Accessing Spark SQL Sample Projects Through JDBC (Java)

Function

The JDBC API of the user-defined client is used to submit a data analysis task and return the results.

Sample Code

1. Define an SQL statement. SQL must be a single statement and cannot contain semicolons ";". The following is an example:

   ArrayList<String> sqlList = new ArrayList<String>();
   sqlList.add("CREATE TABLE CHILD (NAME STRING, AGE INT) ROW FORMAT DELIMITED FIELDS TERMINATED BY ','");
   sqlList.add("LOAD DATA LOCAL INPATH '/home/data' INTO TABLE CHILD");
   sqlList.add("SELECT * FROM child");
   sqlList.add("DROP TABLE child");
   executeSql(url, sqlList);

   

   The data file in the sample project must be placed in the home directory of the host where the JDBCServer is located.

2. Concatenate the JDBC URL.

   Configuration config = new Configuration();
   config.addResource(new Path(args[0]));
   String zkUrl = config.get("spark.deploy.zookeeper.url");
   
   String zkNamespace = null;
   zkNamespace = fileInfo.getProperty("spark.thriftserver.zookeeper.namespace");
   if (zkNamespace != null) {
      //Remove redundant characters from configuration items
      zkNamespace = zkNamespace.substring(1);
   }
   
   StringBuilder sb = new StringBuilder("jdbc:hive2://"
           + zkUrl
           + "/;serviceDiscoveryMode=zooKeeper;"
           + "zooKeeperNamespace="
           + zkNamespace + ";");
   String url = sb.toString();

3. Load the Hive JDBC driver.

   Class.forName("org.apache.hive.jdbc.HiveDriver").newInstance();

4. Obtain the JDBC connection, execute the HiveQL statement, return the queried column name and results to the console, and close the JDBC connection.

   The zk.quorum in the connection string can be replaced by spark.deploy.zookeeper.url in the configuration file.

   In network congestion, configure the timeout of the connection between the client and JDBCServer to avoid the anomaly of the client due to timeless wait of the return from the server. The configuration method is as follows:

   Before using the DriverManager.getConnection method to obtain the JDBC connection, add the DriverManager.setLoginTimeout(n) method to configure a timeout interval. n indicates the timeout interval for waiting for the return result from the server. The unit is second, the type is Int, and the default value is 0 (indicating never timing out).

   static void executeSql(String url, ArrayList<String> sqls) throws ClassNotFoundException, SQLException {
           try {
               Class.forName("org.apache.hive.jdbc.HiveDriver").newInstance();
           } catch (Exception e) {
               e.printStackTrace();
           }
           Connection connection = null;
           PreparedStatement statement = null;
   
           try {
               connection = DriverManager.getConnection(url);
               for (int i = 0 ; i < sqls.size(); i++) {
                   String sql = sqls.get(i);
                   System.out.println("---- Begin executing sql: " + sql + " ----");
                   statement = connection.prepareStatement(sql);
                   ResultSet result = statement.executeQuery();
                   ResultSetMetaData resultMetaData = result.getMetaData();
                   Integer colNum = resultMetaData.getColumnCount();
                   for (int j = 1; j <= colNum; j++) {
                       System.out.println(resultMetaData.getColumnLabel(j) + "\t");
                   }
                   System.out.println();
   
                   while (result.next()) {
                       for (int j = 1; j <= colNum; j++){
                           System.out.println(result.getString(j) + "\t");
                       }
                       System.out.println();
                   }
                   System.out.println("---- Done executing sql: " + sql + " ----");
               }
   
   
           } catch (Exception e) {
               e.printStackTrace();
           } finally {
               if (null != statement) {
                   statement.close();
               }
               if (null != connection) {
                   connection.close();
               }
           }
       }