import java.net.HttpURLConnection;
import java.net.URL;
 
import org.junit.Assert;
import org.junit.Test;
 
public class GetRedirectUrlTest {
  @Test
  public void test_getRedirectUrl() throws Exception {
    String url="http://www.baidu.com/link?url=ByBJLpHsj5nXx6DESXbmMjIrU5W4Eh0yg5wCQpe3kCQMlJK_RJBmdEYGm0DDTCoTDGaz7rH80gxjvtvoqJuYxK";
    String expectUrl="http://www.zhihu.com/question/20583607/answer/16597802";
    String redictURL = getRedirectUrl(url);
    Assert.assertEquals(expectUrl, redictURL);
  }
  
  /**
   * 獲取重定向地址
   * @param path
   * @return
   * @throws Exception
   */
  private String getRedirectUrl(String path) throws Exception {
    HttpURLConnection conn = (HttpURLConnection) new URL(path)
        .openConnection();
    conn.setInstanceFollowRedirects(false);
    conn.setConnectTimeout(5000);
    return conn.getHeaderField("Location");
  }
}

/**
   * 處理跳轉鏈接，獲取重定向地址
   * @param url  源地址
   * @return   目標網頁的絕對地址
   */
  public String getAbsUrl(String url){
    CloseableHttpClient httpclient = HttpClients.createDefault();
    HttpClientContext context = HttpClientContext.create();
    HttpGet httpget = new HttpGet(url);
    CloseableHttpResponse response = null;
    String absUrl = null;
    try {
      response = httpclient.execute(httpget, context);
      HttpHost target = context.getTargetHost();
      List<URI> redirectLocations = context.getRedirectLocations();
      URI location = URIUtils.resolve(httpget.getURI(), target, redirectLocations);
      System.out.println("Final HTTP location: " + location.toASCIIString());
      absUrl = location.toASCIIString();     
    }catch(IOException e){
      e.printStackTrace();
    }catch (URISyntaxException e) {     
      e.printStackTrace();
    }finally {
      try {
        httpclient.close();
        response.close();
      } catch (IOException e) {        
        e.printStackTrace();
      }
    }
    return absUrl;
  }