BufferedReader 连接未关闭

Question

我创建了一个小型抓取类，下面的方法从页面中读取文本。

但是，我发现该方法无法正确关闭连接。这会导致大量打开的连接导致我的托管公司暂停我的帐户。以下是正确的吗？

private String getPageText(String urlString) {

    String pageText = "";


        BufferedReader reader = null;
        try {
            URL url = new URL(urlString);
            reader = new BufferedReader(new InputStreamReader(url.openStream()));
            StringBuilder builder = new StringBuilder();
            int read;
            char[] chars = new char[1024];
            while ((read = reader.read(chars)) != -1)
                builder.append(chars, 0, read); 

            pageText = builder.toString();
        } catch (MalformedURLException e) {
            Log.e(CLASS_NAME, "getPageText.MalformedUrlException", e);
        } catch (IOException e) {
            Log.e(CLASS_NAME, "getPageText.IOException", e);
        } finally {
            if (reader != null)
                try {
                    reader.close();
                } catch (IOException e) {
                    Log.e(CLASS_NAME, "getPageText.IOException", e);
                }
        }
        return pageText;


}

Answer 1

您的代码在成功情况下很好，但在失败情况下可能会泄漏连接（当 http 服务器返回 4xx 或 5xx 状态代码时）。在这些情况下，HttpURLConnection 通过.getErrorStream() 而不是.getInputStream() 提供响应正文，您还应确保排空并关闭该流。

URLConnection conn = null;
BufferedReader reader = null;
try {
  conn = url.openConnection();
  reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
  // ...
} finally {
  if(reader != null) {
    // ...
  }
  if(conn instanceof HttpURLConnection) {
    InputStream err = ((HttpURLConnection)conn).getErrorStream();
    if(err != null) {
      byte[] buf = new byte[2048];
      while(err.read(buf) >= 0) {}
      err.close();
    }
  }
}

最终可能需要在其中添加另一层 try/catch，但您明白了。您应该不明确地.disconnect() 连接，除非您确定在不久的将来该主机上不会再有对 url 的请求 - disconnect() 将阻止后续请求通过管道传输现有的连接，尤其是对于 https 会大大减慢速度。

Answer 2

您只是关闭stream 而不是connection，使用以下结构：

URL u = new URL(url);
HttpURLConnection conn = (HttpURLConnection)
        u.openConnection();
conn.connect();

reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

然后：

} finally {
    if (reader != null)
       try {
           reader.close();
       } catch (IOException e) {
           Log.e(CLASS_NAME, "getPageText.IOException", e);
       }
    }

    try {
        if (conn != null) {
            conn.disconnect();
        }
    } catch (Exception ex) {}
}