示例1：通过本地文件导入导出数据

在使用JAVA语言基于openGauss进行二次开发时，可以使用CopyManager接口，通过流方式，将数据库中的数据导出到本地文件或者将本地文件导入数据库中，文件格式支持CSV、TEXT等格式。

样例程序如下，执行时需要加载openGauss的JDBC驱动。

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.opengauss.copy.CopyManager;
import org.opengauss.core.BaseConnection;

public class Copy{

     public static void main(String[] args)
     {
      String urls = new String("jdbc:opengauss://localhost:8000/postgres"); //数据库URL
      String username = new String("username");            //用户名
      String password = new String("passwd");             //密码
      String tablename = new String("migration_table"); //定义表信息
      String tablename1 = new String("migration_table_1"); //定义表信息
      String driver = "org.opengauss.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);
      }

      // 将表migration_table中数据导出到本地文件d:/data.txt
      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();
      }
      //将d:/data.txt中的数据导入到migration_table_1中。
      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();
      }

      // 将表migration_table_1中的数据导出到本地文件d:/data1.txt
      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();
              }
          }
      }
  }
}