ClassCastException occurs but without any proper details

Question

I'm using Dynamic Reports which in turn uses Jasper Reports for generating a pdf. I'm getting a ClassCastException in my code by I can't understand anything from it. If anyone understand where exactly might be the error, please help me. Sorry if I miss any details as I'm in a hurry to go. Feel free to ask any extra details needed.

This is the code where error occurs

public void createPdf(OutputStream out) {
    SubreportBuilder subreport = cmp.subreport(new SubreportExpression())
            .setDataSource(new SubreportDataSourceExpression());

    JasperPdfExporterBuilder pdfExporter = Exporters.pdfExporter("D:\\PDF\\report.pdf");
    try {
        report()
                .detail(
                subreport,
                cmp.verticalGap(20))
                .pageHeader(PdfTemplate.headerPortraitComponent)
                .pageFooter(PdfTemplate.footerPortraitComponent)
                .setDataSource(createDataSource())
                .toPdf(out);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

This is the error output

Jun 28, 2013 5:09:32 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [CMCaseServlet] in context with path [] threw exception
net.sf.jasperreports.engine.JRRuntimeException: net.sf.jasperreports.engine.fill.JRExpressionEvalException: Error evaluating expression : 
    Source text : $F{column1}
    at net.sf.jasperreports.engine.fill.JRFillSubreport.prepare(JRFillSubreport.java:782)
    at net.sf.jasperreports.engine.fill.JRFillElementContainer.prepareElements(JRFillElementContainer.java:331)
    at net.sf.jasperreports.engine.fill.JRFillBand.fill(JRFillBand.java:384)
    at net.sf.jasperreports.engine.fill.JRFillBand.fill(JRFillBand.java:358)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillColumnBand(JRVerticalFiller.java:2046)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillDetail(JRVerticalFiller.java:778)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportContent(JRVerticalFiller.java:308)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:155)
    at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:909)
    at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:841)
    at net.sf.jasperreports.engine.fill.JRFiller.fill(JRFiller.java:88)
    at net.sf.jasperreports.engine.JasperFillManager.fill(JasperFillManager.java:653)
    at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:969)
    at net.sf.dynamicreports.jasper.builder.JasperReportBuilder.toJasperPrint(JasperReportBuilder.java:308)
    at net.sf.dynamicreports.jasper.builder.JasperReportBuilder.show(JasperReportBuilder.java:327)
    at cliff.reports.CMCaseReport.createPdf(CMCaseReport.java:58)
    at cliff.servlet.CMCaseServlet.processRequest(CMCaseServlet.java:366)
    at cliff.servlet.CMCaseServlet.doGet(CMCaseServlet.java:611)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at cliff.filter.LoginFilter.doFilter(LoginFilter.java:37)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1812)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Caused by: net.sf.jasperreports.engine.fill.JRExpressionEvalException: Error evaluating expression : 
    Source text : $F{column1}
    at net.sf.jasperreports.engine.fill.JREvaluator.evaluate(JREvaluator.java:203)
    at net.sf.jasperreports.engine.fill.JRCalculator.evaluate(JRCalculator.java:591)
    at net.sf.jasperreports.engine.fill.JRCalculator.evaluate(JRCalculator.java:559)
    at net.sf.jasperreports.engine.fill.JRFillElement.evaluateExpression(JRFillElement.java:966)
    at net.sf.jasperreports.engine.fill.JRFillTextField.evaluateText(JRFillTextField.java:456)
    at net.sf.jasperreports.engine.fill.JRFillTextField.evaluate(JRFillTextField.java:440)
    at net.sf.jasperreports.engine.fill.JRFillElementContainer.evaluate(JRFillElementContainer.java:259)
    at net.sf.jasperreports.engine.fill.JRFillFrame.evaluate(JRFillFrame.java:149)
    at net.sf.jasperreports.engine.fill.JRFillElementContainer.evaluate(JRFillElementContainer.java:259)
    at net.sf.jasperreports.engine.fill.JRFillBand.evaluate(JRFillBand.java:455)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillColumnBand(JRVerticalFiller.java:2044)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillDetail(JRVerticalFiller.java:778)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportStart(JRVerticalFiller.java:288)
    at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:151)
    at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:909)
    at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:841)
    at net.sf.jasperreports.engine.fill.JRFillSubreport.fillSubreport(JRFillSubreport.java:655)
    at net.sf.jasperreports.engine.fill.JRSubreportRunnable.run(JRSubreportRunnable.java:59)
    at net.sf.jasperreports.engine.fill.AbstractThreadSubreportRunner.run(AbstractThreadSubreportRunner.java:203)
    ... 3 more
Caused by: java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
    at Report_1372410572739_904220.evaluate(Report_1372410572739_904220:202)
    at net.sf.jasperreports.engine.fill.JREvaluator.evaluate(JREvaluator.java:190)
    ... 21 more

UPDATE

code for other methods

private static JRDataSource createDataSource() {
    return new JREmptyDataSource(7);
}

private class SubreportExpression extends AbstractSimpleExpression<JasperReportBuilder> {

    private static final long serialVersionUID = 1L;

    @Override
    public JasperReportBuilder evaluate(ReportParameters reportParameters) {
        int masterRowNumber = reportParameters.getReportRowNumber();
        JasperReportBuilder report = null;
        try {
            switch (masterRowNumber) {
                case 1:
                    report = getCaseReport();
                    break;
                case 2:
                    report = getRequestsReport();
                    break;
                case 3:
                    report = getObjectiveReport();
                    break;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return report;
    }
}

private class SubreportDataSourceExpression extends AbstractSimpleExpression<JRDataSource> {

    private static final long serialVersionUID = 1L;

    @Override
    public JRDataSource evaluate(ReportParameters reportParameters) {
        int masterRowNumber = reportParameters.getReportRowNumber();
        DRDataSource dataSource = null;
        try {

            switch (masterRowNumber) {
                case 1:
                    dataSource = getCaseDS();
                    break;
                case 2:
                    dataSource = getRequestsDS();
                    break;
                case 3:
                    dataSource = getObjectiveDS();
                    break;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

        return dataSource;
    }
}

private JasperReportBuilder getCaseReport() {
    JasperReportBuilder report = report();
    try {
        report
                .setTemplate(PdfTemplate.reportTemplate2)
                .title(cmp.text("CM Details").setStyle(PdfTemplate.bold12LeftStyle));

        for (int i = 1; i <= 4; i++) {
            report.addColumn(col.column("", "column" + i, type.stringType()));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return report;
}



private DRDataSource getCaseDS() {
    String[] columns = new String[4];
    for (int i = 0; i < 4; i++) {
        columns[i] = "column" + (i + 1);
    }
    DRDataSource dataSource = new DRDataSource(columns);

    try {
        if (c== null) {  // c is a instance variable initiated by constructor
            c= new CMCase();
        }

        Object[] values = new Object[4];

        values[0] = "ID";
        values[1] = c.getOd(); // String
        values[2] = "Person In Charge";
        values[3] = c.getPicId();
        dataSource.add(values);

        values[0] = "Customer ID";
        values[1] = c.getCustomerId();  // String
        values[2] = "Assign Date";
        values[3] = c.getAssignDate(); // date already parsed to String from class
        dataSource.add(values);

        values[0] = "Account Number";
        values[1] = c.getAccountNumber(); // String
        values[2] = "Counter";
        values[3] = Integer.toString(c.getCounter());  // int parsed to String
        dataSource.add(values);

    } catch (Exception e) {
        e.printStackTrace();
    }
    return dataSource;
}

while in debugging mode, error occurs in when masterRowNumber is 1 itself so remaining methods not given

Answer 1

The given exception is quite clear

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

The JVM is expecting a java.lang.String and you give it a java.lang.Integer. An Integer cannot be cast to a String.

This must be something with either your template or your data given to the template.

Answer 2

The exception says: Jasper expects somewhere in your datasource an int, but you gave it a String.
Maybe you have to check the data you give into the report.

Answer 3

Field or parameter in template expects object of defined type. You may have trouble to find which one causes the problem. This is a way how I track it down in Eclipse:

1. create Java Exception Breakpoint for ClassCastException (e.g. by clicking on the exception class in the Console)
2. when the debugger stops, try to go up the call stack in the Debug view, until you find "expression" variable in the Variables view.
3. and it until you find the variable or property name in trouble
4. find it in iReport and fix the "Field class" or "Parameter class"

Or alternatively, search for the "to" class in the jrxml file, maybe there are not many of them. In case of "A cannot be cast to B" search for B.