java.lang.IllegalStateException 从网络服务器下载文件时出现 servlet 异常

Question

我有一些从网络服务器下载文件的代码。一切正常，但在控制台中我有这个异常：

        июн 26, 2015 2:08:42 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [default] in context with path [/TestTask] threw exception
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
    at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:462)
    at org.apache.struts2.dispatcher.DefaultDispatcherErrorHandler.handleErrorInDevMode(DefaultDispatcherErrorHandler.java:109)
    at org.apache.struts2.dispatcher.DefaultDispatcherErrorHandler.handleError(DefaultDispatcherErrorHandler.java:57)
    at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:909)
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:576)
    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:526)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:655)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

为什么以及可能是什么？我该如何解决这个问题？我尝试在 google 中找到答案，但我失败了。

代码：

package actions;

import java.io.IOException;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.xml.ws.Action;

import org.apache.log4j.Logger;
import org.apache.struts.chain.contexts.ServletActionContext;

import service.CsvCreator;

import com.opensymphony.xwork2.ActionSupport;

public class DownloadCsvAction extends ActionSupport {

    private static final long serialVersionUID = -4714537109287679996L;
    private CsvCreator CSVcreator;
    private static final Logger logger = Logger.getLogger(DownloadCsvAction.class);

    public CsvCreator getCSVcreator() {
        return CSVcreator;
    }

    public void setCSVcreator(CsvCreator cSVcreator) {
        CSVcreator = cSVcreator;
    }

    @Override
    public String execute() {

        HttpServletResponse response = org.apache.struts2.ServletActionContext.getResponse();
        response.setHeader("Content-Disposition", "attachment; filename=\"phone_records.csv\"");
        response.setContentType("text/csv");

        ServletOutputStream out;
        try {
            out = response.getOutputStream();

            String tableHeader = "Caller, Event, Reciever, Timestamp\n";

            out.write(tableHeader.getBytes("UTF-8"));
            out.write(CSVcreator.getAllRecordsInString().getBytes("UTF-8"));
            
            out.flush();
            out.close();
        } catch (IOException e) {
            logger.error(e.getMessage());
        }

        return SUCCESS;
    }

}

还有我的struts.xml:

<action name="DownloadCsvAction" class="DownloadCsvAction">
        <result name="success" type="dispatcher"/>
</action>

Answer 1

Why and what it can be?

因为响应已经提交。 Struts2 使用之前您已关闭响应。

And how I can fix this problem?

当您的操作执行结束时，return Action.NONE 结果代码。此代码告诉调用者不要执行任何结果，因为响应可能已经提交。

您还可以重写操作实现以使用 stream 结果类型。通过这种方式，您不必处理响应，让 Struts2 完成其余的工作。使用 stream 结果的示例是 here。

java.lang.IllegalStateException 从网络服务器下载文件时出现 servlet 异常

java.lang.IllegalStateException servlet exception when download file from web server

java

servlets

struts2

download

stream