java - 在 Android 的 AsyncTask 中使用 HttpClient 时出现 FatalException

Question

我在这里不知所措。我正在尝试使用从 RESTful API 提取的数据来填充我的 Activity 中的列表。我已经创建了使用 Apache HttpClient 库 (org.apache.http.client) 与 API 进行(成功)对话的 API 层。然而，当我尝试将 Activity 与 API 层连接(通过 AsyncTask)时，灾难就发生了。我从有问题的代码中删除了 API 层，而是嵌入了我能想到的最简单的示例来尝试隔离问题(但无济于事)。这是有问题的代码:

public class MyActivity extends Activity {

@Override
protected void onCreate( Bundle savedInstanceState ) {

    super.onCreate( savedInstanceState );
    setContentView( R.layout.main );
}

@Override
protected void onResume() {

    super.onResume();
    new GetEventsTask().execute();
}

private class GetEventsTask extends AsyncTask<Object, Integer, List<IEvent>> {

    @Override
    protected List<IEvent> doInBackground( Object... params ) {

        fetch();
        return null;
    }

    @Override
    protected void onPostExecute( List<IEvent> events ) {

        Toast.makeText( getApplicationContext(), "Success", Toast.LENGTH_SHORT ).show();
    }

    private void fetch() {
        CloseableHttpClient client = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost( "https://someurl.com/login" );

        List<NameValuePair> data = new ArrayList<NameValuePair>();
        data.add( new BasicNameValuePair( "username", "hai" ) );
        data.add( new BasicNameValuePair( "password", "kthxbye" ) );

        try {
            httpPost.setEntity( new UrlEncodedFormEntity( data ) );
            CloseableHttpResponse response = client.execute( httpPost );
        } catch( Exception e ) {
            Toast.makeText( getApplicationContext(), "Caught Exception", Toast.LENGTH_SHORT ).show();
        }
    }
}

这是堆栈跟踪:

10-16 19:36:04.264: ERROR/AndroidRuntime(633): FATAL EXCEPTION: AsyncTask #1
    java.lang.RuntimeException: An error occured while executing doInBackground()
    at android.os.AsyncTask$3.done(AsyncTask.java:200)
    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
    at java.lang.Thread.run(Thread.java:1019)
    Caused by: java.lang.ExceptionInInitializerError
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager$InternalConnectionFactory.<init>(PoolingHttpClientConnectionManager.java:487)
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:147)
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:136)
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:112)
    at org.apache.http.impl.client.HttpClientBuilder.build(HttpClientBuilder.java:727)
    at org.apache.http.impl.client.HttpClients.createDefault(HttpClients.java:58)
    at ca.redacted.app.MyActivity$GetEventsTask.fetch(MyActivity.java:70)
    at ca.redacted.app.MyActivity$GetEventsTask.doInBackground(MyActivity.java:49)
    at ca.redacted.app.MyActivity$GetEventsTask.doInBackground(MyActivity.java:44)
    at android.os.AsyncTask$2.call(AsyncTask.java:185)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
    ... 4 more
    Caused by: java.lang.ExceptionInInitializerError
    at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:72)
    at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:84)
    at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<clinit>(ManagedHttpClientConnectionFactory.java:59)
    ... 15 more
    Caused by: java.lang.NoSuchFieldError: org.apache.http.message.BasicLineFormatter.INSTANCE
    at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:52)
    at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:56)
    at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<clinit>(DefaultHttpRequestWriterFactory.java:46)
    ... 18 more

我对 Android 编程还比较陌生(并且有一段时间没有接触过 Java)，因此非常感谢您的帮助。

已更新 基于调试运行，这是抛出 FatalException 的行

CloseableHttpClient 客户端 = HttpClients.createDefault();

再次更新

切换到使用 Android 提供的 DefaultHttpClient 实现解决了问题(以防其他人在使用 Apache 版本时遇到麻烦)。仍然不知道是什么让我对其他图书馆感到悲伤。

Answer 1

我假设您已经添加了 apache 库，因为 HttpClients 不是内置在 Android 代码中，请参阅 here .您收到运行时异常但没有编译异常的原因我认为是因为您的库未随应用程序导出。

ExceptionInInitializerError

意味着它无法加载指向此处的静态类(HttpClients):

CloseableHttpClient client = HttpClients.createDefault();

为了解决这个问题，您必须在 Eclipse 中使用应用程序导出外部 apache 库:

Project-> config build path-> select lib to export.

除此之外，@codeMagic 指出您的 catch 子句不能使用 Toast，因为它应该在 UI 线程上运行。这不会导致您的异常，因为您当前的代码没有到达 try 子句，但请注意。