Gwt请求构建器 - 如何返回响应字符串

Question

我需要实现一个调用Web服务并返回响应的函数.

我试过了

public String getFolderJson(String path) {  
           String result="initial_value";
           StringBuilder param = new StringBuilder();  
           param.append("?sessionId=").append(getSessionId());  
           param.append("&path=").append(path);  
           RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, "https://localhost/folder" + param);  
                   try {  
                        builder.sendRequest(null, new RequestCallback() {  
                        @Override  
                        public void onResponseReceived(Request request,
                                Response response) {  
                              result = response.getText();
                              System.out.println(response.getText());  
                                            //I need to return "result"   
                        }  
                        @Override  
                        public void onError(Request request, Throwable exception) {}  
                          });  
                    return result; //the result get returned before the response is recieved.So i am getting the return value "initial_value".
                   }      
                   catch (RequestException e) {}  
        return null;
    }

在调用 getFolderJson()Web服务时成功调用.但是result在收到respnse之前返回.所以我得到了retunr值"initial_value".
如何在getFolderJson()功能时从响应中返回值？

Answer 1

GWT不支持同步Ajax,因此您必须使用异步模式对应用程序进行编码.

GWT用于执行请求的低级对象是XMLHttpRequest(旧的IE版本除外),并且GWT始终将其open()async设置为true 的方法调用.因此,拥有同步ajax的唯一方法是维护自己的修改版本XMLHttpRequest.java.但同步ajax是一个坏主意,甚至jQuery已经弃用了这种可能性.

因此,gwt中的常规方法应该是您的方法返回void,并且在响应可用时传递带回调的附加参数.

public void getFolderJson(String path, Callback<String, String> callback) {  
    RequestBuilder builder = new RequestBuilder(...);
    try {
      builder.sendRequest(null, new RequestCallback() {  
        @Override  
        public void onResponseReceived(Request request, Response response) {
          callback.onSuccess(response.getText());  
        }  
        @Override  
        public void onError(Request request, Throwable exception) {}
          callback.onFailure(exception.getMessage());  
        });
    } catch (RequestException e) {
        callback.onFailure(exception.getMessage());  
    }  
}

我宁愿使用gwtquery Promises语法而不是请求构建器:

  Ajax.get("http://localhost/folder?sessionId=foo&path=bar")
    .done(new Function(){
      public void f() {
        String text = arguments(0);
      }
    });