Detailed explanation of Java sending post method

Summarize the method of sending post by java using http under 1:

1. The post request is used to send parameters in json format:

/**
   * post Request (used to request json Format parameters) 
   *
   * @param url   Address 
   * @param params json Parameters of the format 
   * @return
   */
  public static String doPost(String url, String params) throws Exception {
 
    CloseableHttpClient httpclient = HttpClients.createDefault();
    HttpPost httpPost = new HttpPost( url );//  Create httpPost
    httpPost.setHeader( "Accept", "application/json" );
    httpPost.setHeader( "Content-Type", "application/json" );
    String charSet = "UTF-8";
    StringEntity entity = new StringEntity( params, charSet );
    httpPost.setEntity( entity );
    CloseableHttpResponse response = null;
 
    try {
 
      response = httpclient.execute( httpPost );
      StatusLine status = response.getStatusLine();
      int state = status.getStatusCode();
      if (state == HttpStatus.SC_OK) {
        HttpEntity responseEntity = response.getEntity();
        String jsonString = EntityUtils.toString( responseEntity );
        return jsonString;
      } else {
        logger.error( " Request return :" + state + "(" + url + ")" );
      }
    } finally {
      if (response != null) {
        try {
          response.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
      try {
        httpclient.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
    return null;
  }

2. Parameters for sending key-value format

/**
   * post Request ( Used for key-value Parameters of the format )
   *
   * @param url
   * @param params
   * @return
   */
  public static String doPost(String url, Map params) {
 
    BufferedReader in = null;
    try {
      //  Definition HttpClient
      HttpClient client = new DefaultHttpClient();
      //  Instantiation HTTP Method 
      HttpPost request = new HttpPost();
      request.setURI( new URI( url ) );
 
      // Setting parameters 
      List<NameValuePair> nvps = new ArrayList<NameValuePair>();
      for (Iterator iter = params.keySet().iterator(); iter.hasNext(); ) {
        String name = (String) iter.next();
        String value = String.valueOf( params.get( name ) );
        nvps.add( new BasicNameValuePair( name, value ) );
 
        //System.out.println(name +"-"+value);
      }
      request.setEntity( new UrlEncodedFormEntity( nvps, HTTP.UTF_8 ) );
 
      HttpResponse response = client.execute( request );
      int code = response.getStatusLine().getStatusCode();
      if (code == 200) {  // Request succeeded 
        in = new BufferedReader( new InputStreamReader( response.getEntity()
            .getContent(), "utf-8" ) );
        StringBuffer sb = new StringBuffer( "" );
        String line = "";
        String NL = System.getProperty( "line.separator" );
        while ((line = in.readLine()) != null) {
          sb.append( line + NL );
        }
        in.close();
 
        return sb.toString();
      } else {  //
        System.out.println( " Status code: " + code );
        return null;
      }
    } catch (Exception e) {
      e.printStackTrace();
      return null;
    }
  }

Third, send an get request

/**
   * get Request 
   *
   * @return
   */
  public static String doGet(String url) {
    try {
      HttpClient client = new DefaultHttpClient();
      // Send get Request 
      HttpGet request = new HttpGet( url );
      HttpResponse response = client.execute( request );
      /** The request was sent successfully and received a response **/
      if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
        /** Read the returned from the server json String data **/
        String strResult = EntityUtils.toString( response.getEntity() );
        return strResult;
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
 
    return null;
  }