HTTP status code

List of HTTP status codes: http://en.wikipedia.org/wiki/List_of_HTTP_status_codes

•  1xx Informational
•  2xx Success
•  3xx Redirection
•  4xx Client Error
•  5xx Server Error

java.net.HttpURLConnection.getResponseCode(): Gets the status code from an HTTP response message.
For example： the following codes from w w w . c ode java. net/java-se/networking/use-httpurlconnection-to-download-file-from-an-http-url

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import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * A utility that downloads a file from a URL.
 * @author www.codejava.net
 */
public class HttpDownloadUtility {
    private static final int BUFFER_SIZE = 4096;
    /**
    * Downloads a file from a URL
    * @param fileURL HTTP URL of the file to be downloaded
    * @param saveDir path of the directory to save the file
    * @throws IOException
    */
    public static void downloadFile(String fileURL, String saveDir) throws MalformedURLException, IOException{
        URL url = new URL(fileURL);
        HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
        int responseCode = httpConn.getResponseCode();
        //always check HTTP response code first
        if(responseCode == HttpURLConnection.HTTP_OK){
            String fileName = "";
            String disposition = httpConn.getHeaderField("Content-Disposition");
            String contentType = httpConn.getContentType();
            int contentLength = httpConn.getContentLength();
            if(disposition!=null){
                //extracts file name from hearder field
                int index = disposition.indexOf("filename=");
                if(index>0){
                    fileName = disposition.substring(index + 10, disposition.length() - 1 );
                }
            } else {
                // extracts file name from URL
                fileName = fileURL.substring(fileURL.lastIndexOf("/")+1, fileURL.length());
            }
            System.out.println("Content-Type = "+contentType);
            System.out.println("Content-Disposition = "+disposition);
            System.out.println("Content-Length = "+ contentLength);
            System.out.println("fileName = "+fileName);
           
            // opens input stream from the HTTP connection
            InputStream inputStream = httpConn.getInputStream();
            String saveFilePath = saveDir + File.separator + fileName;
            // opens an output stream to save into file
            FileOutputStream outputStream = new FileOutputStream(saveFilePath);
           
            int bytesRead = -1;
            byte[] buffer = new byte[BUFFER_SIZE];
            while((bytesRead=inputStream.read(buffer))!=-1){
                outputStream.write(buffer,0,bytesRead);
            }
            outputStream.close();
            inputStream.close();
           
            System.out.println("File downloaded");
           
        }else{
            System.out.println("No file to download. Server replied HTTP code: "+responseCode);
        }
        httpConn.disconnect();
    }
   
}


h t t p : / / z h . w i k i pedia.org/wiki/HTTP%E7%8A%B6%E6%80%81%E7%A0%81
 h  t t p : / / w w w .c n b l o g s . c o m / tankxiao/archive/2013/01/08/2818542.html#WhatsStatusCode