使用JFreeChart构造统计图

public class ChartServlet extends HttpServlet
...{
    // 请求处理方法
    public void doPost( HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException 
    ...{
        // 得到用户的投票信息
        String id = request.getParameter( "id" );
        IVoteDAO dao = DAOFactory.getVoteDAO();
        Vote vote = dao.getVote( id );
        
        // 得到JFreeChart对象的实例
        JFreeChart chart = getChart( vote );
        // 设置输出对象的类型
        response.setContentType( "image/jpeg" );
        // 输出图形
        ChartUtilities.writeChartAsJPEG( response.getOutputStream(),
            100, chart, 400, 300, null);
    }
    
    // 请求处理方法
    public void doGet( HttpServletRequest request, HttpServletResponse response )
            throws ServletException, IOException
    ...{
        doPost( request, response );
    }

    // 得到JFreeChart对象的实例
    public static JFreeChart getChart( Vote vote )
    ...{
        JFreeChart chart = null;
        // 判断是否为饼图
        if( vote.getPictype().indexOf( "PIE" ) == 0 )
        ...{
            // 组织生成饼图的数据
            DefaultPieDataset data = new DefaultPieDataset();
            
            Iterator it = vote.getVoteitems().iterator();
            while( it.hasNext() )
            ...{
                VoteItem vi = (VoteItem)it.next();
                data.setValue( vi.getTitle(), vi.getVotenum() );
            }
            
            // 判断是否为普通饼图
            if( "PIE".equals( vote.getPictype() ) )
            ...{
                chart = ChartFactory.createPieChart( vote.getTitle(),
                        data, false, false, false );
            }
            else    // 3D饼图
            ...{
                chart = ChartFactory.createPieChart3D( vote.getTitle(),
                        data, false, false, false );
            }
        }
        else
        ...{
            // 组织柱状图的数据
            DefaultCategoryDataset data = new DefaultCategoryDataset();
            
            Iterator it = vote.getVoteitems().iterator();
            while( it.hasNext() )
            ...{
                VoteItem vi = (VoteItem)it.next();
                data.addValue( vi.getVotenum(), "选项", vi.getTitle() );
            }

            // 判断是否为普通柱状图
            if( "BAR".equals( vote.getPictype() ) )
            ...{
                chart = ChartFactory.createBarChart( vote.getTitle(),
                    "选项", "数量", data, PlotOrientation.VERTICAL,
                    false, false, false );
            }
            else    // 3D柱状图
            ...{
                chart = ChartFactory.createBarChart3D( vote.getTitle(),
                        "选项", "数量", data, PlotOrientation.VERTICAL,
                        false, false, false );
            }
        }
        return chart;
    }
}