连接到数据库的程序的源代码

这个程序是连接到数据库的一个程序，主要功能是在上方的文本输入框中输入查询语句，实现从数据库中查询的功能，还可以在下方的过滤文本框中输入要过滤的文本，实现过滤查询结果的功能。

现在的问题是编译能够成功，但是运行时会报错。错误信息及源代码在下面给出，请问原因为何？多谢指教。

//这是ResultSetTableModel类，用作JTable的构造函数的参数。

package ResultSetTableModel;

import java.sql.*;

import javax.swing.table.*;

public class ResultSetTableModel extends AbstractTableModel

{

private Connection connection;

private Statement statement;

private ResultSet resultset;

private ResultSetMetaData metadata;

private int numberofrows;

private boolean connectedtodatabase=false;

public ResultSetTableModel(String url,String username,String password,String query) {

try

{

connection=DriverManager.getConnection(url,username,password);

statement=connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet .CONCUR_READ_ONL Y);

connectedtodatabase=true;

setQuery(query);

}

catch(SQLException sqlexception)

{

System.out.println("error on connecting to database");

}

}

public void setQuery(String query) throws SQLException,IllegalStateException {

if(!connectedtodatabase)

{

throw new IllegalStateException("Not connected to database");

}

resultset=statement.executeQuery(query);

metadata=resultset.getMetaData();

}

public void disconnectFromDatabase()

{

if(connectedtodatabase)

{

try

{

resultset.close();

statement.close();

connection.close();

}

catch(SQLException sqlException)

{

sqlException.printStackTrace();

}

finally

{

connectedtodatabase=false;

}

}

}

public int getColumnCount() throws IllegalStateException

{

int currentrow=1;

if(!connectedtodatabase)

{

throw new IllegalStateException("Not connected to database");

}

try

{

https://www.360docs.net/doc/5d10278984.html,st();

currentrow=resultset.getRow();

}

catch(SQLException sqlexception)

{

sqlexception.printStackTrace();

}

return currentrow;

}

public Class getColumnClass(int column) throws IllegalStateException {

if(!connectedtodatabase)

{

throw new IllegalStateException("Not connected to database");

}

try

{

String className=metadata.getColumnClassName(column+1);

return Class.forName(className);

}

catch(Exception exception)

{

exception.printStackTrace();

}

finally

{

return Object.class;

}

}

public String getColumnName(int column) throws IllegalStateException {

String columnname="null";

if(!connectedtodatabase)

{

throw new IllegalStateException("Not connected to database");

}

try

{

columnname=metadata.getColumnName(column+1);

}

catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

finally

{

return columnname;

}

}

public int getRowCount() throws IllegalStateException

{

int rowcount=0;

if(!connectedtodatabase)

{

throw new IllegalStateException("Not connected to database");

}

try

{

https://www.360docs.net/doc/5d10278984.html,st();

rowcount=numberofrows=resultset.getRow();

}

catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

finally

{

return numberofrows;

}

}

public String getValueAt(int row,int column) throws IllegalStateException {

if(!connectedtodatabase)

{

throw new IllegalStateException("Not connected to database");

}

try

{

resultset.absolute(row+1);

return resultset.getObject(column+1).toString();

}

catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

return "";

}

}

//这是QueryData类，其中实现了图形界面

package ResultSetTableModel;

import java.awt.*;

import javax.swing.*;

import java.awt.event.*;

import java.sql.SQLException;

import java.util.regex.*;

import javax.swing.table.*;

public class QueryData extends JFrame

{

static final String DATABASEURL="jdbc:oracle:thin:@localhost:1521:orcl";

static final String DATABASEUSERNAME="scott";

static final String DATABASEPASSWORD="123456";

private JButton submitquery;

private Box boxnorth,boxsouth;

private JTextArea inquerysentence;

private JTextField filtercondition;

private JButton applyfilter;

private ResultSetTableModel tablemodel;

private JTable resulttable;

public QueryData()

{

super("Displaying query results");

Box boxnorth,boxsouth;

JTextArea inquerysentence;

JTextField filtercondition;

JButton applyfilter;

ResultSetTableModel tablemodel=new ResultSetTableModel(DA TABASEURL,DATABASEUSERNAME,DATABASEPASSWORD,"sel ect * from emp");

boxnorth=Box.createHorizontalBox();

boxsouth=Box.createHorizontalBox();

inquerysentence=new JTextArea("select * from emp",30,100);

inquerysentence.setWrapStyleWord(true);

inquerysentence.setLineWrap(true);

submitquery=new JButton("Submit Query");

boxnorth.add(new JScrollPane(inquerysentence));

boxnorth.add(submitquery);

JTable resulttable=new JTable(tablemodel);

JLabel filterflag=new JLabel("Filter");

filtercondition=new JTextField();

applyfilter=new JButton("Apply Filter");

boxsouth.add(filterflag);

boxsouth.add(filtercondition);

boxsouth.add(applyfilter);

add(boxnorth,BorderLayout.NORTH);

add(new JScrollPane(resulttable),BorderLayout.CENTER);

add(boxsouth,BorderLayout.SOUTH);

setSize(500,500);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

submitQuery(inquerysentence.getText());

applyFilter(filtercondition.getText());

}

public void submitQuery(final String sentencetoinquery)

{

submitquery.addActionListener(

new ActionListener()

{

public void actionPerformed(ActionEvent actionevent)

{

try

{

tablemodel.setQuery(sentencetoinquery);

}

catch(SQLException sqlexception)

{

JOptionPane.showMessageDialog(null,

sqlexception.getMessage(),"Database error",

JOptionPane.ERROR_MESSAGE

);

}

}

}

);

}

public void applyFilter(final String filtercondition)

{

final TableRowSorter sorter=new TableRowSorter(tablemodel);

resulttable.setRowSorter(sorter);

applyfilter.addActionListener(

new ActionListener()

{

public void actionPerformed(ActionEvent actionevent)

{

if(filtercondition.length()==0)

{

sorter.setRowFilter(null);

}

else

{

try

{

sorter.setRowFilter(RowFilter.regexFilter(filtercondition));

}

catch(Exception exception)

{

JOptionPane.showMessageDialog(null,

"Bad regex pattern","Bad regex pattern",

JOptionPane.ERROR_MESSAGE

);

}

}

}

}

);

}

public static void main(String[] args) {

new QueryData();

}

}

//下面是运行时的错误信息

error on connecting to database

Exception in thread "main" https://www.360docs.net/doc/5d10278984.html,ng.IllegalStateException: Not connected to database

at

ResultSetTableModel.ResultSetTableModel.getColumnCount(ResultSetTableModel. java:64)

at javax.swing.JTable.createDefaultColumnsFromModel(JTable.java:1287)

at javax.swing.JTable.tableChanged(JTable.java:4386)

at javax.swing.JTable.setModel(JTable.java:3688)

at javax.swing.JTable.(JTable.java:634)

at javax.swing.JTable.(JTable.java:575)

at ResultSetTableModel.QueryData.(QueryData.java:41)

at ResultSetTableModel.QueryData.main(QueryData.java:117)