【说站】java中Thread Dump是什么

public class JStack {
            public static void main(String[] args) throws Exception {
               ...
                    String pid = args[optionCount];
                    String params[];
                    if (locks) {
                        params = new String[] { "-l" };
                    } else {
                        params = new String[0];
                    }
                    runThreadDump(pid, params);
                ...
            }
            // Attach to pid and perform a thread dump
            private static void runThreadDump(String pid, String args[])
                    throws Exception {
                VirtualMachine vm = null;
                try {
                    vm = VirtualMachine.attach(pid);
                } catch (Exception x) {
                   ...
                }
                // Cast to HotSpotVirtualMachine as this is implementation specific
                // method.
                InputStream in = ((HotSpotVirtualMachine) vm)
                        .remoteDataDump((Object[]) args);
                // read to EOF and just print output
                byte b[] = new byte[256];
                int n;
                do {
                    n = in.read(b);
                    if (n > 0) {
                        String s = new String(b, 0, n, "UTF-8");
                        System.out.print(s);
                    }
                } while (n > 0);
                in.close();
                vm.detach();
            }