java 关于数据库的连接并查询（二）

编写一个应用程序，连接SQL Server数据库Stu，并访问数据库中grade表，并可以通过课程号下拉表列选择课程号，并将表中的内容输出在窗口界面的表格中

public class Grade {
	public static void main(String args[]){
		String tableHead[];
		String content[][]; 
		JTable table ;
		JComboBox com=new JComboBox();
		com.addItem("all");
		com.addItem("C01");
		com.addItem("C02");
		com.addItem("C03");
		com.addItem("C04");
		com.addItem("C05");
		com.addItem("C06");
		JFrame win = new JFrame();
		Query findRecord = new  Query();
		findRecord.setDatabaseName("STU20200101");
		findRecord.setSQL("select * from GradeS");
		content = findRecord.getRecord();
		tableHead=findRecord.getColumnName();
		table = new JTable(content,tableHead); 
		DefaultTableModel model = new DefaultTableModel(content,tableHead);
        table.setModel(model);
		TableRowSorter sorter = new TableRowSorter(model);
		table.setRowSorter(sorter);
		com.addItemListener(new ItemListener() {
			public void itemStateChanged(ItemEvent e) {
				String s = com.getSelectedItem().toString();
				if(s=="all") {
					sorter.setRowFilter(RowFilter.regexFilter("."));
				}
				else if(s=="C01") {
					sorter.setRowFilter(RowFilter.regexFilter("C01"));
				}
				else if(s=="C02") {
					sorter.setRowFilter(RowFilter.regexFilter("C02"));
				}
				else if(s=="C03") {
					sorter.setRowFilter(RowFilter.regexFilter("C03"));
				}
				else if(s=="C04") {
					sorter.setRowFilter(RowFilter.regexFilter("C04"));
				}
				else if(s=="CO5") {
					sorter.setRowFilter(RowFilter.regexFilter("C05"));
				}
				else if(s=="C06") {
					sorter.setRowFilter(RowFilter.regexFilter("C06"));
				}
			}

		});	
		 win.add(com,BorderLayout.NORTH);
	        win.add(new JScrollPane(table),BorderLayout.CENTER);
	        win.setBounds(200,200,500,400);
			win.setVisible(true);
			win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			win.setTitle("数据库顺序查询");
	}
}

public class Query {
   String databaseName="";    	//数据库名
   String SQL;        		//SQL语句
   String columnName[];        //全部字段（列）名
   String record[][];          //查询到的记录
   public Query() {
      try{  Class.forName("com.mysql.jdbc.Driver");    //加载JDBC-MySQL驱动
      }
      catch(Exception e){}
   }
   public void setDatabaseName(String s) {
      databaseName=s.trim();
   }
   public void setSQL(String SQL) {
      this.SQL=SQL.trim();
   }
   public String[] getColumnName() {
       if(columnName ==null ){
           System.out.println("先查询记录");
           return null;
       }
       return columnName;
   }
   public String[][] getRecord() {
       startQuery();
       return record;
   }
   private void startQuery() { 
      Connection con;
      Statement sql;  
      ResultSet rs;
      String url = "jdbc:sqlserver://localhost:1433;DatabaseName=STU20200101";
      try { 
        con=DriverManager.getConnection(url,"sa","123456");
        sql=con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
                                ResultSet.CONCUR_READ_ONLY);
        rs=sql.executeQuery(SQL);
        ResultSetMetaData metaData = rs.getMetaData();
        int columnCount = metaData.getColumnCount();      //字段数目 
        columnName=new String[columnCount]; 
        for(int i=1;i<=columnCount;i++){
            columnName[i-1]=metaData.getColumnName(i);
        } 
        rs.last(); 
        int recordAmount =rs.getRow();     //结果集中的记录数目
        record = new String[recordAmount][columnCount];
        int i=0;
        rs.beforeFirst();
        while(rs.next()) { 
          for(int j=1;j<=columnCount;j++){
             record[i][j-1]=rs.getString(j);    //第i条记录，放入二维数组的第i行
          }
          i++;
        }
        con.close();
      }
      catch(SQLException e) {
        System.out.println("请输入正确的表名"+e);
      }
   }    
}

运行结果：