConfig 代码：

@Configuration
public class RestConfig {

    @Bean
    public RestOperations createRestTemplate(final ClientHttpRequestFactory clientHttpRequestFactory){
        return new RestTemplate(clientHttpRequestFactory);
    }

    @Bean
    public ClientHttpRequestFactory clientHttpRequestFactory(@Value("${connect.timeout}") final int connectTimeout, @Value("${read.timeout}") final int readTimeout){
        HttpComponentsClientHttpRequestFactory httpComponentsClientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
        httpComponentsClientHttpRequestFactory.setReadTimeout(readTimeout);
        httpComponentsClientHttpRequestFactory.setConnectTimeout(connectTimeout);
        return httpComponentsClientHttpRequestFactory;
    }
}

应用代码：

@SpringBootApplication
public class App implements CommandLineRunner {

    private static final Logger logger = LoggerFactory.getLogger(Application.class);

    @Autowired
    private GameSessionClient gameSessionClient;

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

    @Override
    public void run(String... args) throws Exception {
        int playerNr = gameSessionClient.registerPlayer("test", true);
        logger.info("Response: {}", playerNr);
    }
}

return restOperations.getForObject(url, int.class); 的结果是 java.lang.NullPointerException

url：http://localhost:8080/registerPlayer/test/1 或 http://localhost:8080/registerPlayer?name=test&mode=1 在使用我的浏览器时都会导致 1

任何帮助将不胜感激，因为我对此感到很困惑。

Answer 1

将您的代码更新到下面..将删除您获得的 NullPointer 异常：

@Bean
    public RestOperations restOperations(final ClientHttpRequestFactory clientHttpRequestFactory){
        return new RestTemplate(clientHttpRequestFactory);
    }

并这样做，而不是“Application.class”：

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