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;
}
调用getFolderJson()Web服务被成功调用.但结果在收到之前返回.所以我得到了retunr值“initial_value”.
当getFolderJson()函数时如何从响应中返回值？
解决方法
GWT不支持同步Ajax,因此您必须使用异步模式对应用进行编码.
GWT用于执行请求的低级对象是XMLHttpRequest(除了旧版本的IE版本),而GWT总是将async设置为true来调用它的open()方法.所以,同步ajax的唯一方法就是维护你自己修改的XMLHttpRequest.java版本.但是同步的ajax是一个坏主意,甚至jQuery已经不赞成这种可能性.
所以gwt中的正常方法应该是你的方法返回void,并且当响应可用时,你传递一个带有回调的附加参数来执行.
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gwtquery Promises语法,而不是请求构建器一：
Ajax.get("http://localhost/folder?sessionId=foo&path=bar")
.done(new Function(){
public void f() {
String text = arguments(0);
}
});
