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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package org.jboss.netty.util.internal;
17  
18  import java.security.AccessController;
19  import java.security.PrivilegedActionException;
20  import java.security.PrivilegedExceptionAction;
21  import java.util.concurrent.atomic.AtomicInteger;
22  import java.util.zip.Deflater;
23  
24  
25  /**
26   * Utility that detects various properties specific to the current runtime
27   * environment, such as Java version and the availability of the
28   * {@code sun.misc.Unsafe} object.
29   *
30   * <br>
31   * You can disable the use of {@code sun.misc.Unsafe} if you specify
32   * the System property <strong>org.jboss.netty.tryUnsafe</strong> with
33   * value of <code>false</code>. Default is <code>true</code>.
34   */
35  public final class DetectionUtil {
36  
37      private static final int JAVA_VERSION = javaVersion0();
38      private static final boolean HAS_UNSAFE = hasUnsafe(AtomicInteger.class.getClassLoader());
39      private static final boolean IS_WINDOWS;
40      static {
41          String os = System.getProperty("os.name").toLowerCase();
42          // windows
43          IS_WINDOWS =  os.indexOf("win") >= 0;
44      }
45  
46      /**
47       * Return <code>true</code> if the JVM is running on Windows
48       *
49       */
50      public static boolean isWindows() {
51          return IS_WINDOWS;
52      }
53  
54      public static boolean hasUnsafe() {
55          return HAS_UNSAFE;
56      }
57  
58      public static int javaVersion() {
59          return JAVA_VERSION;
60      }
61  
62      private static boolean hasUnsafe(ClassLoader loader) {
63          boolean useUnsafe = Boolean.valueOf(SystemPropertyUtil.get("org.jboss.netty.tryUnsafe", "true"));
64          if (!useUnsafe) {
65              return false;
66          }
67  
68          try {
69              Class<?> unsafeClazz = Class.forName("sun.misc.Unsafe", true, loader);
70              return hasUnsafeField(unsafeClazz);
71          } catch (Exception e) {
72              // Ignore
73          }
74          return false;
75      }
76  
77      private static boolean hasUnsafeField(final Class<?> unsafeClass) throws PrivilegedActionException {
78          return AccessController.doPrivileged(new PrivilegedExceptionAction<Boolean>() {
79              public Boolean run() throws Exception {
80                  unsafeClass.getDeclaredField("theUnsafe");
81                  return true;
82              }
83          });
84      }
85  
86      private static int javaVersion0() {
87          try {
88              // Check if its android, if so handle it the same way as java6.
89              //
90              // See https://github.com/netty/netty/issues/282
91              Class.forName("android.app.Application");
92              return 6;
93          } catch (ClassNotFoundException e) {
94              //Ignore
95          }
96  
97          try {
98              Deflater.class.getDeclaredField("SYNC_FLUSH");
99              return 7;
100         } catch (Exception e) {
101             // Ignore
102         }
103 
104         try {
105             Double.class.getDeclaredField("MIN_NORMAL");
106             return 6;
107         } catch (Exception e) {
108             // Ignore
109         }
110 
111         return 5;
112     }
113 
114     private DetectionUtil() {
115         // only static method supported
116     }
117 }