java - HttpResponse 使用 android 问题 : execute always causes exception?

Question

我一直在从事一个 Android 项目，现在我想向一些 API 询问信息。看起来这应该是非常基础的!

这是我的代码的一般要点:

private InputStream retrieveStream2(String url)
{
    DefaultHttpClient client = new DefaultHttpClient();

    HttpGet getRequest = new HttpGet(url);
    System.out.println("getRequest == " + getRequest);
    try {


        HttpResponse getResponse = client.execute(getRequest);//here is teh problem
        final int statusCode = getResponse.getStatusLine().getStatusCode();


        if (statusCode != HttpStatus.SC_OK)
        {
            Log.w(getClass().getSimpleName(),
                    "Error " + statusCode + " for URL " + url);
            return null;
        }

        HttpEntity getResponseEntity = getResponse.getEntity();
        return getResponseEntity.getContent();

    }
    catch (Exception e)
    {
        getRequest.abort();
        Log.w(getClass().getSimpleName(), "Error for URL, YO " + url, e);
    }
    return null;
}

其中 url 变量是字符串“http://search.twitter.com/search.json?q=javacodegeeks”。

如您所见，该站点上有一些不错的 JSON 信息；我的问题是每次调用“client.execute(getRequest);”时，程序都会抛出并捕获异常。没用!

我听说过两件事:

1) 您必须为模拟器/设备设置权限才能使用互联网! -- 我想我涵盖了这一点，但也许我做错了! 在我添加的 androidmanifest.xml 中

< uses-permission android:name="android.permission.INTERNET" >< /uses-permission>

就是这样。

2)(我不太确定)您不能在“ui”线程中启动“网络”线程。我不完全确定这意味着什么，但我继续学习了一些关于 Android 线程、处理程序和 AsyncTasks 的教程。这里:请查看我遵循的 AsyncTask 教程下的代码:

http://www.vogella.de/articles/AndroidPerformance/article.html

跟着AsyncTask的教程，发现还是有同样的问题--

行:HttpGet httpGet = new HttpGet(url)总是抛出异常，就像以前一样。

这是我尝试使用上面的线程教程时的 logcat:

02-27 20:43:28.565: I/ActivityManager(92): START {cmp=com.Prometheus.R1/.JsonParsingActivity} from pid 574
02-27 20:43:28.565: W/WindowManager(92): Failure taking screenshot for (180x300) to layer 21010
02-27 20:43:28.896: I/System.out(574): pre execute
02-27 20:43:29.236: I/ActivityManager(92): Displayed com.Prometheus.R1/.JsonParsingActivity: +638ms
02-27 20:43:29.329: I/ARMAssembler(35): generated scanline__00000077:03010104_00008001_00000000 [ 89 ipp] (110 ins) at [0x40fad6a8:0x40fad860] in 7204915 ns
02-27 20:43:30.016: W/System.err(574): java.net.UnknownHostException: Unable to resolve host "search.twitter.com": No address associated with hostname
02-27 20:43:30.016: W/System.err(574):  at java.net.InetAddress.lookupHostByName(InetAddress.java:426)
02-27 20:43:30.026: W/System.err(574):  at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
02-27 20:43:30.026: W/System.err(574):  at java.net.InetAddress.getAllByName(InetAddress.java:220)
02-27 20:43:30.026: W/System.err(574):  at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
02-27 20:43:30.036: W/System.err(574):  at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
02-27 20:43:30.036: W/System.err(574):  at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
02-27 20:43:30.046: W/System.err(574):  at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
02-27 20:43:30.046: W/System.err(574):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
02-27 20:43:30.046: W/System.err(574):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
02-27 20:43:30.055: W/System.err(574):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
02-27 20:43:30.055: W/System.err(574):  at com.Prometheus.R1.JsonParsingActivity$DownloadWebPageTask.doInBackground(JsonParsingActivity.java:88)
02-27 20:43:30.055: W/System.err(574):  at com.Prometheus.R1.JsonParsingActivity$DownloadWebPageTask.doInBackground(JsonParsingActivity.java:1)
02-27 20:43:30.055: W/System.err(574):  at android.os.AsyncTask$2.call(AsyncTask.java:264)<br/>
02-27 20:43:30.066: W/System.err(574):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
02-27 20:43:30.066: W/System.err(574):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)<br/>
02-27 20:43:30.066: W/System.err(574):  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
02-27 20:43:30.076: W/System.err(574):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
02-27 20:43:30.076: W/System.err(574):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
02-27 20:43:30.087: W/System.err(574):  at java.lang.Thread.run(Thread.java:856)
02-27 20:43:30.108: W/System.err(574): Caused by: libcore.io.GaiException: getaddrinfo failed: EAI_NODATA (No address associated with hostname)
02-27 20:43:30.116: W/System.err(574):  at libcore.io.Posix.getaddrinfo(Native Method)
02-27 20:43:30.116: W/System.err(574):  at libcore.io.ForwardingOs.getaddrinfo(ForwardingOs.java:55)
02-27 20:43:30.126: W/System.err(574):  at java.net.InetAddress.lookupHostByName(InetAddress.java:411)
02-27 20:43:30.126: W/System.err(574):  ... 18 more
02-27 20:43:30.136: I/System.out(574): Except thrown by url http://search.twitter.com/search.json?q=javacodegeeks, .... 
02-27 20:43:30.136: I/System.out(574): response =

如您所见，异常是 UnknownHostException:
“ava.net.UnknownHostException:无法解析主机“search.twitter.com”:没有与主机名关联的地址”
但我不认为该网站是 Not Acceptable ...

谁能告诉我发生了什么事以及我需要做什么才能度过难关？

Answer 1

检查你的 list 的权限，确保你已经添加了这个:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.INTERNET"/>