#1519 fix NoClassDefFoundError on loading com/sun/management/UnixOper…

metrics-jvm/src/main/java/com/codahale/metrics/jvm/FileDescriptorRatioGauge.java

@@ -1,7 +1,6 @@
 package com.codahale.metrics.jvm;
 
 import com.codahale.metrics.RatioGauge;
-import com.sun.management.UnixOperatingSystemMXBean;
 
 import java.lang.management.ManagementFactory;
 import java.lang.management.OperatingSystemMXBean;
@@ -10,8 +9,19 @@
  * A gauge for the ratio of used to total file descriptors.
  */
 public class FileDescriptorRatioGauge extends RatioGauge {
+    private static boolean unixOperatingSystemMXBeanExists = false;
+
     private final OperatingSystemMXBean os;
 
+    static {
+        try {
+            Class.forName("com.sun.management.UnixOperatingSystemMXBean");
+            unixOperatingSystemMXBeanExists = true;
+        } catch (ClassNotFoundException e) {
+            // do nothing
+        }
+    }
+
     /**
      * Creates a new gauge using the platform OS bean.
      */
@@ -30,8 +40,8 @@ public FileDescriptorRatioGauge(OperatingSystemMXBean os) {
 
     @Override
     protected Ratio getRatio() {
-        if (os instanceof UnixOperatingSystemMXBean) {
-            final UnixOperatingSystemMXBean unixOs = (UnixOperatingSystemMXBean) os;
+        if (unixOperatingSystemMXBeanExists && os instanceof com.sun.management.UnixOperatingSystemMXBean) {
+            final com.sun.management.UnixOperatingSystemMXBean unixOs = (com.sun.management.UnixOperatingSystemMXBean) os;
             return Ratio.of(unixOs.getOpenFileDescriptorCount(), unixOs.getMaxFileDescriptorCount());
         } else {
             return Ratio.of(Double.NaN, Double.NaN);

metrics-jvm/src/test/java/com/codahale/metrics/jvm/FileDescriptorRatioGaugeSunManagementNotExistsTest.java

@@ -0,0 +1,117 @@
+package com.codahale.metrics.jvm;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.File;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.security.AccessController;
+import java.security.CodeSource;
+import java.security.PermissionCollection;
+import java.security.Permissions;
+import java.security.PrivilegedAction;
+import java.util.LinkedHashSet;
+import java.util.Set;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.BlockJUnit4ClassRunner;
+import org.junit.runners.model.InitializationError;
+
+@RunWith(FileDescriptorRatioGaugeSunManagementNotExistsTest.SunManagementNotExistsTestRunner.class)
+public class FileDescriptorRatioGaugeSunManagementNotExistsTest {
+
+    @Test
+    public void validateFileDescriptorRatioWhenSunManagementNotExists() {
+        assertThat(new FileDescriptorRatioGauge().getValue()).isNaN();
+    }
+
+    public static class SunManagementNotExistsTestRunner extends BlockJUnit4ClassRunner {
+
+        public SunManagementNotExistsTestRunner(Class<?> clazz) throws InitializationError {
+            super(getFromSunManagementNotExistsClassLoader(clazz));
+        }
+
+        private static Class<?> getFromSunManagementNotExistsClassLoader(Class<?> clazz) throws InitializationError {
+            try {
+                return Class.forName(clazz.getName(), true,
+                        new SunManagementNotExistsClassLoader(SunManagementNotExistsTestRunner.class.getClassLoader()));
+            } catch (ClassNotFoundException e) {
+                throw new InitializationError(e);
+            }
+        }
+    }
+
+    public static class SunManagementNotExistsClassLoader extends URLClassLoader {
+        private static final URL[] CLASSPATH_ENTRY_URLS;
+        private static final PermissionCollection NO_PERMS = new Permissions();
+
+        static {
+            String[] classpathEntries = AccessController.doPrivileged(new PrivilegedAction<String>() {
+                @Override
+                public String run() {
+                    return System.getProperty("java.class.path");
+                }
+            }).split(File.pathSeparator);
+            CLASSPATH_ENTRY_URLS = getClasspathEntryUrls(classpathEntries);
+        }
+
+        private static URL[] getClasspathEntryUrls(String... classpathEntries) {
+            Set<URL> classpathEntryUrls = new LinkedHashSet<>(classpathEntries.length, 1);
+            for (String classpathEntry : classpathEntries) {
+                URL classpathEntryUrl = getClasspathEntryUrl(classpathEntry);
+                if (classpathEntryUrl != null) {
+                    classpathEntryUrls.add(classpathEntryUrl);
+                }
+            }
+            return classpathEntryUrls.toArray(new URL[classpathEntryUrls.size()]);
+        }
+
+        private static URL getClasspathEntryUrl(String classpathEntry) {
+            try {
+                if (classpathEntry.endsWith(".jar")) {
+                    return new URL("file:jar:" + classpathEntry);
+                }
+                if (!classpathEntry.endsWith("/")) {
+                    classpathEntry = classpathEntry + "/";
+                }
+                return new URL("file:" + classpathEntry);
+            } catch (MalformedURLException mue) {
+                // do nothing
+            }
+            return null;
+        }
+
+        public SunManagementNotExistsClassLoader(ClassLoader parent) {
+            super(CLASSPATH_ENTRY_URLS, parent);
+        }
+
+        @Override
+        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+            if (getClass().getName().equals(name)) {
+                return getClass();
+            }
+            if (name.startsWith("com.sun.management.")) {
+                throw new ClassNotFoundException(name);
+            }
+            if (name.startsWith("com.codahale.metrics.jvm.")) {
+                return loadMetricsClasses(name);
+            }
+            return super.loadClass(name, resolve);
+        }
+
+        private Class<?> loadMetricsClasses(String name) throws ClassNotFoundException {
+            Class<?> ret = findLoadedClass(name);
+            if (ret != null) {
+                return ret;
+            }
+            return findClass(name);
+        }
+
+        @Override
+        protected PermissionCollection getPermissions(CodeSource codesource) {
+            return NO_PERMS;
+        }
+    }
+}