我是Java的新手，我遇到了无法解决的问题。我继承了这个项目，并且在我的一个脚本中包含以下代码：
DefaultLogger.logMessage("DEBUG path: "+ reportFile.getPath());
DefaultLogger.logMessage("DEBUG parameters: "+ parameters);
DefaultLogger.logMessage("DEBUG jr: "+ jr);
bytes = JasperRunManager.runReportToPdf(reportFile.getPath(), parameters, jr);
而且我得到以下结果（第四行在FootwearReportsServlet.doGet中有第287行）：
DEBUG path: C:\Development\JavaWorkspaces\Workspace1\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\RSLDevelopmentStandard\reports\templates\footwear\RslFootwearReport.jasper
DEBUG parameters: {class_list_subreport=net.sf.jasperreports.engine.JasperReport@b07af1, signature_path=images/logo_reports.jpg, submission_id=20070213154168780, test_results_subreport=net.sf.jasperreports.engine.JasperReport@5795ce, logo_path=images/logos_3.gif, report_connection_secondary=com.mysql.jdbc.JDBC4Connection@2c39d2, testing_packages_subreport=net.sf.jasperreports.engine.JasperReport@1883d5f, signature_path2=images/logo_reports.jpg, tpid_subreport=net.sf.jasperreports.engine.JasperReport@17531fd, first_page_subreport=net.sf.jasperreports.engine.JasperReport@12504e0}
DEBUG jr: net.sf.jasperreports.engine.data.JRMapCollectionDataSource@1630eb6
Apr 29, 2010 4:15:13 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet FootwearReportsServlet threw exception
java.lang.NullPointerException
at net.sf.jasperreports.engine.fill.JRFiller.fillReport(JRFiller.java:89)
at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:601)
at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:517)
at net.sf.jasperreports.engine.JasperRunManager.runReportToPdf(JasperRunManager.java:385)
at com.rsl.reports.FootwearReportsServlet.doGet(FootwearReportsServlet.java:287)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)
我不知道是空引用在哪里。从调试行中，我可以看到每个参数都有一个值。难道是指指向其中一张图片的错误路径？有任何想法吗？由于某种原因，我的服务器无法在Eclipse中以调试模式启动，因此我很难弄清楚这一点。
最佳答案
通过查看出现错误的行：
jasperreports.engine.fill.JRFiller.fillReport(JRFiller.java:89)
在JRFiller源代码中，它对应于
jasperPrint = filler.fill(parameters, dataSource);
在此行中唯一导致
NullPointerException的是filler为null的情况。此时，不会检查null的参数。查看
createFiller的代码（第134行），您可以轻松地看到该函数返回空指针的情况。因此，我想您以某种方式忘记了指定打印顺序（PRINT_ORDER_HORIZONTAL或PRINT_ORDER_VERTICAL）。