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Java example source code file (JMap.java)

This example Java source code file (JMap.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

all_objects_option, attachnotsupportedexception, class, default_option, exception, force_sa_option, hotspotvirtualmachine, inputstream, ioexception, jmap, live_objects_option, reflection, sa_tool_options, string, virtualmachine

The JMap.java Java example source code

/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.tools.jmap;

import java.lang.reflect.Method;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;

import com.sun.tools.attach.VirtualMachine;
import com.sun.tools.attach.AttachNotSupportedException;
import sun.tools.attach.HotSpotVirtualMachine;

/*
 * This class is the main class for the JMap utility. It parses its arguments
 * and decides if the command should be satisfied using the VM attach mechanism
 * or an SA tool. At this time the only option that uses the VM attach mechanism
 * is the -dump option to get a heap dump of a running application. All other
 * options are mapped to SA tools.
 */
public class JMap {

    // Options handled by the attach mechanism
    private static String HISTO_OPTION = "-histo";
    private static String LIVE_HISTO_OPTION = "-histo:live";
    private static String DUMP_OPTION_PREFIX = "-dump:";

    // These options imply the use of a SA tool
    private static String SA_TOOL_OPTIONS =
      "-heap|-heap:format=b|-clstats|-finalizerinfo";

    // The -F (force) option is currently not passed through to SA
    private static String FORCE_SA_OPTION = "-F";

    // Default option (if nothing provided)
    private static String DEFAULT_OPTION = "-pmap";

    public static void main(String[] args) throws Exception {
        if (args.length == 0) {
            usage(1); // no arguments
        }

        // used to indicate if we should use SA
        boolean useSA = false;

        // the chosen option (-heap, -dump:*, ... )
        String option = null;

        // First iterate over the options (arguments starting with -).  There should be
        // one (but maybe two if -F is also used).
        int optionCount = 0;
        while (optionCount < args.length) {
            String arg = args[optionCount];
            if (!arg.startsWith("-")) {
                break;
            }
            if (arg.equals("-help") || arg.equals("-h")) {
                usage(0);
            } else if (arg.equals(FORCE_SA_OPTION)) {
                useSA = true;
            } else {
                if (option != null) {
                    usage(1);  // option already specified
                }
                option = arg;
            }
            optionCount++;
        }

        // if no option provided then use default.
        if (option == null) {
            option = DEFAULT_OPTION;
        }
        if (option.matches(SA_TOOL_OPTIONS)) {
            useSA = true;
        }

        // Next we check the parameter count. For the SA tools there are
        // one or two parameters. For the built-in -dump option there is
        // only one parameter (the process-id)
        int paramCount = args.length - optionCount;
        if (paramCount == 0 || paramCount > 2) {
            usage(1);
        }

        if (optionCount == 0 || paramCount != 1) {
            useSA = true;
        } else {
            // the parameter for the -dump option is a process-id.
            // If it doesn't parse to a number then it must be SA
            // debug server
            if (!args[optionCount].matches("[0-9]+")) {
                useSA = true;
            }
        }


        // at this point we know if we are executing an SA tool or a built-in
        // option.

        if (useSA) {
            // parameters (<pid> or  )
            String params[] = new String[paramCount];
            for (int i=optionCount; i<args.length; i++ ){
                params[i-optionCount] = args[i];
            }
            runTool(option, params);

        } else {
            String pid = args[1];
            // Here we handle the built-in options
            // As more options are added we should create an abstract tool class and
            // have a table to map the options
            if (option.equals(HISTO_OPTION)) {
                histo(pid, false);
            } else if (option.equals(LIVE_HISTO_OPTION)) {
                histo(pid, true);
            } else if (option.startsWith(DUMP_OPTION_PREFIX)) {
                dump(pid, option);
            } else {
                usage(1);
            }
        }
    }

    // Invoke SA tool  with the given arguments
    private static void runTool(String option, String args[]) throws Exception {
        String[][] tools = {
            { "-pmap",          "sun.jvm.hotspot.tools.PMap"             },
            { "-heap",          "sun.jvm.hotspot.tools.HeapSummary"      },
            { "-heap:format=b", "sun.jvm.hotspot.tools.HeapDumper"       },
            { "-histo",         "sun.jvm.hotspot.tools.ObjectHistogram"  },
            { "-clstats",       "sun.jvm.hotspot.tools.ClassLoaderStats" },
            { "-finalizerinfo", "sun.jvm.hotspot.tools.FinalizerInfo"    },
        };

        String tool = null;

        // -dump option needs to be handled in a special way
        if (option.startsWith(DUMP_OPTION_PREFIX)) {
            // first check that the option can be parsed
            String fn = parseDumpOptions(option);
            if (fn == null) {
                usage(1);
            }

            // tool for heap dumping
            tool = "sun.jvm.hotspot.tools.HeapDumper";

            // HeapDumper -f <file>
            args = prepend(fn, args);
            args = prepend("-f", args);
        } else {
            int i=0;
            while (i < tools.length) {
                if (option.equals(tools[i][0])) {
                    tool = tools[i][1];
                    break;
                }
                i++;
            }
        }
        if (tool == null) {
            usage(1);   // no mapping to tool
        }

        // Tool not available on this  platform.
        Class<?> c = loadClass(tool);
        if (c == null) {
            usage(1);
        }

        // invoke the main method with the arguments
        Class[] argTypes = { String[].class } ;
        Method m = c.getDeclaredMethod("main", argTypes);

        Object[] invokeArgs = { args };
        m.invoke(null, invokeArgs);
    }

    // loads the given class using the system class loader
    private static Class<?> loadClass(String name) {
        //
        // We specify the system clas loader so as to cater for development
        // environments where this class is on the boot class path but sa-jdi.jar
        // is on the system class path. Once the JDK is deployed then both
        // tools.jar and sa-jdi.jar are on the system class path.
        //
        try {
            return Class.forName(name, true,
                                 ClassLoader.getSystemClassLoader());
        } catch (Exception x)  { }
        return null;
    }

    private static final String LIVE_OBJECTS_OPTION = "-live";
    private static final String ALL_OBJECTS_OPTION = "-all";
    private static void histo(String pid, boolean live) throws IOException {
        VirtualMachine vm = attach(pid);
        InputStream in = ((HotSpotVirtualMachine)vm).
            heapHisto(live ? LIVE_OBJECTS_OPTION : ALL_OBJECTS_OPTION);
        drain(vm, in);
    }

    private static void dump(String pid, String options) throws IOException {
        // parse the options to get the dump filename
        String filename = parseDumpOptions(options);
        if (filename == null) {
            usage(1);  // invalid options or no filename
        }

        // get the canonical path - important to avoid just passing
        // a "heap.bin" and having the dump created in the target VM
        // working directory rather than the directory where jmap
        // is executed.
        filename = new File(filename).getCanonicalPath();

        // dump live objects only or not
        boolean live = isDumpLiveObjects(options);

        VirtualMachine vm = attach(pid);
        System.out.println("Dumping heap to " + filename + " ...");
        InputStream in = ((HotSpotVirtualMachine)vm).
            dumpHeap((Object)filename,
                     (live ? LIVE_OBJECTS_OPTION : ALL_OBJECTS_OPTION));
        drain(vm, in);
    }

    // Parse the options to the -dump option. Valid options are format=b and
    // file=<file>. Returns  if provided. Returns null if  not
    // provided, or invalid option.
    private static String parseDumpOptions(String arg) {
        assert arg.startsWith(DUMP_OPTION_PREFIX);

        String filename = null;

        // options are separated by comma (,)
        String options[] = arg.substring(DUMP_OPTION_PREFIX.length()).split(",");

        for (int i=0; i<options.length; i++) {
            String option = options[i];

            if (option.equals("format=b")) {
                // ignore format (not needed at this time)
            } else if (option.equals("live")) {
                // a valid suboption
            } else {

                // file=<file> - check that  is specified
                if (option.startsWith("file=")) {
                    filename = option.substring(5);
                    if (filename.length() == 0) {
                        return null;
                    }
                } else {
                    return null;  // option not recognized
                }
            }
        }
        return filename;
    }

    private static boolean isDumpLiveObjects(String arg) {
        // options are separated by comma (,)
        String options[] = arg.substring(DUMP_OPTION_PREFIX.length()).split(",");
        for (String suboption : options) {
            if (suboption.equals("live")) {
                return true;
            }
        }
        return false;
    }

    // Attach to <pid>, existing if we fail to attach
    private static VirtualMachine attach(String pid) {
        try {
            return VirtualMachine.attach(pid);
        } catch (Exception x) {
            String msg = x.getMessage();
            if (msg != null) {
                System.err.println(pid + ": " + msg);
            } else {
                x.printStackTrace();
            }
            if ((x instanceof AttachNotSupportedException) && haveSA()) {
                System.err.println("The -F option can be used when the " +
                  "target process is not responding");
            }
            System.exit(1);
            return null; // keep compiler happy
        }
    }

    // Read the stream from the target VM until EOF, then detach
    private static void drain(VirtualMachine vm, InputStream in) throws IOException {
        // 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();
    }

    // return a new string array with arg as the first element
    private static String[] prepend(String arg, String args[]) {
        String[] newargs = new String[args.length+1];
        newargs[0] = arg;
        System.arraycopy(args, 0, newargs, 1, args.length);
        return newargs;
    }

    // returns true if SA is available
    private static boolean haveSA() {
        Class<?> c = loadClass("sun.jvm.hotspot.tools.HeapSummary");
        return (c != null);
    }

    // print usage message
    private static void usage(int exit) {
        System.err.println("Usage:");
        if (haveSA()) {
            System.err.println("    jmap [option] <pid>");
            System.err.println("        (to connect to running process)");
            System.err.println("    jmap [option] <executable ");
            System.err.println("                         Example: jmap -dump:live,format=b,file=heap.bin <pid>");
            System.err.println("    -F                   force. Use with -dump:<dump-options>  or -histo");
            System.err.println("                         to force a heap dump or histogram when <pid> does not");
            System.err.println("                         respond. The \"live\" suboption is not supported");
            System.err.println("                         in this mode.");
            System.err.println("    -h | -help           to print this help message");
            System.err.println("    -J<flag>             to pass  directly to the runtime system");
        } else {
            System.err.println("    jmap -histo <pid>");
            System.err.println("      (to connect to running process and print histogram of java object heap");
            System.err.println("    jmap -dump:<dump-options> ");
            System.err.println("      (to connect to running process and dump java heap)");
            System.err.println("");
            System.err.println("    dump-options:");
            System.err.println("      format=b     binary default");
            System.err.println("      file=<file>  dump heap to ");
            System.err.println("");
            System.err.println("    Example:       jmap -dump:format=b,file=heap.bin <pid>");
        }

        System.exit(exit);
    }
}

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