5

我正在玩这个从 twitter 获取数据的 Google Web 工具包/GSON 示例。

一切都编译得很好，但是当我作为 Web 应用程序调试时，一切都加载得很好，但是当我单击“搜索”按钮时，出现以下错误：

严重：javax.servlet.ServletContext 日志：调度传入的 RPC 调用 com.google.gwt.user.server.rpc.UnexpectedException 时出现异常：服务方法'public abstract java.util.List com.google.gwt.twittersearch.client.TwitterService .searchTweets(java.lang.String) throws java.io.IOException,java.lang.IllegalArgumentException' throws an unexpected exception: java.lang.RuntimeException: Unable to invoke no-args constructor for class com.google.gwt.twittersearch。 server.TwitterServiceImpl$SearchResponse。向 Gson 注册此类型的 InstanceCreator 可能会解决此问题。在 com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:385) 在 com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:588) 在 com.google .gwt.user.server.rpc.RemoteServiceServlet.processCall（RemoteServiceServlet.java：org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755) 的 HttpConnection$RequestHandler.content(HttpConnection.java:938) org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218) org.mortbay .jetty.HttpConnection.handle(HttpConnection.java:404) 在 org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409) 在 org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582 ) 原因：java.lang.RuntimeException：无法为类 com.google.gwt.twittersearch.server.TwitterServiceImpl$SearchResponse 调用无参数构造函数。向 Gson 注册此类型的 InstanceCreator 可能会解决此问题。在 com.google.gson.internal.ConstructorConstructor$8.construct(ConstructorConstructor.java:167) 在 com.google.gson.internal.bind。

这是 TwitterServiceImpl 代码：

package com.google.gwt.twittersearch.server;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.List;

import com.google.gwt.twittersearch.client.Tweet;
import com.google.gwt.twittersearch.client.TwitterService;
import com.google.gson.Gson;
import com.google.gwt.user.server.rpc.RemoteServiceServlet;

@SuppressWarnings("serial") 
public class TwitterServiceImpl extends RemoteServiceServlet implements
        TwitterService {

    @Override
    public List<Tweet> searchTweets(String query) throws IllegalArgumentException, IOException {
          query = query.trim();
          if (query.isEmpty()) {
            throw new IllegalArgumentException("No search query specified.");
          }

          // see: https://dev.twitter.com/docs/api/1/get/search
          String q = URLEncoder.encode(query, "UTF-8");
          URL url = new URL("http://search.twitter.com/search.json?q=" + q);
          HttpURLConnection connection = (HttpURLConnection) url.openConnection();
          InputStream response = null;
          try {
            response = connection.getInputStream();
            return parseSearchResponse(response);
          } finally {
            if (response != null) {
              response.close();
            }
          }
    }

    @Override
    public String getPrivacyPolicy() throws IOException {
        // see: https://dev.twitter.com/docs/api/1/get/legal/privacy
        URL url = new URL("https://api.twitter.com/1/legal/privacy.json");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        InputStream response = null;
        try {
            response = connection.getInputStream();
            return parsePolicyResponse(response);
        } finally {
            if (response != null) {
                response.close();
            }
        }
    }

    /**
     * Parses the privacy policy response returned from the Twitter API.
     * @param response the response
     * @return the privacy policy
     * @throws IOException if there was a problem reading the response
     */
    private String parsePolicyResponse(InputStream response) throws IOException {
        Reader reader = new InputStreamReader(response);
        PrivacyPolicyResponse privacyPolicyResponse = new Gson().fromJson(reader, PrivacyPolicyResponse.class);
        return privacyPolicyResponse.privacy;
    }

    /**
     * Parses the search response returned from the Twitter API.
     * @param response the response
     * @return the search results
     * @throws IOException if there was a problem reading the response
     */

    private List<Tweet> parseSearchResponse(InputStream response) throws IOException {
          Reader reader = new InputStreamReader(response);
          SearchResponse searchResponse = new Gson().fromJson(reader, SearchResponse.class);
          return searchResponse.results;
        }

    private class PrivacyPolicyResponse {
    public String privacy;
    }


    private class SearchResponse {
      public List<Tweet> results;
    }

}

这是入口点代码：

    package com.google.gwt.twittersearch.client;

import java.util.List;
import com.google.gwt.safehtml.shared.SafeHtmlBuilder;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.HTML;
import com.google.gwt.user.client.ui.HorizontalPanel;
import com.google.gwt.user.client.ui.Image;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.Panel;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;
import com.google.gwt.user.client.ui.VerticalPanel;

/**
 * Entry point classes define <code>onModuleLoad()</code>.
 */
public class TwitterSearch implements EntryPoint {
  private Button privacyPolicyButton;
  private Button searchButton;
  private TextBox searchQueryTextBox;
  private Panel resultsPanel;
  private Label errorLabel;
  private Image loadingImage;
  private final TwitterServiceAsync service = GWT.create(TwitterService.class);

/**
 * This is the entry point method.
 */
public void onModuleLoad() {
    createWidgets();
    layoutWidgets();

}

private void createWidgets() {
    searchQueryTextBox = new TextBox();

    searchButton = new Button("Search");
    searchButton.addClickHandler(new ClickHandler() {
        @Override
        public void onClick(ClickEvent event) {
            setLoading(true);
            String query = searchQueryTextBox.getText();
            service.searchTweets(query, new AsyncCallback<List<Tweet>>() {
                @Override
                public void onFailure(Throwable caught) {
                    errorLabel.setText(caught.getMessage());
                    errorLabel.setVisible(true);
                    setLoading(false);
                }

                @Override
                public void onSuccess(List<Tweet> result) {
                    resultsPanel.clear();
                    for (Tweet tweet : result) {
                        SafeHtmlBuilder builder = new SafeHtmlBuilder();
                        builder.appendHtmlConstant("<b>User: </b>");
                        builder.appendEscaped(tweet.getFrom_user());
                        builder.appendHtmlConstant("<br /><b>Created: </b>");
                        builder.appendEscaped(tweet.getCreated_at());
                        builder.appendHtmlConstant("<br /><b>Tweet: </b>");
                        builder.appendEscaped(tweet.getText());
                        builder.appendHtmlConstant("<br /><br />");
                        resultsPanel.add(new HTML(builder.toSafeHtml()));
                    }
                    setLoading(false);
                }
            });
        }
    });

    privacyPolicyButton = new Button("Privacy Policy");
    privacyPolicyButton.addClickHandler(new ClickHandler() {
        @Override
        public void onClick(ClickEvent event) {
            setLoading(true);
            service.getPrivacyPolicy(new AsyncCallback<String>() {
                @Override
                public void onFailure(Throwable caught) {
                    errorLabel.setText(caught.getMessage());
                    errorLabel.setVisible(true);
                    setLoading(false);
                }

                @Override
                public void onSuccess(String result) {
                    resultsPanel.clear();

                    // convert newlines to <br />
                    SafeHtmlBuilder builder = new SafeHtmlBuilder();
                    builder.appendEscapedLines(result);

                    resultsPanel.add(new HTML(builder.toSafeHtml()));

                    setLoading(false);
                }
            });
        }
    });

    resultsPanel = new VerticalPanel();

    errorLabel = new Label();
    errorLabel.addStyleName("errorLabel");
    errorLabel.setVisible(false);

    //image from http://loadinfo.net/
    loadingImage = new Image("loading.gif");
    loadingImage.setVisible(false);
}

private void layoutWidgets() {
    Panel panel = new VerticalPanel();

    panel.add(errorLabel);

    Panel horizPanel = new HorizontalPanel();
    horizPanel.add(searchQueryTextBox);
    horizPanel.add(searchButton);
    horizPanel.add(privacyPolicyButton);
    horizPanel.add(loadingImage);
    panel.add(horizPanel);

    panel.add(resultsPanel);

    RootPanel.get().add(panel);
}

/**
 * Updates the UI for when a RPC call is made.
 * @param loading true if an RPC call is being sent, false if not
 */
private void setLoading(boolean loading) {
    if (loading) {
        errorLabel.setVisible(false);
    }
    searchQueryTextBox.setEnabled(!loading);
    searchButton.setEnabled(!loading);
    privacyPolicyButton.setEnabled(!loading);
    loadingImage.setVisible(loading);
}
}

这是推文代码：

    package com.google.gwt.twittersearch.client;

import java.io.Serializable;

@SuppressWarnings("serial")
public class Tweet implements Serializable{
private String id;
  private String from_user;
  private String created_at;
  private String text;

  public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getFrom_user() {
        return from_user;
    }

    public void setFrom_user(String from_user) {
        this.from_user = from_user;
    }

    public String getCreated_at() {
        return created_at;
    }

    public void setCreated_at(String created_at) {
        this.created_at = created_at;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }


}

任何对此错误的见解或我可能从这里去的地方将不胜感激！

谢谢，brl

4

1 回答 1

7

您需要添加一个无参数构造函数，例如：

public class Tweet implements Serializable{

  public Tweet(){
  }

}

编辑

你在这里也需要一个

private class SearchResponse {

  public SearchResponse(){
  }
  public List<Tweet> results;
}

处理你的错误java.lang.RuntimeException: Unable to invoke no-args constructor for class

如果满足以下条件，用户定义的类是可序列化的：

  1. 该类可分配给 IsSerializable 或 java.io.Serializable，因为它实现了这些接口之一，或者因为它派生自实现这些接口之一的超类。

  2. 所有类的非最终、非瞬态实例字段都是可序列化的

  3. 该类有一个公共默认（零参数）构造函数

以上来自本教程

于 2012-08-27T21:27:59.810 回答