使用 scribe oauth facebook 的空指针异常答案

【问题标题】：Null pointer exception using scribe oauth facebook使用 scribe oauth facebook 的空指针异常
【发布时间】：2015-07-09 20:18:06
【问题描述】：

大家好，我正在尝试实施 oauth 2.0 以通过 scribe 获取 facebook 访问令牌并不断获取空指针异常。下面的行不断得到一个空指针异常： String authorizationUrl = oAuthService.getAuthorizaionUrl(Token.Empty())+"&"+STATE+"="+state;

下面是我的完整代码

@Controller
public class HomeController {

private static final String STATE = "state";
private String client_id = "********";
private String app_secret = "********";
private String url = "http://localhost:8080";
private static final Token EMPTY_TOKEN = null;
private OAuthService oAuthService;
private FacebookClient obj; //passing the token to restfb object


public HomeController() {}


public HomeController(OAuthService oAuthService) {
    oAuthService = buildOAuthService(client_id, app_secret);
}

private OAuthService buildOAuthService(String client_id, String app_secret){
    return new ServiceBuilder()
            .provider(FacebookApi.class)
            .apiKey(client_id)
            .apiSecret(app_secret)
            .callback(url + "/auth/facebook/callback")
            .build();
     }
  @RequestMapping(value ="/login", method=RequestMethod.GET)
  public String HomePage()
      {
   //home page and has the link to redirect to /auth/facebook
    return "login";
      }

//start the OAuth2 authorization flow
    @RequestMapping(value="/auth/facebook")
    public RedirectView startAuthentication(HttpSession httpSession) throws OAuthException {
         String state = UUID.randomUUID().toString();
         httpSession.setAttribute(STATE, state);
        //Below is where i'm having a null pointer exception
        String authorizationUrl = oAuthService.getAuthorizationUrl(Token.empty())+"&"+STATE+"="+state;
     return new RedirectView(authorizationUrl);
    }

   @RequestMapping(value="/auth/facebook/callback")
   public RedirectView callback(@RequestParam("code")String code, @RequestParam(STATE)String state, HttpSession httpsession) throws IOException
{
     String stateFromSession = (String)httpsession.getAttribute(STATE);
     if(!state.equals(stateFromSession)) {
        return new RedirectView("/login");
      }
    Token accessToken = getAccessToken(code);
    obj = new DefaultFacebookClient(accessToken.toString(), Version.VERSION_2_2);
    return new RedirectView("/loggedin");
   }
   private Token getAccessToken(String code) {
        Verifier verify = new Verifier(code);
        return oAuthService.getAccessToken(Token.empty(), verify);
    }
}

【问题讨论】：

标签： java facebook spring-mvc oauth

【解决方案1】：

您的私人创建的对象变量“oAuthService”为空。由于我们不知道整个逻辑，我假设这是问题所在：

private OAuthService oAuthService;

public HomeController() {}

public HomeController(OAuthService oAuthService) {
    oAuthService = buildOAuthService(client_id, app_secret);
}

如果将最后一个构造函数更改为：

public HomeController(OAuthService oAuthService) {
        this.oAuthService = buildOAuthService(client_id, app_secret);
    }

或

public HomeController(OAuthService oAuthService) {
        this.oAuthService = oAuthService;
    }

它会起作用的。

编辑：关于使用“this”的好帖子可以在这里找到：http://javapapers.com/core-java/explain-the-java-this-keyword/

【讨论】：