Error in tomcat "too many open files"

Question

I have an application running on tomcat and sometimes I have the error below:

SEVERE: Socket accept failed
java.net.SocketException: Too many open files
at java.net.PlainSocketImpl.socketAccept(Native Method)
at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:398)
at java.net.ServerSocket.implAccept(ServerSocket.java:522)
at java.net.ServerSocket.accept(ServerSocket.java:490)
at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:60)
at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:216)
at java.lang.Thread.run(Thread.java:722)

....

SEVERE: Error processed default web.xml named conf/web.xml at /local/myApp/apache-tomcat/conf/web.xml
java.io.FileNotFoundException: /local/myApp/apache-tomcat/conf/web.xml (Too many open files)
        at java.io.FileInputStream.open(Native Method)
        at java.io.FileInputStream.<init>(FileInputStream.java:138)
        at org.apache.catalina.startup.ContextConfig.getWebXmlSource(ContextConfig.java:1838)
        at org.apache.catalina.startup.ContextConfig.getGlobalWebXmlSource(ContextConfig.java:1745)
        at org.apache.catalina.startup.ContextConfig.getDefaultWebXmlFragment(ContextConfig.java:1418)
        at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1253)
        at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:878)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:369)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5269)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
        at org.apache.catalina.core.StandardContext.reload(StandardContext.java:3926)
        at org.apache.catalina.loader.WebappLoader.backgroundProcess(WebappLoader.java:426)
        at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1345)
        at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1530)
        at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1540)
        at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1540)
        at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1519)
        at java.lang.Thread.run(Thread.java:722)

I check the limits of the open files and it's 1024 but when I check the number of open files of the application with lsof it's nearly 200, why this happen if it does not reach the limit? Should I increase the limit? Is there any other reason to get this error? The only way to get the service running correctly again, it's restarting the tomcat, is there another way of getting back to normal?

Thanks in advance.

EDIT: Here is the servlet which process the doPost method, at the beginning I didn't close every stream, could it be that? I added the finally statement for doing that:

    InputStream is = null;
    DataInputStream dis = null;
    OutputStream os = null;
    DataOutputStream dos = null;
    String paramName = "";
    try {
        os = response.getOutputStream();
        is = request.getInputStream();
        dis = new DataInputStream(is);
        dos = new DataOutputStream(os);
        .....
        }catch (Throwable e) {
        LOGGER.error(e.getMessage());
        } finally {
          if (dis != null) {
             dis.close();
           }
           else if(is != null) {
             is.close();
           }                
           if (dos != null) {
             dos.close();
           }
           else if( os != null) {
             os.close();
           }
        }

EDIT2: After making some testing I realize that if I close first the DataInputStream and then the InputStream, I get in the other part of the communication a number before the message(I don't know why). I changed the order of closing the stream and it seems that everything it's ok. But I still have the problem. Any idea?

  finally {

    if(is != null) {
        try {
            is.close();
        } catch (IOException e) {
            LOGGER.error(e.getMessage());
        }
    }
    if (dis != null) {
        try {
            dis.close();
        } catch (IOException e) {
            LOGGER.error(e.getMessage());
        }
    }
    if(os != null) {
        try {
            os.close();
        } catch (IOException e) {
            LOGGER.error(e.getMessage());
        }
    }
    if (dos != null) {
        try {
            dos.close();
        } catch (IOException e) {
            LOGGER.error(e.getMessage());
        }
    }
}

Answer 1

Do the following to get the pid, say 1234, of tomcat7

ps aux |grep tomcat7

and then do

cat /proc/1234/limits to read a line like the following

Max open files 16384 16384 files

These are the maximum number of open files that are allowed by Tomcat. To increase it, follow the instructions below

Too many open files Tomcat.