Example: Retrying SQL Queries for Applications

//gsjdbc4.jar is used as an example. If gsjdbc200.jar is used, replace the class name org.postgresql with com.huawei.gauss200.jdbc and replace the URL prefix jdbc:postgresql with jdbc:gaussdb.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * 
 *
 */

class ExitHandler extends Thread {
    private Statement cancel_stmt = null;

    public ExitHandler(Statement stmt) {
        super("Exit Handler");
        this.cancel_stmt = stmt;
    }
    public void run() {
        System.out.println("exit handle");
        try {
            this.cancel_stmt.cancel();
        } catch (SQLException e) {
            System.out.println("cancel query failed.");
            e.printStackTrace();
        }
    }
}

public class SQLRetry {
  //Establish a connection to the database.
   public static Connection GetConnection(String username, String passwd) {
     String driver = "org.postgresql.Driver";
     String sourceURL = "jdbc:postgresql://10.131.72.136:8000/gaussdb";
     Connection conn = null;
     try {
      //Load the database driver.
       Class.forName(driver).newInstance();
     } catch (Exception e) {
       e.printStackTrace();
       return null;
     }

     try {
      //Establish a connection to the database.
       conn = DriverManager.getConnection(sourceURL, username, passwd);
       System.out.println("Connection succeed!");
     } catch (Exception e) {
       e.printStackTrace();
       return null;
     }

     return conn;
}
 
  //Run an ordinary SQL statement. Create a jdbc_test1 table.
   public static void CreateTable(Connection conn) {
     Statement stmt = null;
     try {
       stmt = conn.createStatement();

       // add ctrl+c handler
       Runtime.getRuntime().addShutdownHook(new ExitHandler(stmt));

      // Run an ordinary SQL statement.
       int rc2 = stmt
          .executeUpdate("DROP TABLE if exists jdbc_test1;");

       int rc1 = stmt
          .executeUpdate("CREATE TABLE jdbc_test1(col1 INTEGER, col2 VARCHAR(10));");

       stmt.close();
     } catch (SQLException e) {
       if (stmt != null) {
         try {
           stmt.close();
         } catch (SQLException e1) {
           e1.printStackTrace();
         }
       }
       e.printStackTrace();
     }
   }

  //Run the preprocessing statement to insert data in batches.
   public static void BatchInsertData(Connection conn) {
     PreparedStatement pst = null;

     try {
      //Generate a prepared statement.
       pst = conn.prepareStatement("INSERT INTO jdbc_test1 VALUES (?,?)");
       for (int i = 0; i < 100; i++) {
        //Add parameters.
         pst.setInt(1, i);
         pst.setString(2, "data " + i);
         pst.addBatch();
       }
      //Perform batch processing.
       pst.executeBatch();
       pst.close();
     } catch (SQLException e) {
       if (pst != null) {
         try {
           pst.close();
         } catch (SQLException e1) {
         e1.printStackTrace();
         }
       }
       e.printStackTrace();
     }
   }
 
  //Run the precompilation statement to update data.
   private static boolean QueryRedo(Connection conn){
     PreparedStatement pstmt = null;
     boolean retValue = false;
     try {
       pstmt = conn
           .prepareStatement("SELECT col1 FROM jdbc_test1 WHERE col2 = ?");
 
           pstmt.setString(1, "data 10");
           ResultSet rs = pstmt.executeQuery();

           while (rs.next()) {
               System.out.println("col1 = " + rs.getString("col1"));
           }
           rs.close();
 
       pstmt.close();
        retValue = true;
      } catch (SQLException e) {
       System.out.println("catch...... retValue " + retValue);
       if (pstmt != null) {
         try {
          pstmt.close();
        } catch (SQLException e1) {
          e1.printStackTrace();
         }
       }
       e.printStackTrace();
     }
 
      System.out.println("finesh......"); 
     return retValue;
   }

//Run a query statement and retry upon a failure. The number of retry times can be configured.
   public static void ExecPreparedSQL(Connection conn) throws InterruptedException {
         int maxRetryTime = 50;
         int time = 0;
         String result = null;
         do {
             time++;
             try {
  System.out.println("time:" + time);
  boolean ret = QueryRedo(conn);
  if(ret == false){
   System.out.println("retry, time:" + time);
   Thread.sleep(10000); 
   QueryRedo(conn);
  }
             } catch (Exception e) {
                 e.printStackTrace();
             }
         } while (null == result && time < maxRetryTime); 
 
   }

   /**
   * Main process. Call static methods one by one.
    * @param args
  * @throws InterruptedException 
   */
   public static void main(String[] args) throws InterruptedException {
    //Establish a connection to the database.
     Connection conn = GetConnection("testuser", "test@123");

    //Create a table.
     CreateTable(conn);

    //Insert data in batches.
     BatchInsertData(conn);

    //Run the precompilation statement to update data.
     ExecPreparedSQL(conn);

    //Disconnect from the database.
     try {
       conn.close();
     } catch (SQLException e) {
       e.printStackTrace();
     }

   }

 }