November 2010 Archives

Gson Exception: No-args constructor for class XXX does not exit.

By philipz on November 27, 2010 11:07 AM | No TrackBacks
Use JDO and RESTful web services at GAE. Usually need to parser JSON format string by Gson. But, some JDO class doesn't have No-args constructor, public YourClass(){}, and therefore the gson instance will throw out exception, No-args constructor for class XXX does not exit.
There are two ways to fix this problem:
One, add No-args constructor in the JDO class.
The other is use InstanceCreator to instead a no-argument constructor.
Example:

public class YourClassInstanceCreator implements InstanceCreator<YourClass> {
 public YourClass createInstance(Type type) {
   return new YourClass(null, null, null, null);
 }
}

 Then build the gson instance through GsonBuilder, like
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(YourClass.class, new YourClassInstanceCreator());
Gson gson = builder.create();
stoken = gson.fromJson(json, YourClass.class);

Call Plurk API by HttpClient 4

By philipz on November 24, 2010 10:13 AM | 1 TrackBack

之前的噗浪(Plurk)期貨即時訊息文章中，說道IM發噗會有掉噗情況，目前改用Plurk Api後，情況有改善。程式如下：

import java.io.IOException;

import java.net.URLEncoder;


import org.apache.http.HttpHost;

import org.apache.http.HttpResponse;

import org.apache.http.HttpStatus;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.CookieStore;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.conn.params.ConnRoutePNames;

import org.apache.http.impl.client.DefaultHttpClient;

import org.apache.http.util.EntityUtils;


public class PlurkApi {


private static final String API_KEY = "KEYSTRING";

static boolean use_proxy = false;

static String PROXY_NAME = "proxy.hinet.net";

static int PROXY_PORT = 80;

static CookieStore cookiestore;

static final String username= "youraccount";

static final String password= "yourpassword";

private volatile static PlurkApi plurk;

private PlurkApi(){}

public static PlurkApi getInstance(){

if (plurk == null) {

synchronized (PlurkApi.class){

if (plurk == null) {

plurk = new PlurkApi();

}

}

}

return plurk;

}


    public static String getApiUri(String uri) {

        return "http://www.plurk.com/API" + uri;

    }


    public final static void main(String[] args) {

     PlurkApi p = PlurkApi.getInstance();

     p.plurkAdd("API測試111111！");

     p.logout();

    }

    

    public String login() {

     DefaultHttpClient httpclient = new DefaultHttpClient();

        if (use_proxy) {

HttpHost proxy = new HttpHost(PROXY_NAME, PROXY_PORT);

httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY,

proxy);

}

        

        HttpGet httpget = new HttpGet(getApiUri("/Users/login?"+

                            "api_key=" + API_KEY + "&" +

                            "username=" + username + "&" +

                            "password=" + password

                          ));

        HttpResponse response = null;

String responseString = null;

try {

response = httpclient.execute(httpget);

if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {

cookiestore = httpclient.getCookieStore();

responseString = EntityUtils.toString(response.getEntity());

// 如果回傳是 200 OK 的話才輸出

// System.out.println(responseString);

//

} else {

System.out.println(response.getStatusLine());

responseString = EntityUtils.toString(response.getEntity());

System.out.println(responseString);

}

} catch (ClientProtocolException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

httpclient.getConnectionManager().shutdown();

return responseString;

    }

    

    public String plurkAdd(String url) {

     PlurkApi p = PlurkApi.getInstance();

     if (cookiestore == null)

     p.login();

     DefaultHttpClient httpclient = new DefaultHttpClient();

        if (use_proxy) {

HttpHost proxy = new HttpHost(PROXY_NAME, PROXY_PORT);

httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY,

proxy);

}

        httpclient.setCookieStore(cookiestore);

       

        HttpResponse response = null;

String responseString = null;

try {

String content = URLEncoder.encode(url, "UTF-8");

HttpGet httpget = new HttpGet(getApiUri("/Timeline/plurkAdd?"+

               "api_key=" + API_KEY + "&" +

               "content=" + content + "&" +

               "qualifier=" + "says" + "&" +

               "lang=tr_ch"));

response = httpclient.execute(httpget);

if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {

cookiestore = httpclient.getCookieStore();

responseString = EntityUtils.toString(response.getEntity());

// 如果回傳是 200 OK 的話才輸出

// System.out.println(responseString);

//

} else {

System.out.println(response.getStatusLine());

responseString = EntityUtils.toString(response.getEntity());

System.out.println(responseString);

}

} catch (ClientProtocolException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

httpclient.getConnectionManager().shutdown();

return responseString;

    }


    public String logout() {

     PlurkApi p = PlurkApi.getInstance();

     if (cookiestore == null)

     p.login();

     DefaultHttpClient httpclient = new DefaultHttpClient();

        if (use_proxy) {

HttpHost proxy = new HttpHost(PROXY_NAME, PROXY_PORT);

httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY,

proxy);

}

        httpclient.setCookieStore(cookiestore);

        HttpResponse response = null;

String responseString = null;

try {

HttpGet httpget = new HttpGet(getApiUri("/Users/logout?"+

                     "api_key=" + API_KEY));

response = httpclient.execute(httpget);

if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {

cookiestore = httpclient.getCookieStore();

responseString = EntityUtils.toString(response.getEntity());

// 如果回傳是 200 OK 的話才輸出

// System.out.println(responseString);

//

} else {

System.out.println(response.getStatusLine());

responseString = EntityUtils.toString(response.getEntity());

System.out.println(responseString);

}

} catch (ClientProtocolException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

httpclient.getConnectionManager().shutdown();

return responseString;

    }

}

如何遠端呼叫需特定權限的Google App Engine service

By philipz on November 20, 2010 3:26 PM | No TrackBacks

參考：Accessing a security-enabled Google App Engine service from a Java client

如果您撰寫一個GAE servlet，卻是特定權限，如admin，才能執行的service，透過人工輸入網頁是沒多大問題，但如果要用程式去遠端呼叫，卻需要先取得一個token，利用Google Data API的GoogleAuthTokenFactory，呼叫程式如下：

import java.io.IOException;

import java.io.UnsupportedEncodingException;

import java.net.URLEncoder;

import java.util.logging.Logger;


import org.apache.http.HttpHost;

import org.apache.http.HttpResponse;

import org.apache.http.HttpStatus;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.CookieStore;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.client.params.ClientPNames;

import org.apache.http.client.params.CookiePolicy;

import org.apache.http.conn.params.ConnRoutePNames;

import org.apache.http.impl.client.DefaultHttpClient;

import org.apache.http.util.EntityUtils;


import com.google.gdata.client.GoogleAuthTokenFactory;

import com.google.gdata.util.AuthenticationException;


public class AppEngineAPI {

static CookieStore cookiestore;

static final String loginUrl = "http://yours.appspot.com/_ah/login?continue=";

static boolean use_proxy = false;

static String PROXY_NAME = "proxy.hinet.net";

static int PROXY_PORT = 80;

static final String serviceUrl = "http://yours.appspot.com/admin/service?";

static final String username = "your account";

static final String password = "your password";

static final String serviceName = "ah";

static final GoogleAuthTokenFactory factory = new GoogleAuthTokenFactory(serviceName, "", null);

static String token; 

private static final Logger log = Logger.getLogger(AppEngineAPI.class

.getName());


public static void main(String[] args) {

try {

String token = factory.getAuthToken(username, password, null, null, serviceName, "");

String serviceUrl1 = serviceUrl + "a=a&b=b";

String loginUrl1 = loginUrl + URLEncoder.encode(serviceUrl1, "UTF-8") + "&auth=" + token;

httpget(loginUrl1);

} catch (AuthenticationException e) {

log.warning(e.toString());

e.printStackTrace();

} catch (UnsupportedEncodingException e) {

log.warning(e.toString());

e.printStackTrace();

}

}

public static String httpget(String url) {

DefaultHttpClient httpclient = new DefaultHttpClient();

if (use_proxy) {

HttpHost proxy = new HttpHost(PROXY_NAME, PROXY_PORT);

httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY,

proxy);

}


HttpGet httpget = new HttpGet(url);

// Override the default policy for this request


httpget.getParams().setParameter(ClientPNames.COOKIE_POLICY,

CookiePolicy.BROWSER_COMPATIBILITY);

HttpResponse response = null;

String responseString = null;

try {

response = httpclient.execute(httpget);

if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {

cookiestore = httpclient.getCookieStore();

responseString = EntityUtils.toString(response.getEntity());

// 如果回傳是 200 OK 的話才輸出

// System.out.println(responseString);

//

} else {

System.out.println(response.getStatusLine());

}


} catch (ClientProtocolException e) {

log.warning(e.toString());

} catch (IOException e) {

log.warning(e.toString());

}

httpclient.getConnectionManager().shutdown();

return responseString;

}

}

相關知識：維基百科OpenID、OAuth，Google文件OpenID、OAuth。

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