Question

早上好！我有一个方法＆＃34; gerarJasper＆＃34;使用JasperReports打印报告。此方法将列表作为参数，因此我可以在整个应用程序中使用此方法。但是，当此列表不包含任何数据时，JasperReports将打印一个空白PDF。我想做什么：当data参数为空时，我想在此列表中添加一个对象。我有如何在运行时找到List的Object类型

下面的代码

public void imprimir(List<TrUltimaLocalizacaoGps> l){
    try {           
        super.gerarJasper("RelLstTrUltimaLocalizacaoGps", "PDF", l, new HashMap());
    } catch (Exception e) {         
        e.printStackTrace();
    }
}

public void gerarJasper(String jasperName, String type, List data, Map params) throws IllegalArgumentException, RuntimeException, Exception {

    boolean found = false;
    for (int i = 0; i < VALID_TYPES.length; i++) {
        if (VALID_TYPES[i].equals(type)) {
            found = true;
            break;
        }
    }
    if (!found) {
        throw new IllegalArgumentException("Tipo solicitado '" + type + "' inválido");
    }

    ExternalContext econtext = FacesContext.getCurrentInstance().getExternalContext();        
    InputStream stream = econtext.getResourceAsStream(PREFIX + name + SUFFIX);
    if (stream == null) {
        throw new IllegalArgumentException("O relatório '" + name + "' não existe");
    }

    FacesContext fc = FacesContext.getCurrentInstance();
    ServletContext context = (ServletContext)fc.getExternalContext().getContext();
    String path = context.getRealPath(File.separator) + "resources/jasper" + File.separator;
    params.put("SUBREPORT_DIR", path);

    // here I would like to know what the Object Type of the data parameter        
    JRDataSource ds = new JRBeanArrayDataSource(data.toArray());
    JasperPrint jasperPrint = null;
    try {
        jasperPrint = JasperFillManager.fillReport(stream, params, ds);
    } catch (RuntimeException e) {
        throw e;
    } catch (Exception e) {
        throw new FacesException(e);
    } finally {
        try {
            stream.close();
        } catch (IOException e) {
        }
    }

    JRExporter exporter = null;
    HttpServletResponse response = (HttpServletResponse) econtext.getResponse();
    FacesContext fcontext = FacesContext.getCurrentInstance();
    try {
        response.setContentType(type);
        if ("application/pdf".equals(type)) {
            exporter = new JRPdfExporter();
            exporter.setParameter(JRExporterParameter.JASPER_PRINT, jasperPrint);
            exporter.setParameter(JRExporterParameter.OUTPUT_STREAM, response.getOutputStream());
        } else if ("text/html".equals(type)) {
            exporter = new JRHtmlExporter();
            exporter.setParameter(JRExporterParameter.JASPER_PRINT, jasperPrint);
            exporter.setParameter(JRExporterParameter.OUTPUT_WRITER, response.getWriter());                
            HttpServletRequest request = (HttpServletRequest) fcontext.getExternalContext().getRequest();
            request.getSession().setAttribute(ImageServlet.DEFAULT_JASPER_PRINT_SESSION_ATTRIBUTE, jasperPrint);
            exporter.setParameter(JRHtmlExporterParameter.IMAGES_MAP, new HashMap());                
            exporter.setParameter(JRHtmlExporterParameter.IMAGES_URI, request.getContextPath() + "/image?image=");
        }
    } catch (RuntimeException e) {
        throw e;
    } catch (Exception e) {
        throw new FacesException(e);
    }

    try {
        exporter.exportReport();
    } catch (RuntimeException e) {
        throw e;
    } catch (Exception e) {
        throw new FacesException(e);
    }
    fcontext.responseComplete();
}

Answer 1

正如已经评论的那样，java的类型擦除使得无法找出什么类型的列表＆＃34;数据＆＃34;是。因此，您必须考虑替代问题。

一个选项是，，因为列表为空，它的类型真的很重要吗？如果没有，您可以在输入为空时创建一个包含一个项目的新列表：

JRDataSource ds = new JRBeanArrayDataSource(data.isEmpty() ? Arrays.asList(new SomeObject()), data.toArray());

另一个选项是，如果列表类型有所不同，您可以将其类作为参数传递：

public void gerarJasper(String jasperName, String type, List data, Map params, Class<?> listClass) throws IllegalArgumentException, RuntimeException, Exception {

然后在＆＃34;数据＆＃34;时创建一个新对象。是空的：

JRDataSource ds;
if (data.isEmpty()) {
    Constructor<?> ctor = clazz.getConstructor(String.class);
    Object object = ctor.newInstance();
    ds = new JRBeanArrayDataSource(object);
} else {
    ds = new JRBeanArrayDataSource(data.toArray());
}

最后，而不是在生成报告时向列表中添加内容，为什么不在创建时确保列表中始终存在某些内容。您可能知道创建它时的列表类型。根据应用程序的设置方式，这可能有意义。

列表中的对象类型

1 个答案: