将一个巨大的字符串作为post参数传递给servlet

Question

我有一个servlet，它接收一个巨大的字符串(大约301695个长度)作为post参数。

每分钟，.net应用程序都会向servlet发送如此巨大的字符串。

最初我用来获取字符串，如下所示：

 Line 1: String str = request.getParameter("data");

但是，在3-4个小时后。我得到了以下异常：

 java.lang.OutOfMemoryError: Java heap space

然后我注释了Line: 1。尽管我的servlet代码没有接收到字符串，但我得到了与上面提到的相同的异常。

请给我引路。我应该如何处理这个问题？我读了很多关于它的博客和文章，增加了堆的大小和其他东西。但是，还没有找到任何解决方案。

原始代码如下：

private String scanType = "";
private static final String path = "D:\\Mobile_scan_alerts";
private static final String stockFileName = "stock.txt";
private static final String foFileName = "fo.txt";
private static Logger logger = null;
private String currDate = "";
private DateFormat dateFormat;
private StringBuffer stockData;
private StringBuffer foData;
 StringBuffer data = new StringBuffer("");
// For average time of received data
private static float sum = 0;
private static float count = 0;
private static float s_sum = 0;
private static float s_count = 0;
private static float fo_sum = 0;
private static float fo_count = 0;

private static final File dir = new File(path);
private static final File stockFile = new File(path + "\\" + stockFileName);
private static final File foFile = new File(path + "\\" + foFileName);

public void init() {

    logger = MyLogger.getScanAlertLogger();

    if(logger == null) {
        MyLogger.createLog();
        logger = MyLogger.getScanAlertLogger();
    }

}

/**
 * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
 * methods.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    PrintWriter out = response.getWriter();
    response.setContentType("text/plain");
    String strScan = "";

    try {

        String asof = null;

        scanType = request.getParameter("type");
        scanType = scanType == null ? "" : scanType;


        if(scanType.length() > 0){

            if(scanType.equalsIgnoreCase("s")) {
                stockData = null;
                stockData = new StringBuffer(request.getParameter("scanData"));
                stockData = stockData == null ? new StringBuffer("") : stockData;
            } else {
                foData = null;
                foData = new StringBuffer(request.getParameter("scanData"));
                foData = foData == null ? new StringBuffer("") : foData;
            }

        }

        asof = request.getParameter("asof");
        asof = asof == null ? "" : asof.trim();

        // Date format without seconds
        DateFormat formatWithoutSec = new SimpleDateFormat("yyyy/MM/dd HH:mm");

        dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date tmp = new Date();

        // format: yyyy/MM/dd HH:mm:ss
        currDate = dateFormat.format(tmp);

        //format: yyyy/MM/dd HH:mm
        Date asofDate = formatWithoutSec.parse(asof);
        Date cDate = formatWithoutSec.parse(currDate);
        cDate.setSeconds(0);


        System.out.println(asofDate.toString()+" || "+cDate.toString());

        int isDataExpired = asofDate.toString().compareTo(cDate.toString());

        if(isDataExpired > 0 || isDataExpired == 0) {

            if(scanType != null && scanType.length() > 0) {
                checkAndCreateDir();
                strScan = scanType.equalsIgnoreCase("s") ? "Stock Data Recieved at "+currDate
                        : "FO Data Recieved at "+currDate;
                //System.out.println(strScan);
            } else {
                strScan = "JSON of scan data not received properly at "+currDate;
                //System.out.println("GSAS: received null or empty");
            }

        } else {
            strScan = "GSAS: " + scanType + ": Received Expired Data of "+asofDate.toString()+" at "+cDate.toString();
            System.out.println(strScan);
        }
        scanType = null;


    } catch (Exception ex) {
        strScan = "Mobile server issue for receiving scan data";
        System.out.println("GSAS: Exception-1: "+ex);
        logger.error("GetScanAlertServlet: processRequest(): Exception: "+ex.toString());
    } finally {
        logger.info("GetScanAlertServlet: "+strScan);
        out.println(strScan);
    }

}

private void checkAndCreateDir() {

    try {
            boolean isStock = false;
            Date ddate = new Date();
            currDate = dateFormat.format(ddate);
            sum += ddate.getSeconds();
            count++;
            logger.info("Total Average Time: "+(sum/count));

            if(scanType.equalsIgnoreCase("s")){ //For Stock
                setStockData(stockData);

                Date date1 = new Date();
                currDate = dateFormat.format(date1);
                s_sum += date1.getSeconds();
                s_count++;
                logger.info("Stock Average Time: "+(s_sum/s_count));

                //file = new File(path + "\\" + stockFileName);
                isStock = true;

            } else if (scanType.equalsIgnoreCase("fo")) { //For FO
                setFOData(foData);

                Date date2 = new Date();
                currDate = dateFormat.format(date2);
                fo_sum += date2.getSeconds();
                fo_count++;
                logger.info("FO Average Time: "+(fo_sum/fo_count));

                //file = new File(path + "\\" +foFileName);
                isStock = false;
            }


            if(!dir.exists()) { // Directory not exists
                if(dir.mkdir()) {

                    if(isStock)
                        checkAndCreateFile(stockFile);
                    else
                        checkAndCreateFile(foFile);

                }
            } else { // Directory already exists

                    if(isStock)
                        checkAndCreateFile(stockFile);
                    else
                        checkAndCreateFile(foFile);
            }

    } catch (Exception e) {
        System.out.println("GSAS: Exception-2: "+e);
        logger.error("GetScanAlertServlet: checkAndCreateDir(): Exception: "+e);
    }

}

private void checkAndCreateFile(File file) {

    try{
        if(!file.exists()){ // File not exists

            if(file.createNewFile()){
                writeToFile(file);
            }

        } else { // File already exists
            writeToFile(file);
        }
    } catch (Exception e) {
        System.out.println("GSAS: Exception-3: "+e);
        logger.error("GetScanAlertServlet: checkAndCreateFile(): Exception: "+e.toString());
    }
}


private void writeToFile(File file) {

    FileOutputStream fop = null;

    try{

        if(scanType.equalsIgnoreCase("s")){ //For Stock
            data = getStockData();
        } else if (scanType.equalsIgnoreCase("fo")) { //For FO
            data = getFOData();
        }

        if(data != null && data.length() > 0 && file != null){

            fop = new FileOutputStream(file);

            byte[] contentBytes = data.toString().getBytes();
            for(byte b : contentBytes){
                fop.write(b);
            }
            //fop.write(contentBytes);

            fop.flush();


        } else {

            System.out.println("GSAS: Data is null/empty string");
            logger.info("GSAS: Data is null or empty string");

        }
        data = null;
    } catch (Exception  e) {
        System.out.println("GSAS: Exception-4: "+e);
        logger.info("GetScanAlertServlet: writeToFile(): Exception: "+e.toString());

    } finally {

        try {

            if(fop != null)
                fop.close();

        } catch (IOException ex) {
                java.util.logging.Logger.getLogger(GetScanAlertServlet.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

private String readFromFile(String fileName){

    String fileContent = "";
    try{

        String temp = "";
        File file = new File(fileName);
        if(file.exists()){

            FileReader fr = new FileReader(file);
            BufferedReader br = new BufferedReader(fr);

            while((temp = br.readLine()) != null)
            {
                fileContent += temp;
            }
            br.close();
        } else {
            System.out.println("GSAS: File not exists to read");
            logger.info("GetScanAlertServlet: File not exists to read");
        }

        temp = null;
        file = null;

    } catch (Exception e) {
        System.out.println("GSAS: Exception-5: "+e);
        logger.error("GetScanAlertServlet: readFromFile(): Exception: "+e.toString());
    }
    return fileContent;
}

public StringBuffer getStockData() {

    //String temp="";
    //StringBuffer temp = (StringBuffer)scanDataSession.getAttribute("stock");
    //if(temp != null && temp.length() > 0) {
    //    return temp;
    //}
    if(stockData != null && stockData.length() > 0){
        return stockData;
    } else {
        stockData = null;
        stockData = new StringBuffer(readFromFile(path + "\\"+ stockFileName));
        return stockData;
    }
}


public StringBuffer getFOData(){

    //String temp="";
    //StringBuffer temp = (StringBuffer)scanDataSession.getAttribute("fo");
    //if(temp != null && temp.length() > 0) {
    //    return temp;
    //}
    if(foData != null && foData.length() > 0) {
        return foData; 
    } else {
        foData = null;
        foData = new StringBuffer(readFromFile(path + "\\" + foFileName));
        return foData;
    }   
}

}

Answer 1

增加堆大小不是解决此问题的好方法。上游应用程序应该停止向Servlet发送巨大的字符串。

上游(.net)应用程序应该考虑将所有数据写入文件，只需要将文件的位置作为参数发送到Servlet即可。一旦servlet收到来自上游的通知，您就可以考虑从该位置下载/读取文件。

然后我注释了行: 1.尽管我的servlet代码没有接收到字符串(如注释)，但我得到了与上面提到的相同的异常。

行:1是读取数据。如果你注释它，你将不会收到字符串。

Answer 2

您可以使用apache commons-fileupload库流API，这样，您就可以将上传的文件作为流，并将其写入该文件：

ServletFileUpload upload = new ServletFileUpload();

// Parse the request
FileItemIterator iter = upload.getItemIterator(request);
while (iter.hasNext()) {
    FileItemStream item = iter.next();
    String name = item.getFieldName();
    InputStream stream = item.openStream();
    if (item.isFormField()) {
        System.out.println("Form field " + name + " with value "
            + Streams.asString(stream) + " detected.");
    } else {
        System.out.println("File field " + name + " with file name "
            + item.getName() + " detected.");
        // Process the input stream
        ...
    }
}

现在您有了InputStream，所以可以将其写入输出流中。

但是要使用它，您需要您的.NET应用程序将字节上传到服务器，而不是将整个字符串作为请求参数发送。

http://commons.apache.org/proper/commons-fileupload/streaming.html

Answer 3

如果您无法控制传递给servlet的字符串，请检查您的VM参数并相应地修改它们。例如：

set JAVA_OPTS=-Dfile.encoding=UTF-8 -Xms128m -Xmx1024m -XX:PermSize=64m -XX:MaxPermSize=256m

查看完整的解释here。