basic.java

关系型数据库 Postgresql 6.5.2

package example;

import java.io.*;
import java.sql.*;
import java.text.*;

/**
 * This example tests the basic components of the JDBC driver, and shows
 * how even the simplest of queries can be implemented.
 *
 * To use this example, you need a database to be in existence. This example
 * will create a table called basic.
 *
 */

public class basic
{
  Connection db;	// The connection to the database
  Statement  st;	// Our statement to run queries with
  
  public basic(String args[]) throws ClassNotFoundException, FileNotFoundException, IOException, SQLException
  {
    String url = args[0];
    String usr = args[1];
    String pwd = args[2];
    
    // Load the driver
    Class.forName("postgresql.Driver");
    
    // Connect to database
    System.out.println("Connecting to Database URL = " + url);
    db = DriverManager.getConnection(url, usr, pwd);
    
    System.out.println("Connected...Now creating a statement");
    st = db.createStatement();
    
    // Clean up the database (in case we failed earlier) then initialise
    cleanup();
    
    // Now run tests using JDBC methods
    doexample();
    
    // Clean up the database
    cleanup();
    
    // Finally close the database
    System.out.println("Now closing the connection");
    st.close();
    db.close();
    
    //throw postgresql.Driver.notImplemented();
  }
  
  /**
   * This drops the table (if it existed). No errors are reported.
   */
  public void cleanup()
  {
    try {
      st.executeUpdate("drop table basic");
    } catch(Exception ex) {
      // We ignore any errors here
    }
  }
  
  /**
   * This performs the example
   */
  public void doexample() throws SQLException
  {
    System.out.println("\nRunning tests:");
    
    // First we need a table to store data in
    st.executeUpdate("create table basic (a int2, b int2)");
    
    // Now insert some data, using the Statement
    st.executeUpdate("insert into basic values (1,1)");
    st.executeUpdate("insert into basic values (2,1)");
    st.executeUpdate("insert into basic values (3,1)");
    
    // Now change the value of b from 1 to 8
    st.executeUpdate("update basic set b=8");
    System.out.println("Updated "+st.getUpdateCount()+" rows");
    
    // For large inserts, a PreparedStatement is more efficient, because it
    // supports the idea of precompiling the SQL statement, and to store
    // directly, a Java object into any column. PostgreSQL doesnt support
    // precompiling, but does support setting a column to the value of a
    // Java object (like Date, String, etc).
    //
    // Also, this is the only way of writing dates in a datestyle independent
    // manner. (DateStyles are PostgreSQL's way of handling different methods
    // of representing dates in the Date data type.)
    PreparedStatement ps = db.prepareStatement("insert into basic values (?,?)");
    for(int i=2;i<5;i++) {
      ps.setInt(1,4);		// "column a" = 5
      ps.setInt(2,i);		// "column b" = i
      ps.executeUpdate();	// executeUpdate because insert returns no data
    }
    ps.close();			// Always close when we are done with it
    
    // Finally perform a query on the table
    System.out.println("performing a query");
    ResultSet rs = st.executeQuery("select a, b from basic");
    if(rs!=null) {
      // Now we run through the result set, printing out the result.
      // Note, we must call .next() before attempting to read any results
      while(rs.next()) {
	int a = rs.getInt("a");	// This shows how to get the value by name
	int b = rs.getInt(2);	// This shows how to get the value by column
	System.out.println("  a="+a+" b="+b);
      }
      rs.close();	// again, you must close the result when done
    }
    
    // Now run the query again, showing a more efficient way of getting the
    // result if you don't know what column number a value is in
    System.out.println("performing another query");
    rs = st.executeQuery("select * from basic where b>1");
    if(rs!=null) {
      // First find out the column numbers.
      //
      // It's best to do this here, as calling the methods with the column
      // numbers actually performs this call each time they are called. This
      // really speeds things up on large queries.
      //
      int col_a = rs.findColumn("a");
      int col_b = rs.findColumn("b");
      
      // Now we run through the result set, printing out the result.
      // Again, we must call .next() before attempting to read any results
      while(rs.next()) {
	int a = rs.getInt(col_a); // This shows how to get the value by name
	int b = rs.getInt(col_b); // This shows how to get the value by column
	System.out.println("  a="+a+" b="+b);
      }
      rs.close();	// again, you must close the result when done
    }
    
    // The last thing to do is to drop the table. This is done in the
    // cleanup() method.
  }
  
  /**
   * Display some instructions on how to run the example
   */
  public static void instructions()
  {
    System.out.println("\nThis example tests the basic components of the JDBC driver, demonstrating\nhow to build simple queries in java.\n");
    System.out.println("Useage:\n java example.basic jdbc:postgresql:database user password [debug]\n\nThe debug field can be anything. It's presence will enable DriverManager's\ndebug trace. Unless you want to see screens of items, don't put anything in\nhere.");
    System.exit(1);
  }
  
  /**
   * This little lot starts the test
   */
  public static void main(String args[])
  {
    System.out.println("PostgreSQL basic test v6.3 rev 1\n");
    
    if(args.length<3)
      instructions();
    
    // This line outputs debug information to stderr. To enable this, simply
    // add an extra parameter to the command line
    if(args.length>3)
      DriverManager.setLogStream(System.err);
    
    // Now run the tests
    try {
      basic test = new basic(args);
    } catch(Exception ex) {
      System.err.println("Exception caught.\n"+ex);
      ex.printStackTrace();
    }
  }
}