queryapplet.java

JAVA数据库编程实例源码及其一些Java基本介绍

package querydbinapplet;

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.sql.*;
import java.util.*;
import javax.swing.*;
import javax.swing.table.*;

/**
 * Title:			Applet与Servlet通讯查询数据库
 * Description:			教学示范
 * Copyright:			Copyright (c) 2003
 * Company:			北京师范大学计算机系
 * @author			孙一林
 * @version			1.0
 */

public class queryApplet extends Applet {
  private boolean isStandalone = false;
  private Button queryButton = new Button();
  private TextField queryTextField = new TextField();
  private Label queryLabel = new Label();

  String title[];                              //定义显示数据表格的标题
  Vector vector;                               //定义存储结果集数据的数组
  AbstractTableModel tm;                       //定义显示数据表格的抽象类
  JScrollPane scroll;                          //定义装载数据表格的容器
  boolean lastQuery = false;                   //上次查询是否成功

  public String getParameter(String key, String def) {
    return isStandalone ? System.getProperty(key, def) :
      (getParameter(key) != null ? getParameter(key) : def);
  }

  public queryApplet() {
  }

  public void init() {
    try {
      jbInit();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }

  private void jbInit() throws Exception {
    queryButton.setLabel("查询");
    queryButton.setBounds(new Rectangle(288, 348, 75, 29));
    queryButton.addActionListener(new java.awt.event.ActionListener() {
      public void actionPerformed(ActionEvent e) {
        queryButton_actionPerformed(e);
      }
    });
    this.setLayout(null);
    queryTextField.setBounds(new Rectangle(107, 26, 168, 26));
    queryLabel.setText("请输入学号");
    queryLabel.setBounds(new Rectangle(24, 26, 69, 21));
    this.add(queryLabel, null);
    this.add(queryTextField, null);
    this.add(queryButton, null);
  }

  public void start() {
  }

  public void stop() {
  }

  public void destroy() {
  }

  public String getAppletInfo() {
    return "Applet Information";
  }

  public String[][] getParameterInfo() {
    return null;
  }

  private void getResult() //把用户在applet中输入的查询学号传送给Servlet，然后把Servlet的处理结果显示出来

  {
    try
    {
      String Num = queryTextField.getText();           //获取要查询的学号
      URL servletURL = new URL(this.getDocumentBase(),"queryservlet");  //创建与后台Servlet通讯的连接实例
      URLConnection connection = servletURL.openConnection();    //与后台Servlet进行连接
      connection.setUseCaches(false);                         //设置连接不使用缓存
      connection.setDoOutput(true);                           //设置连接的Servlet进行输出
      ByteArrayOutputStream byteStream = new ByteArrayOutputStream(1024);  //创建二进制字节流ByteArrayOutputStream实例
      PrintWriter out = new PrintWriter(byteStream, true);    //创建向二进制字节流写入文本数据的PrintWriter实例
      String postData = "Num=" + URLEncoder.encode(Num);      //将学生学号以URL方式编码
      out.print(postData);                                    //将学生学号写入二进制字节流
      out.flush();                                            //清空PrintWriter
      String lengthString = String.valueOf(byteStream.size());    //获取学生学号长度，即向Servlet传送的参数的长度
      connection.setRequestProperty("Content-Length", lengthString);  //设置与Servlet的连接的输入参数长度
      connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");//把与Servlet连接的输入参数转化为x-www-form-urlencoded格式
      byteStream.writeTo(connection.getOutputStream());       //将学生学号传送到后台Servlet进行查询
      BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));  //创建读取Servlet处理结果的BufferReader实例
      String resultStr = br.readLine();               //读取后台Servlet以字符串形式返回的查询结果
      displayResult(resultStr);                       //处理查询结果字符串获取查询结果并显示
    }
    catch(Exception ex)
    {
      ex.printStackTrace();
    }
  }

  void displayResult(String resultStr)                //处理查询结果字符串获取查询结果并以表格方式显示
  {
    int colCount = Integer.parseInt(trimColCount(resultStr));      //解析查询结果字符串获取查询结果的字段数
    int recordCount = Integer.parseInt(trimRecordCount(resultStr));  //解析查询结果字符串获取查询结果的记录数
    if (recordCount==0)               //若查询结果为空，则返回查询结果为空的信息
    {
      JOptionPane msg = new JOptionPane();
      JOptionPane.showMessageDialog(this, "数据库中没有您查询的学号", "数据库中没有您查询的学号！", 1);
      lastQuery = false;                              //数据库查询操作失败
    }
    else                              //若查询结果不为空，则创建表格显示查询数据
    {
      String[][] result = new String[recordCount+1][colCount];  //创建存取查询结果的二维字符串数组
      result = trimResult(colCount, recordCount, resultStr);    //解析查询结果字符串获取查询结果的各个字段存入查询结果数组中
      title = new String[colCount];                             //获取显示数据的表格的标题
      for(int i=0; i<colCount; i++)
      {
        title[i] = new String(result[0][i]);
      }
      initTable();                                             //初始化显示数据的表格
      vector.removeAllElements();                              //刷新表格并显示查询结果数组中的结果
      tm.fireTableStructureChanged();
      for(int i=1; i<=recordCount; i++)
      {
        Vector rec_vector = new Vector();
        for(int j=0; j<colCount; j++)
        {
          rec_vector.addElement(result[i][j]);
        }
        vector.addElement(rec_vector);
      }
      tm.fireTableStructureChanged();
      lastQuery = true;                              //数据库查询操作成功
    }
  }

  String trimColCount(String s)                   //解析查询结果字符串获取查询结果的字段数
  {
    int idx = s.indexOf('#');
    return s.substring(0,idx);
  }

  String trimRecordCount(String s)                //解析查询结果字符串获取查询结果的记录数
  {
    int idx1 = s.indexOf('#');
    int idx2 = s.indexOf('#',idx1+1);
    return s.substring(idx1+1,idx2);
  }

  String[][] trimResult(int colCount, int recordCount, String s)    //解析查询结果字符串获取查询结果的各个字段
  {
    String[][] result = new String[recordCount+1][colCount];
    int idx1 = s.indexOf('#');
    int idx2 = s.indexOf('#',idx1+1);
    int idx3;
    for(int i=0; i<=recordCount; i++)
    {
      for(int j=0; j<colCount; j++)
      {
        idx3 = s.indexOf('#', idx2+1);
        result[i][j] = s.substring(idx2+1, idx3);
        idx2 = idx3;
      }
    }
    return result;
  }

  void initTable() {                           //初始化显示数据集结果的表格
    JTable table;
    vector = new Vector();
    tm = new AbstractTableModel() {            //实现表格抽象类的接口
      public int getColumnCount() {
        return title.length;
      }
      public int getRowCount() {
        return vector.size();
      }
      public Object getValueAt(int row, int column) {
        if(!vector.isEmpty())
        {
          return ((Vector)vector.elementAt(row)).elementAt(column);
        }
        else
        {
          return null;
        }
      }
      public void setValueAt(Object value, int row, int column)
      {

      }
      public String getColumnName(int column)
      {
        return title[column];
      }
      public Class getColumnClass(int c)
      {
        return getValueAt(0,c).getClass();
      }
      public boolean isCellEditable(int row, int column)
      {
        return false;
      }
    };
    table = new JTable(tm);
    table.setToolTipText("Display Query Result");
    table.setAutoResizeMode(table.AUTO_RESIZE_SUBSEQUENT_COLUMNS);
    table.setCellSelectionEnabled(false);
    table.setShowHorizontalLines(true);
    table.setShowVerticalLines(true);
    scroll = new JScrollPane(table);
    scroll.setBounds(20,60,550,200);
    this.add(scroll,null);
  }

  public static void main(String[] args) {
    queryApplet applet = new queryApplet();
    applet.isStandalone = true;
    Frame frame;
    frame = new Frame() {
      protected void processWindowEvent(WindowEvent e) {
        super.processWindowEvent(e);
        if (e.getID() == WindowEvent.WINDOW_CLOSING) {
          System.exit(0);
        }
      }
      public synchronized void setTitle(String title) {
        super.setTitle(title);
        enableEvents(AWTEvent.WINDOW_EVENT_MASK);
      }
    };
    frame.setTitle("Applet Frame");
    frame.add(applet, BorderLayout.CENTER);
    applet.init();
    applet.start();
    frame.setSize(400,320);
    Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
    frame.setLocation((d.width - frame.getSize().width) / 2, (d.height - frame.getSize().height) / 2);
    frame.setVisible(true);
  }

  void queryButton_actionPerformed(ActionEvent e) {  //把用户在applet中输入的查询学号传送给Servlet，然后把Servlet的处理结果使用表格显示
    if(lastQuery==true)                               //若上次查询成功，则首先清除上次查询的表格
    {
      scroll.setVisible(false);
      this.remove(scroll);
    }
    getResult();                                    //处理输入的查询学号并传送给Servlet，然后把Servlet的处理结果使用表格显示
  }
}