Java – Tomcat multithreading deployment using managerservlet

I have 30 wars in tomcat, and there are dependencies between them So we have a servlet to deploy them sequentially Now I want to deploy the required applications in order, and then deploy them in parallel

My code is as follows

public class MyDeployerServlet extends ManagerServlet {
...
    public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException,ServletException {
...
if(count < serialContexts){
            super.deploy(writer,context,contextName,null,false,sm);
            count++;
        } else {
            MyAsyncDeployer deployer = new MyAsyncDeployer(writer,sm);
            Thread deployerThread = new Thread(deployer);
            deployerThread.start();
        }
}

The runnable code of myasyncdeployer is:

public class MyAsyncDeployer extends MyDeployerServlet implements Runnable{
    private PrintWriter writer;
    private String config;
    private ContextName context;
    private String war;
    private boolean update;
    private StringManager sm;

    public MyAsyncDeployer(PrintWriter writer,String config,ContextName context,String war,boolean update,StringManager sm) {
        this.writer = writer;
        this.config = config;
        this.context = context;
        this.war = war;
        this.update = update;
        this.sm = sm;
    }

    public void run() {
        super.deploy(writer,config,sm);
    }

When I call it this, serial deployment is fine, but multithreaded deployment throws exceptions

Exception in thread "Thread-9" java.lang.NullPointerException
        at javax.servlet.GenericServlet.getServletContext(GenericServlet.java:123)
        at javax.servlet.GenericServlet.log(GenericServlet.java:188)
        at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:834)
        at com.example.servlet.MyAsyncDeployer.run(MyAsyncDeployer.java:30)
        at java.lang.Thread.run(Thread.java:745)
Exception in thread "Thread-10" java.lang.NullPointerException
        at javax.servlet.GenericServlet.getServletContext(GenericServlet.java:123)
        at javax.servlet.GenericServlet.log(GenericServlet.java:188)
        at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:834)
        at com.example.servlet.MyAsyncDeployer.run(MyAsyncDeployer.java:30)
        at java.lang.Thread.run(Thread.java:745)

There's nothing I can do. What's missing here? I use the same object reference in my thread If possible, multi-threaded deployment?

Solution

The problem here is that you forgot to initialize your myasyncdeployer servlet

But as long as you don't need to deploy an asynchronous servlet into a container and only need to use its deployment capabilities, no one instantiates it for you

Fixed version code:

if(count < serialContexts){
            super.deploy(writer,sm);
            delpoyer.setWrapper(getWrapper());
            deployer.init(getServletConfig());
            Thread deployerThread = new Thread(deployer);
            deployerThread.start();
        }
}

UPD: notice that you can not avoid creating servlet (that is, calling this.deploy in Runnable#run), because the thread safety of ManagerServlet#deploy method is guaranteed by full synchronization (the whole method is synchronous), so in practice, such a method will be continuous.