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如何将异常处理程序添加到GWT的服务器端?

exception-handling gwt java

corsiKa · 技术社区 · 6 年前

我想包装来自GWT服务器的所有传出异常(只有服务器,客户端上没有):

public class AuthServiceImpl extends RemoteServiceServlet implements AuthService {
    public String loginAttemt(String username, String password) {
        AwesomeUser user = AwesomeUserDao.forUsername(username);
        if(BCrpyt.checkpw(user.getPasshash(), password)) {
            String code = magicallyGenerateErrorCode();
            logger.error("Invalid login attempt - error code"  + code);
            throw new AwesomeException("password", "Invalid username or password", code);
        }
    }
}

@RemoteServiceRelativePath("auth")
public interface AuthService extends RemoteService {
    String loginAttempt(String username, String password) throws AwesomeException;
}

public interface AuthServiceAsync {
    void loginAttempt(String username, String password, AsyncCallback<String> callback) throws AwesomeException;
}

现在,这是可行的。在我的客户方面,我只是这样做( getField(String)

public void onFailure(Throwable caught) {
    if(caught instanceof AwesomeException) {
        AwesomeException a = (AwesomeException)caught;
        getField(a.getfield()).setErrorText(a.getText());
        getField("error-code").setText(a.getCode());
    }
}

是的,这和预期的一样。但想象一下 user 是 null -你们中的一些人可能会读到“哦,天哪,如果用户名不存在,他可能有一个NPE在那里”,你是绝对正确的。当然,我会防御性地编写这样的代码。然而,我不会抓住所有这些情况。我想在某处添加一个异常处理程序,它捕获所有这些异常并将它们封装在 AwesomeException

(错误代码实际上是一个请求ID—每个请求都有一个ID,所有日志消息在打印时都使用该ID—因此,如果他们报告错误代码,我们可以很容易地看到包含该请求的所有日志消息并排除错误。)

2 回复 | 直到 6 年前

fgb 6 年前

而不是服务扩展 RemoteServiceServlet ,您可以创建自己的servlet并委托给 远程服务Servlet 比如:

public class GwtServiceServlet extends HttpServlet {
    public void doPost(final HttpServletRequest request, final HttpServletResponse response) throws ServletException {
        Object delegate = ...;

        RemoteServiceServlet remoteServiceServlet = new RemoteServiceServlet(delegate);
        remoteServiceServlet.init(getServletConfig());
        remoteServiceServlet.doPost(request, response);
    }
}

在哪里? delegate

Tobika 6 年前

RemoteServiceServlet 并执行异常处理,例如 processCall(RPCRequest rpcRequest) 或 doUnexpectedFailure(Throwable e) .

例如。:

此方法仅对不属于该部分的异常或错误调用服务方法的签名,或 SecurityExceptions、SerializationExceptions或

意味着任何NPE等都可以映射到这里的自定义异常。

  protected void doUnexpectedFailure(Throwable e) {
    try {
      getThreadLocalResponse().reset();
    } catch (IllegalStateException ex) {
      /*
       * If we can't reset the request, the only way to signal that something
       * has gone wrong is to throw an exception from here. It should be the
       * case that we call the user's implementation code before emitting data
       * into the response, so the only time that gets tripped is if the object
       * serialization code blows up.
       */
      throw new RuntimeException("Unable to report failure", e);
    }
    ServletContext servletContext = getServletContext();

    String code = magicallyGenerateErrorCode();
    AwesomeException awesomeException = new AwesomeException("error", "Unexpected Error. Pls contact support", code);

    RPCServletUtils.writeResponseForUnexpectedFailure(servletContext,
        getThreadLocalResponse(), awesomeException);
  }