我创建了一段代码，用于在servlet中生成和下载excel文件。下面提供了代码：
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String act = request.getParameter("act").toLowerCase();
RequestDispatcher rd = request.getRequestDispatcher("sqleditor.jsp");
try {
if(act.equalsIgnoreCase("exec")) {
String uqry = request.getParameter("isql");
if ( !uqry.isEmpty() ) {
qp = new queryProcessor(uqry);
mp = qp.getResultSet();
request.setAttribute("result",mp);
rd.forward(request, response);
} else {
ERROR_MSG = "Please enter a query";
request.setAttribute("errormsg", ERROR_MSG);
rd.forward(request, response);
}
} else if (act.equalsIgnoreCase("excel")) {
String uqry = request.getParameter("isql");
if ( !uqry.isEmpty() ) {
try {
response.setContentType("application/vnd.ms-excel");
response.setHeader("Content-Disposition", "attachment; filename=\"" + FILENAME + "\"");
initExcelfile(response.getOutputStream());
} catch (Exception evar1) {
request.setAttribute("errormsg", evar1.getMessage());
rd.forward(request, response);
}
System.out.println("File downloaded at client successfully");
}
}
} catch (AppException evar2) {
request.setAttribute("errormsg", evar2.getmessage());
rd.forward(request, response);
} catch (SQLException evar3) {
request.setAttribute("errormsg", evar3.getMessage());
rd.forward(request, response);
} catch (NullPointerException evar4) {
request.setAttribute("errormsg", evar4.getMessage());
rd.forward(request, response);
} catch (FileNotFoundException evar5) {
request.setAttribute("errormsg", evar5.getMessage());
rd.forward(request, response);
} catch (Exception evar6) {
request.setAttribute("errormsg", evar6.getMessage());
rd.forward(request, response);
}
}
private void initExcelfile(ServletOutputStream outputStream) {
HSSFWorkbook workbook = new HSSFWorkbook();
HSSFSheet sheet = workbook.createSheet("Datatypes");
Object[][] datatypes = {
{"Datatype", "Type", "Size(in bytes)"},
{"int", "Primitive", 2},
{"float", "Primitive", 4},
{"double", "Primitive", 8},
{"char", "Primitive", 1},
{"String", "Non-Primitive", "No fixed size"}
};
int rowNum = 0;
System.out.println("Creating excel");
for (Object[] datatype : datatypes) {
Row row = sheet.createRow(rowNum++);
int colNum = 0;
for (Object field : datatype) {
Cell cell = row.createCell(colNum++);
if (field instanceof String) {
cell.setCellValue((String) field);
} else if (field instanceof Integer) {
cell.setCellValue((Integer) field);
}
}
}
System.out.println("Workbook Created");
try {
workbook.write(outputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
但是当我将initExcelfile（）方法移至单独的类文件并从那里调用该方法时，会收到以下错误：
ERROR [io.undertow.request] (default task-4) UT005023: Exception handling request to /sqle/sqleditor.jsp: java.lang.RuntimeException: java.lang.IllegalStateException: UT010006: Cannot call getWriter(), getOutputStream() already called
at io.undertow.servlet.spec.RequestDispatcherImpl.forwardImpl(RequestDispatcherImpl.java:245)
at io.undertow.servlet.spec.RequestDispatcherImpl.forwardImplSetup(RequestDispatcherImpl.java:147)
at io.undertow.servlet.spec.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:111)
at com.sqle.RequestController.doPost(RequestController.java:84)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)
at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)
at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202)
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:805)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalStateException: UT010006: Cannot call getWriter(), getOutputStream() already called
at io.undertow.servlet.spec.HttpServletResponseImpl.getWriter(HttpServletResponseImpl.java:355)
at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:112)
at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:105)
at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:183)
at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:121)
at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:75)
at org.apache.jsp.sqleditor_jsp._jspService(sqleditor_jsp.java:196)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:402)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:346)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.jsp.JspFileHandler.handleRequest(JspFileHandler.java:32)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:274)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchToPath(ServletInitialHandler.java:209)
at io.undertow.servlet.spec.RequestDispatcherImpl.forwardImpl(RequestDispatcherImpl.java:221)
... 42 more
请让我知道我在这里遇到的错误，因为我遇到了这个错误。
答案 0 :(得分：0)
基于stacktrace，看来您是第一次这样做：
initExcelfile(response.getOutputStream())
这将引发异常。然后，在异常处理程序中，您似乎正在尝试重定向到JSP以产生错误消息。不幸的是，这失败了，因为：
getWriter()来找到发送其输出的位置，getOutputStream()，并且getWriter()对象上同时调用getOutputStream()和Response……否则您将获得IllegalStateException！如果要直接将电子表格写入输出，则在发生故障时无法重定向到JSP。即使servlet框架允许（不允许！），您也可能会得到部分电子表格，并在最后加上错误页面。用户的网络浏览器将无法理解这一点。
有两种选择：
首先还有一个引起异常的问题。我看不到明显的线索，因此您需要自己调试。 （例如，您可以连接调试器并在异常处理程序中设置断点，然后查看捕获的异常的类，消息和调用堆栈。）