Example: Retrying SQL Queries for Applications

// There will be security risks if the username and password used for authentication are directly written into code. It is recommended that the username and password be stored in the configuration file or environment variables (the password must be stored in ciphertext and decrypted when being used) to ensure security.
// In this example, the username and password are stored in environment variables. Before running this example, set environment variables EXAMPLE_USERNAME_ENV and EXAMPLE_PASSWORD_ENV in the local environment (set the environment variable names based on the actual situation).
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 {
   // Create a database connection.
   public static Connection GetConnection(String username, String passwd) {
     String driver = "org.postgresql.Driver";
     String sourceURL = "jdbc:postgresql://$ip:$port/postgres";
     Connection conn = null;
     try {
       // Load the database driver.
       Class.forName(driver).newInstance();
     } catch (Exception e) {
       e.printStackTrace();
       return null;
     }

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

     return conn;
}
 
   // Run a common SQL statement to create the jdbc_test1 table.
   public static void CreateTable(Connection conn) {
     Statement stmt = null;
     try {
       stmt = conn.createStatement();

       
       Runtime.getRuntime().addShutdownHook(new ExitHandler(stmt));

       // Run a common 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 a prepared 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 a prepared 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;
   }

   // Configure the number of retry attempts for the retry of a query statement upon a failure.
   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 {
     // Create a database connection.
     String userName = System.getenv("EXAMPLE_USERNAME_ENV");
     String password = System.getenv("EXAMPLE_PASSWORD_ENV");
     Connection conn = GetConnection(userName, password);

     // Create a table.
     CreateTable(conn);

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

     // Run a prepared statement to update data.
     ExecPreparedSQL(conn);

     // Close the connection to the database.
     try {
       conn.close();
     } catch (SQLException e) {
       e.printStackTrace();
     }

   }

 }