--- a/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/CommandProcessor.java	Thu Apr 09 03:51:32 2020 +0000
+++ b/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/CommandProcessor.java	Wed Apr 08 21:01:01 2020 -0700
@@ -27,6 +27,7 @@
 import java.io.BufferedOutputStream;
 import java.io.BufferedReader;
 import java.io.ByteArrayOutputStream;
+import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
@@ -80,6 +81,7 @@
 import sun.jvm.hotspot.tools.StackTrace;
 import sun.jvm.hotspot.tools.jcore.ClassDump;
 import sun.jvm.hotspot.tools.jcore.ClassFilter;
+import sun.jvm.hotspot.tools.jcore.ClassWriter;
 import sun.jvm.hotspot.types.CIntegerType;
 import sun.jvm.hotspot.types.Field;
 import sun.jvm.hotspot.types.Type;
@@ -1703,6 +1705,66 @@
                 }
             }
         },
+        new Command("dumpclass", "dumpclass {address | name} [directory]", false) {
+            public void doit(Tokens t) {
+                int tokenCount = t.countTokens();
+                if (tokenCount != 1 && tokenCount != 2) {
+                    usage();
+                    return;
+                }
+
+                /* Find the InstanceKlass for specified class name or class address. */
+                InstanceKlass ik = null;
+                String classname = t.nextToken();
+                if (classname.startsWith("0x")) {
+                    // treat it as address
+                    VM vm = VM.getVM();
+                    Address addr = vm.getDebugger().parseAddress(classname);
+                    Metadata metadata = Metadata.instantiateWrapperFor(addr.addOffsetTo(0));
+                    if (metadata instanceof InstanceKlass) {
+                        ik = (InstanceKlass) metadata;
+                    } else {
+                        System.out.println("Specified address is not an InstanceKlass");
+                        return;
+                    }
+                } else {
+                    ik = SystemDictionaryHelper.findInstanceKlass(classname);
+                    if (ik == null) {
+                        System.out.println("class not found: " + classname);
+                        return;
+                    }
+                }
+
+                /* Compute filename for class. */
+                StringBuffer buf = new StringBuffer();
+                if (tokenCount > 1) {
+                    buf.append(t.nextToken());
+                } else {
+                    buf.append('.');
+                }
+                buf.append(File.separatorChar);
+                buf.append(ik.getName().asString().replace('/', File.separatorChar));
+                buf.append(".class");
+                String fileName = buf.toString();
+                File file = new File(fileName);
+
+                /* Dump the class file. */
+                try {
+                    int index = fileName.lastIndexOf(File.separatorChar);
+                    File dir = new File(fileName.substring(0, index));
+                    dir.mkdirs();
+                    try (FileOutputStream fos = new FileOutputStream(file)) {
+                        ClassWriter cw = new ClassWriter(ik, fos);
+                        cw.write();
+                    }
+                } catch (Exception e) {
+                    err.println("Error: " + e);
+                    if (verboseExceptions) {
+                        e.printStackTrace(err);
+                    }
+                }
+            }
+        },
         new Command("dumpheap", "dumpheap [filename]", false) {
             public void doit(Tokens t) {
                 if (t.countTokens() > 1) {

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/serviceability/sa/ClhsdbDumpclass.java	Wed Apr 08 21:01:01 2020 -0700
@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2020, 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.
+ *
+ * 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.
+ */
+
+import java.io.File;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import jdk.test.lib.apps.LingeredApp;
+import jdk.test.lib.JDKToolLauncher;
+import jdk.test.lib.JDKToolFinder;
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.SA.SATestUtils;
+import jtreg.SkippedException;
+
+/**
+ * @test
+ * @bug 8240990
+ * @summary Test clhsdb dumpclass command
+ * @requires vm.hasSA
+ * @library /test/lib
+ * @run main/othervm ClhsdbDumpclass
+ */
+
+public class ClhsdbDumpclass {
+    static final String APP_DOT_CLASSNAME = LingeredApp.class.getName();
+    static final String APP_SLASH_CLASSNAME = APP_DOT_CLASSNAME.replace('.', '/');
+
+    public static void main(String[] args) throws Exception {
+        System.out.println("Starting ClhsdbDumpclass test");
+
+        LingeredApp theApp = null;
+        try {
+            ClhsdbLauncher test = new ClhsdbLauncher();
+
+            theApp = LingeredApp.startApp();
+            System.out.println("Started LingeredApp with pid " + theApp.getPid());
+
+            // Run "dumpclass jdk/test/lib/apps/LingeredApp"
+            String cmd = "dumpclass " + APP_DOT_CLASSNAME;
+            List<String> cmds = List.of(cmd);
+            Map<String, List<String>> unExpStrMap = new HashMap<>();
+            unExpStrMap.put(cmd, List.of("class not found"));
+            test.run(theApp.getPid(), cmds, null, unExpStrMap);
+            File classFile = new File(APP_SLASH_CLASSNAME + ".class");
+            if (!classFile.exists()) {
+                throw new RuntimeException("FAILED: Cannot find dumped .class file");
+            }
+
+            // Run javap on the generated class file to make sure it's valid.
+            JDKToolLauncher launcher = JDKToolLauncher.createUsingTestJDK("javap");
+            launcher.addToolArg(APP_DOT_CLASSNAME);
+            System.out.println("> javap " + APP_DOT_CLASSNAME);
+            List<String> cmdStringList = Arrays.asList(launcher.getCommand());
+            ProcessBuilder pb = new ProcessBuilder(cmdStringList);
+            Process javap = pb.start();
+            OutputAnalyzer out = new OutputAnalyzer(javap);
+            javap.waitFor();
+            System.out.println(out.getStdout());
+            System.err.println(out.getStderr());
+            out.shouldHaveExitValue(0);
+            out.shouldMatch("public class " + APP_DOT_CLASSNAME);
+        } catch (SkippedException se) {
+            throw se;
+        } catch (Exception ex) {
+            throw new RuntimeException("Test ERROR " + ex, ex);
+        } finally {
+            LingeredApp.stopApp(theApp);
+        }
+        System.out.println("Test PASSED");
+    }
+}