Jasper Report的一个问题

Question

我被JasperReports困住了。我使用iReport开发了报告。当我在iReport中运行报表时，它运行得很好。但是当我在我的应用程序中通过servlet调用报告时，对于第一次调用，它工作正常。如果我第二次调用报告，则显示为＆＃34;文档没有页面＆＃34;即使我的数据库有所需的数据。再次，如果我重新启动我的tomcat服务器并调用相同的报告，它再次正常工作。当我再打一次电话时报告问题。谁能在这帮助我？

public class Repor extends JFrame {

    HashMap hm = null;
    Connection con = null;
    String reportName;

    public Repor() {
        setExtendedState(MAXIMIZED_BOTH);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    }

    public Repor(HashMap map) {
        this.hm = map;
        setExtendedState(MAXIMIZED_BOTH);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    }

    public Repor(HashMap map, Connection con) {
        this.hm = map;
        this.con = con;
        setExtendedState(MAXIMIZED_BOTH);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        setTitle("Report Viewer");
    }

    public void setReportName(String rptName) {
        this.reportName = rptName;
    }

    public void callReport() {
        JasperPrint jasperPrint = generateReport();
        JRViewer viewer = new JRViewer(jasperPrint);
        Container c = getContentPane();
        c.add(viewer);
        this.setVisible(true);
    }

    public void callConnectionLessReport() {
        JasperPrint jasperPrint = generateEmptyDataSourceReport();
        JRViewer viewer = new JRViewer(jasperPrint);
        Container c = getContentPane();
        c.add(viewer);
        this.setVisible(true);
    }

    public void closeReport() {
    }

    /** this method will call the report from data source*/
    public JasperPrint generateReport() {
        try {
            if (con == null) {
                try {
                    con = Database.getConnection();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
            JasperPrint jasperPrint = null;
            if (hm == null) {
                hm = new HashMap();
            }
            try {
                /**You can also test this line if you want to display 
                 * report from any absolute path other than the project root path*/
                jasperPrint = JasperFillManager.fillReport(reportName , hm, con);
            } catch (JRException e) {
                e.printStackTrace();
            }
            return jasperPrint;
        } catch (Exception ex) {
            ex.printStackTrace();
            return null;
        }
    }

    /** call this method when your report has an empty data source*/
    public JasperPrint generateEmptyDataSourceReport() {
        try {
            JasperPrint jasperPrint = null;
            if (hm == null) {
                hm = new HashMap();
            }
            try {
                jasperPrint = JasperFillManager.fillReport(reportName + ".jasper", hm, new JREmptyDataSource());
            } catch (JRException e) {
                e.printStackTrace();
            }
            return jasperPrint;
        } catch (Exception ex) {
            ex.printStackTrace();
            return null;
        }
    }
}