Easyexcel异常处理：getOutputStream() has already been called for this response

• 异常日志
• 源码位置
• 异常原因
• 异常前代码
• 调整后代码

java.lang.IllegalStateException: getOutputStream() has already been called for this response
	at org.apache.catalina.connector.Response.getWriter(Response.java:582) ~[tomcat-embed-core-9.0.17.jar!/:9.0.17]
	at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:227) ~[tomcat-embed-core-9.0.17.jar!/:9.0.17]
	at javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:152) ~[javax.servlet-api-3.1.0.jar!/:3.1.0]

看起来是，output流使用标志生效导致异常。

一句话总结：同一个请求中：调用了两次response.getOutputStream()方法。或者先进行了respose的头等信息设置后调用response.getOutputStream()

控制层：

    @RequestMapping(value ="/detailExport" ,method = RequestMethod.POST)
    @BusiResponseBody
    public void detailExport(@RequestBody IdReqBO queryBO, HttpServletRequest request,HttpServletResponse response ) {
    //获取导出的元数据（转换器、格式控制器、导出内容等）
        ExcelExportContent excelExportContent = excelExportStrategy.exportDetailExcelContent(request.getRequestURI(), queryBO);
        EasyExcelUtils.ExportResponse(excelExportContent,response);
    }

工具类：

public class EasyExcelUtils {

    public static void ExportResponse(ExcelExportContent excelExportContent,HttpServletResponse response){
        try {
            response.setContentType("application/vnd.ms-excel");
            response.setCharacterEncoding("utf-8");
            String fileName = URLEncoder.encode(excelExportContent.getFileName(), "UTF-8").replaceAll("\+", "%20");
            response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + fileName + ".xlsx");
			//这里先设置的response的头、编码等信息，导致response.getOutputStream()时异常
            ExcelWriterBuilder excelWriterBuilder = EasyExcel.write(response.getOutputStream(), excelExportContent.getAccountDataClass())
                    .registerConverter(new BigDecimalStringConverter())
                    .registerConverter(new DateStringConverter());
            List writeHandler = excelExportContent.getWriteHandler();
            for (WriteHandler handler : writeHandler) {
                excelWriterBuilder.registerWriteHandler(handler);
            }
            excelWriterBuilder
                    .sheet(excelExportContent.getSheetName())
                    .doWrite(excelExportContent.getAccountData());
        } catch (Exception e){
            e.printStackTrace();
            throw new ZTBusinessException(e.getMessage());
        }
    }
}

控制层不变：

    @RequestMapping(value ="/detailExport" ,method = RequestMethod.POST)
    @BusiResponseBody
    public void detailExport(@RequestBody IdReqBO queryBO, HttpServletRequest request,HttpServletResponse response ) {
    //获取导出的元数据（转换器、格式控制器、导出内容等），可忽略
        ExcelExportContent excelExportContent = excelExportStrategy.exportDetailExcelContent(request.getRequestURI(), queryBO);
        EasyExcelUtils.ExportResponse(excelExportContent,response);
    }

工具类：
这里格式化response的动作只能在response.getOutputStream()之后，在EasyExcel的doWrite之前。
在response.getOutputStream()之前会出现getOutputStream() has already been called for this response异常。在EasyExcel的doWrite之后，流已经被写回了，格式化response不会生效，写回的内容是txt格式。

public class EasyExcelUtils {

    protected static Logger logger = LoggerFactory.getLogger(EasyExcelUtils.class);

    public static void ExportResponse(ExcelExportContent excelExportContent, HttpServletResponse response) {
        try {
                ExcelWriterBuilder excelWriterBuilder = EasyExcel.write(response.getOutputStream());
                //这里格式化response内容只能在这个位置
                FormatResponse(response, excelExportContent.getFileName());
                ExcelWriterSheetBuilder(excelWriterBuilder, excelExportContent).doWrite(excelExportContent.getDetailData());
        } catch (Exception e) {
            e.printStackTrace();
            throw new ZTBusinessException("ExportResponse exception:" + e.getMessage());
        }
    }

    public static void FormatResponse(HttpServletResponse response, String fileName) {
        try {
            response.setContentType("application/vnd.ms-excel");
            response.setCharacterEncoding("utf-8");
            String exportFileName = URLEncoder.encode(fileName, "UTF-8").replaceAll("\+", "%20");
            response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + exportFileName + ".xlsx");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            throw new ZTBusinessException("FormatResponse exception:" + e.getMessage());
        }
    }

    private static ExcelWriterSheetBuilder ExcelWriterSheetBuilder(ExcelWriterBuilder excelWriterBuilder, ExcelExportContent excelExportContent) {
        List converterList = Optional.ofNullable(excelExportContent.getConverter()).orElseGet(ArrayList::new);
        for (Converter converter : converterList) {
            excelWriterBuilder.registerConverter(converter);
        }
        List writeHandlerList = Optional.ofNullable(excelExportContent.getWriteHandler()).orElseGet(ArrayList::new);
        for (WriteHandler writeHandler : writeHandlerList) {
            excelWriterBuilder.registerWriteHandler(writeHandler);
        }
        ExcelWriterSheetBuilder excelWriterSheetBuilder = excelWriterBuilder.sheet(excelExportContent.getSheetName());
        return excelWriterSheetBuilder;
    }

}