Example 1: Importing and Exporting Data Through Local Files

When Java is used for secondary development based on openGauss, you can use the CopyManager interface to export data from the database to a local file or import a local file to the database by streaming. The file can be in CSV or TEXT format.

The sample program is as follows. Load the openGauss JDBC driver before executing it.

import java.sql.Connection; 
import java.sql.DriverManager; 
import java.io.IOException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.sql.SQLException; 
import org.postgresql.copy.CopyManager; 
import org.postgresql.core.BaseConnection;
 
public class Copy{ 

     public static void main(String[] args) 
     { 
      String urls = new String("jdbc:postgresql://localhost:8000/postgres"); // URL of the database
      String username = new String("username");            // Username
      String password = new String("passwd");             // Password
      String tablename = new String("migration_table"); // Table information
      String tablename1 = new String("migration_table_1"); // Table information
      String driver = "org.postgresql.Driver"; 
      Connection conn = null; 
      
      try { 
          Class.forName(driver); 
          conn = DriverManager.getConnection(urls, username, password);         
      } catch (ClassNotFoundException e) { 
           e.printStackTrace(System.out); 
      } catch (SQLException e) { 
           e.printStackTrace(System.out); 
      } 
      
      // Export data from the migration_table table to the d:/data.txt file.
      try {
          copyToFile(conn, "d:/data.txt", "(SELECT * FROM migration_table)");
      } catch (SQLException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      } catch (IOException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      }    
      // Import data from the d:/data.txt file to the migration_table_1 table.
      try {
          copyFromFile(conn, "d:/data.txt", tablename1);
      } catch (SQLException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      } catch (IOException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      }  

      // Export data from the migration_table_1 table to the d:/data1.txt file.
      try {
          copyToFile(conn, "d:/data1.txt", tablename1);
      } catch (SQLException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      } catch (IOException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      }        
  } 

  public static void copyFromFile(Connection connection, String filePath, String tableName)   
         throws SQLException, IOException {  
       
     FileInputStream fileInputStream = null;  
   
     try {  
         CopyManager copyManager = new CopyManager((BaseConnection)connection);  
         fileInputStream = new FileInputStream(filePath);  
         copyManager.copyIn("COPY " + tableName + " FROM STDIN with (" + "DELIMITER"+"'"+ delimiter +  "'" + "ENCODING " + "'" + encoding + "')", fileInputStream);                        
     } finally {  
         if (fileInputStream != null) {  
             try {  
                 fileInputStream.close();  
             } catch (IOException e) {  
                 e.printStackTrace();  
             }  
         }  
     }  
 }  
     public static void copyToFile(Connection connection, String filePath, String tableOrQuery)   
          throws SQLException, IOException {  
        
      FileOutputStream fileOutputStream = null;  
   
      try {  
          CopyManager copyManager = new CopyManager((BaseConnection)connection);  
          fileOutputStream = new FileOutputStream(filePath);  
          copyManager.copyOut("COPY " + tableOrQuery + " TO STDOUT", fileOutputStream);  
      } finally {  
          if (fileOutputStream != null) {  
              try {  
                  fileOutputStream.close();  
              } catch (IOException e) {  
                  e.printStackTrace();  
              }  
          }  
      }  
  }  
}