如何使用GWT處理JSONP回調？

Question

我正在使用GWT，我想創建一個JSONP請求，它在返回時調用我的GWT方法。

但是，我無法弄清楚如何指定GWT方法來調用回調。誰能幫忙？這裏是我的示例代碼：

private native void fetchUserData(String accessToken) /*-{ 
    var callback = "com.company.example.FacebookApi::handleUser"; 
    var url = "https://graph.facebook.com/me?access_token="+accessToken+"&callback=" + callback; 

    // use jsonp to call the graph 
    var script = document.createElement('script'); 
    script.src = url; 
    document.body.appendChild(script); 

    }-*/; 

    public void handleUser(Object o) { 
    Window.alert("Received object with class: " + o.getClass().getName()) 
    } 

此代碼是從這個例子移植：Facebook Without SDK。

另外，我剛剛發現有一個GWT JsonpRequestBuilder，我還沒有機會使用，但如果任何人都可以舉一個例子，而不使用任何本機代碼......那就更好了。

謝謝！

Answer 1

想通了，由於在很大程度上這些例子：

Gwt + JSONP

Cross Domain Requests with Gwt, Jsonp

Cross site referenceing in GWT

下面是更新後的代碼，每個註釋（沒有指定的回調，使用Javascript Overlay Type）

private void fetchDataUsingGwt() { 
    String url = "https://graph.facebook.com/me?access_token=" + accessToken; 
    JsonpRequestBuilder requestBuilder = new JsonpRequestBuilder(); 
    requestBuilder.requestObject(url, new AsyncCallback<FbUser>() { 
    @Override 
    public void onFailure(Throwable caught) { 
    Window.alert(caught.getMessage()); 
    } 

    @Override 
    public void onSuccess(FbUser fbUser) { 
     if (fbUser.isError()) { 
     StringBuilder builder = new StringBuilder(); 
     builder.append("Fb error: "); 
     builder.append(fbUser.getError().getMessage() + ", "); 
     builder.append(fbUser.getError().getCode()); 
     String message = builder.toString(); 
     Window.alert(message); 
     return; 
     } 

     StringBuilder builder = new StringBuilder(); 
     builder.append("Fetched user: " + fbUser.getFirstName() + " " + fbUser.getLastName()); 
     builder.append(" from " + fbUser.getHometown().getName()); 
     builder.append(" born on " + fbUser.getBirthday()); 
     builder.append(" with id " + fbUser.getId() + " and email " + fbUser.getEmail()); 
     builder.toString(); 
     String details = builder.toString(); 
     Window.alert("Got: " + details); 
    } 
}); 

}

，並且響應使用JSO像這樣自動換：

public class FbError extends JavaScriptObject { 
    protected FbError() { 
    } 

    public final native String getMessage() /*-{ 
      return this.message; 
    }-*/; 

    public final native String getType() /*-{ 
      return this.type; 
    }-*/; 

    public final native String getCode() /*-{ 
      return this.code; 
    }-*/; 

    public final native String getSubCode() /*-{ 
      return this.error_subcode; 
    }-*/; 

    } 

    public class Hometown extends JavaScriptObject { 
    protected Hometown() { 
    } 

    public final native String getName() /*-{ 
      return this.name; 
    }-*/; 

    public final native String getId() /*-{ 
      return this.id; 
    }-*/; 
    } 

    public class ErrorableJso extends JavaScriptObject { 

    public boolean isError() { 
     return getError() != null; 
    } 

    public final native FbError getError() /*-{ 
      return this.error; 
    }-*/; 
    } 

    public class FbUser extends ErrorableJso { 

    // TODO: Separate call needed to retrieve profile pic 

    protected FbUser() { 
    } 

    public final native String getFirstName() /*-{ 
      return this.first_name; 
    }-*/; 

    public final native String getLastName() /*-{ 
      return this.last_name; 
    }-*/; 

    public final native String getId() /*-{ 
      return this.id; 
    }-*/; 

    public final native String getBirthday() /*-{ 
      return this.birthday; 
    }-*/; 

    public final native String getEmail() /*-{ 
      return this.email; 
    }-*/; 

    public final native Hometown getHometown() /*-{ 
      return this.hometown; 
    }-*/; 
    } 

爲了完整性，這是原始JSON響應JSO包裝。因繼承，使用相同的FbUser對象，如果有任何像這樣的錯誤：

{ 
    "error": { 
     "message": "Error validating access token: Session has expired at unix time 1342044000. The current unix time is 1342050026.", 
     "type": "OAuthException", 
     "code": 190, 
     "error_subcode": 463 
    } 
} 

或者預期的用戶對象：

{ 
    "id": "23232323", 
    "name": "Andrew Cuga", 
    "first_name": "Andrew", 
    "last_name": "Cuga", 
    "link": "http://www.facebook.com/TheAndy", 
    "username": "TheAndy", 
    "birthday": "02/20/2011", 
    "hometown": { 
     "id": "108530542504412", 
     "name": "Newark, Delaware" 
    } // ... etc 
} 

注意error和hometown領域的JSON響應是輕鬆包裝成JavaScriptObjects。