Struts Web 应用程序中的 JasperReport 错误

Question

我在基于 Struts 的 Web 应用程序中使用 JasperReport 以及 NetBeans 6.8 和 IReport 插件 3.7.4。我在操作类中收到以下错误：

java.lang.NullPointerException
    at java.io.ObjectInputStream$PeekInputStream.read(ObjectInputStream.java:2266)
    at java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2279)
    at java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:2750)
    at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:780)
    at java.io.ObjectInputStream.<init>(ObjectInputStream.java:280)
    at net.sf.jasperreports.engine.util.JRLoader.loadObject(JRLoader.java:188)
    at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:381)
    at net.sf.jasperreports.engine.JasperRunManager.runReportToPdfStream(JasperRunManager.java:186)
    at com.bspl.psys.ilp.action.ReportAppLinkAction.execute(ReportAppLinkAction.java:65)
    at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
    at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
    at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:734)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:332)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:233)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309)
    at java.lang.Thread.run(Thread.java:619)

我在操作类中使用了以下代码：

public ActionForward execute(ActionMapping mapping, ActionForm form,
            HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

         StringWriter stringWriter = new StringWriter();
         PrintWriter printWriter = new PrintWriter(stringWriter);
         ServletOutputStream servletOutputStream = response.getOutputStream();
         InputStream reportStream = getServlet().getServletConfig().getServletContext().getResourceAsStream("SampleReport.jasper");

         try {

            Class.forName("com.mysql.jdbc.Driver").newInstance();
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/SampleDB?user=common&password=common");

            JasperRunManager.runReportToPdfStream(reportStream, servletOutputStream,new HashMap());

            connection.close();
            response.setContentType("application/pdf");
            response.reset();
            reportStream.close();
            servletOutputStream.flush();
            servletOutputStream.close();

        }  catch (Exception ex) {

            ex.printStackTrace(printWriter);
            response.setContentType("text/plain");
            response.getOutputStream().print(stringWriter.toString());
        }

          return null;
    }

请建议我哪里出错了。我是第一次使用 JasperReport，束手无策:(

更新

我认为问题出在报告本身。即使是简单的代码也会出现错误：

try {
  Class.forName("com.mysql.jdbc.Driver").newInstance();
  connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/SampleDB?user=common&password=common);
  JasperFillManager.fillReportToFile("D:/dropbox/report/SampleReport.jasper",new HashMap(), connection);
  System.out.println("Done!");
} catch (Exception ex) {
  ex.printStackTrace(printWriter);
  response.setContentType("text/plain");
  response.getOutputStream().print(stringWriter.toString());
}
return null;
}

这次出现不同的错误消息：

java.lang.NullPointerException
at net.sf.jasperreports.engine.fill.JRFiller.fillReport(JRFiller.java:63)
at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:402)
at net.sf.jasperreports.engine.JasperFillManager.fillReportToFile(JasperFillManager.java:188)
at net.sf.jasperreports.engine.JasperFillManager.fillReportToFile(JasperFillManager.java:94)
at com.bspl.psys.ilp.action.ReportAppLinkAction.execute(ReportAppLinkAction.java:84)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:734)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97)
at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:332)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:233)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309)
at java.lang.Thread.run(Thread.java:619)

但是当我在 IReport 设计器中查看报表时，预览会正确显示，请帮助启动报表。

Answer 1

警告：我不是 struts 开发人员（更多的是 JSF 1.2/2.0）：

JasperReports 相当挑剔，而且错误信息非常冗长，除非您专门将其配置为静默运行。空指针异常通常来自您不期望的地方（图像/简单文本等...），不幸的是有时您会在“loadObject”或“fillReport”调用中收到很少或没有信息的错误。

尝试将其分解为一系列步骤，并在调试器中查看它以准确了解失败的位置。一旦你把它拆开，这可能是理所当然的。删除所有图像等...并运行空白报告（字面上是一个 hello world），以确保 NPE 不在报告内并且您的框架正常工作。一旦你把它分成几个部分，调试起来就会很容易。

通常你可以检查每个步骤：

//load == classloader (I'm inside JBoss so I have to explicitly define it)
//This is pseudo code pulled from my test environment

JasperReport report = JasperCompileManager.compileReport(load.getResourceAsStream("yourpackage/report.jrxml"));
JasperPrint print = JasperFillManager.fillReport(report, new Map<String, Object>(), java.sql.Connection);      
JasperExportManager.exportReportToPdfStream(print, outStream); 

我真的不建议在生产环境中编译（使用打印是最好的方法），但我遇到了一系列类加载问题（JBoss相关），由图像和其他细节引起的NPE以及报告中各种不良脚本引起的错误。

在框架内进行测试，您很快就会发现问题。 Jasper 可以说是最好的 Java 报告软件（非常详细），但调试起来却相当令人恼火。

通过将其分解为步骤，可以更轻松地调试并查看 NPE 实际存在的位置。您使用的代码似乎没问题：我会将钱放在空流或报告中未找到的资源（可能是图像）上。