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一、工具介绍

  如果把java\bin目录配置到环境变量，在cmd输入jmap会有如下提示：

翻译：打印出某个java进程（使用pid）内存内的，所有‘对象’的情况（如：产生那些对象，及其数量）。

可以输出所有内存中对象的工具，甚至可以将VM 中的heap，以二进制输出成文本。

二、工具用法

      jmap [ option ] pid

       jmap [ option ] executable core        jmap [ option ] [server-id@]remote-hostname-or-IP 2.1)、options：  executable Java executable from which the core dump was produced. (可能是产生core dump的java可执行程序) core 将被打印信息的core dump文件 remote-hostname-or-IP 远程debug服务的主机名或ip server-id 唯一id,假如一台主机上多个远程debug服务  2.2、基本参数： -dump:[live,]format=b,file=<filename> 使用hprof二进制形式,输出jvm的heap内容到文件=. live子选项是可选的，假如指定live选项,那么只输出活的对象到文件.  -finalizerinfo 打印正等候回收的对象的信息. -heap 打印heap的概要信息，GC使用的算法，heap的配置及wise heap的使用情况. -histo[:live] 打印每个class的实例数目,内存占用,类全名信息. VM的内部类名字开头会加上前缀”*”. 如果live子参数加上后,只统计活的对象数量.  -permstat 打印classload和jvm heap长久层的信息. 包含每个classloader的名字,活泼性,地址,父classloader和加载的class数量. 另外,内部String的数量和占用内存数也会打印出来.  -F 强迫.在pid没有相应的时候使用-dump或者-histo参数. 在这个模式下,live子参数无效.  -h | -help 打印辅助信息  -J 传递参数给jmap启动的jvm.  pid 需要被打印配相信息的java进程id,创业与打工的区别 - 博文预览,可以用jps查问.

三、测试代码

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.lang.management.ManagementFactory;public class JMapStudy {	public static void main(String[] args) {		//Gets the currentProcess's name		String name = ManagementFactory.getRuntimeMXBean().getName();				//result Format:16756@WIN--20141018KO		String pid = name.split("@")[0];		String command = "tasklist /fi \"pid eq " + pid + "\"";		executeCmd(command);		new JMapThread().start();		command = "jmap -histo " + pid;		executeCmd(command);	}	/**	 * Executes the special command by means of runtime, and output the result	 * to console	 * 	 * @param command	 */	public static void executeCmd(String command) {		try {			String s;			Process process = Runtime.getRuntime().exec(command);			BufferedReader bufferedReader =			new BufferedReader(new InputStreamReader(process.getInputStream()));			while ((s = bufferedReader.readLine()) != null)				System.out.println(s);			process.waitFor();		} catch (InterruptedException e) {			e.printStackTrace();		} catch (IOException e) {			e.printStackTrace();		}	}}class JMapThread extends Thread{	/**	 * This method is used for creating a process to be tested memory.	 */	public void run() {		for (int i = 0; i < 10; i++) {			try {				Thread.sleep(2000);			} catch (InterruptedException e) {				e.printStackTrace();			}			System.out.println("now i :" + i);		}	}}

四、运行结果

映像名称                       PID 会话名              会话#       内存使用 ========================= ======== ================ =========== ============javaw.exe                    12928 Console                    1     13,864 Know i :0now i :1now i :2 num     #instances         #bytes  class name----------------------------------------------   1:          1518         280472  [C   2:          1020         182192  
   
       3:           107         110032  [B   4:            30          96184  [I   5:          1398          33552  java.lang.String   6:           259          27200  
    
        7:           774          24768  java.util.TreeMap$Entry   8:           259          20976  
     
         9:            21          15344  
      
         10:           332          14280  [Ljava.lang.Object;  11:            39          12792  
       
          12:            21           8864  
        
          13: 21 6440 
         
           14: 192 6128 [Ljava.lang.String; 15: 76 6080 java.lang.reflect.Method 16: 60 5760 java.lang.Class 17: 103 4944 java.nio.HeapCharBuffer 18: 47 3968 [S 19: 60 2880 java.nio.HeapByteBuffer 20: 40 2880 java.lang.reflect.Field 21: 115 2288 [Ljava.lang.Class; 22: 23 2096 [Ljava.util.HashMap$Entry; 23: 51 2088 [[I 24: 83 1992 java.util.Hashtable$Entry 25: 13 1400 [Ljava.util.Hashtable$Entry; 26: 83 1328 java.lang.StringBuilder 27: 53 1272 java.util.HashMap$Entry 28: 32 1024 java.util.concurrent.ConcurrentHashMap$Segment 29: 15 840 java.net.URL 30: 32 768 java.util.concurrent.locks.ReentrantLock$NonfairSync 31: 35 752 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry; 32: 45 720 java.io.File 33: 10 640 java.lang.reflect.Constructor 34: 16 640 java.util.HashMap 35: 19 608 java.util.LinkedHashMap$Entry 36: 19 608 java.util.Locale 37: 18 576 java.lang.ref.Finalizer 38: 36 576 java.lang.ProcessEnvironment$CheckedEntry 39: 5 520 java.lang.Thread 40: 20 480 java.util.concurrent.ConcurrentHashMap$HashEntry 41: 14 448 java.lang.ref.SoftReference 42: 7 392 sun.nio.cs.ext.GBK$Decoder 43: 21 336 java.lang.StringBuffer 44: 10 320 java.io.ObjectStreamField 45: 2 320 [Ljava.lang.reflect.Method; 46: 13 312 java.io.ExpiringCache$Entry 47: 13 312 java.io.FileDescriptor 48: 17 272 sun.security.action.GetPropertyAction 49: 11 264 java.net.Parts 50: 10 240 java.security.AccessControlContext 51: 5 240 java.util.TreeMap 52: 6 240 java.util.Hashtable 53: 9 216 java.util.ArrayList 54: 5 200 sun.misc.URLClassPath$JarLoader 55: 4 184 [Ljava.lang.reflect.Field; 56: 7 168 java.util.Vector 57: 3 168 sun.nio.cs.ext.GBK$Encoder 58: 2 160 [Ljava.util.concurrent.ConcurrentHashMap$Segment; 59: 4 160 java.util.StringTokenizer 60: 8 152 [Ljava.io.ObjectStreamField; 61: 3 144 java.io.BufferedReader 62: 9 144 java.io.FileInputStream 63: 4 128 java.io.BufferedInputStream 64: 5 120 sun.reflect.NativeConstructorAccessorImpl 65: 3 120 sun.nio.cs.StreamDecoder 66: 2 112 java.io.ExpiringCache$1 67: 1 104 JMapThread 68: 1 104 java.lang.ref.Finalizer$FinalizerThread 69: 13 104 java.lang.Object 70: 1 104 java.lang.ref.Reference$ReferenceHandler 71: 2 96 java.net.Inet6Address 72: 1 96 sun.net.www.protocol.file.FileURLConnection 73: 2 96 sun.nio.cs.StreamEncoder 74: 3 96 java.lang.ClassLoader$NativeLibrary 75: 4 96 java.io.FileOutputStream 76: 6 96 sun.misc.URLClassPath$3 77: 2 96 java.lang.ThreadGroup 78: 4 96 java.lang.OutOfMemoryError 79: 2 96 java.util.Properties 80: 2 96 java.util.LinkedHashMap 81: 4 96 java.io.BufferedOutputStream 82: 5 80 [Ljava.lang.reflect.Constructor; 83: 5 80 java.lang.Boolean 84: 5 80 sun.misc.MetaIndex 85: 1 80 [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry; 86: 5 80 sun.reflect.DelegatingConstructorAccessorImpl 87: 2 80 java.util.concurrent.ConcurrentHashMap 88: 2 80 java.io.BufferedWriter 89: 2 80 java.lang.ProcessImpl 90: 5 80 java.lang.Class$1 91: 3 72 java.util.Stack 92: 3 72 java.lang.RuntimePermission 93: 3 72 java.lang.ref.WeakReference 94: 3 72 java.lang.NoSuchMethodError 95: 1 72 sun.misc.Launcher$AppClassLoader 96: 1 72 sun.misc.Launcher$ExtClassLoader 97: 3 72 sun.nio.cs.Surrogate$Parser 98: 2 64 java.lang.ClassNotFoundException 99: 2 64 java.io.PrintStream 100: 2 64 sun.misc.URLClassPath$FileLoader$1 101: 2 64 java.io.FilePermission 102: 2 64 [Ljava.lang.Thread; 103: 4 64 java.lang.Integer 104: 2 64 java.security.CodeSource 105: 2 64 java.lang.ThreadLocal$ThreadLocalMap$Entry 106: 4 64 java.net.URLClassLoader$1 107: 1 64 java.util.regex.Pattern 108: 2 64 java.util.LinkedHashMap$KeyIterator 109: 2 64 sun.misc.URLClassPath 110: 2 64 java.security.PrivilegedActionException 111: 2 64 java.util.LinkedList$ListItr 112: 2 64 java.io.ExpiringCache 113: 1 64 java.util.regex.Matcher 114: 1 56 [Ljava.util.regex.Pattern$GroupHead; 115: 3 56 [Ljava.io.File; 116: 3 48 java.lang.ThreadLocal 117: 2 48 java.lang.ref.ReferenceQueue 118: 2 48 [Ljava.net.URL; 119: 3 48 java.lang.ClassLoader$3 120: 1 48 [J 121: 2 48 java.lang.ProcessBuilder 122: 3 48 java.nio.charset.CodingErrorAction 123: 2 48 java.net.InetAddress$CacheEntry 124: 2 48 java.util.LinkedList$Entry 125: 2 48 java.security.Permissions 126: 2 48 java.lang.ref.ReferenceQueue$Null 127: 2 48 java.util.LinkedList 128: 2 48 java.net.Inet4Address 129: 2 48 java.lang.management.ManagementPermission 130: 2 48 java.io.InputStreamReader 131: 2 48 java.io.OutputStreamWriter 132: 1 40 java.lang.ProcessEnvironment 133: 1 40 sun.nio.cs.StandardCharsets$Classes 134: 1 40 sun.nio.cs.StandardCharsets$Cache 135: 1 40 java.util.Properties$LineReader 136: 2 40 [Ljava.net.InetAddress; 137: 5 40 java.lang.Class$3 138: 1 40 sun.nio.cs.StandardCharsets$Aliases 139: 1 32 java.security.ProtectionDomain 140: 2 32 java.nio.charset.CoderResult 141: 2 32 sun.security.action.LoadLibraryAction 142: 1 32 sun.misc.SoftCache 143: 2 32 sun.misc.Signal 144: 1 32 sun.nio.cs.ext.ExtendedCharsets 145: 2 32 java.lang.ProcessImpl$1 146: 1 32 java.util.Collections$SynchronizedMap 147: 2 32 java.nio.ByteOrder 148: 4 32 java.lang.ref.ReferenceQueue$Lock 149: 2 32 java.util.HashSet 150: 1 32 [Ljava.lang.ThreadGroup; 151: 2 32 java.net.InetAddress$Cache 152: 2 32 java.io.FilePermission$1 153: 1 32 java.util.RandomAccessSubList 154: 2 32 java.net.InetAddress$Cache$Type 155: 1 32 java.util.AbstractList$ListItr 156: 2 32 sun.misc.NativeSignalHandler 157: 1 32 [Ljava.lang.OutOfMemoryError; 158: 1 32 java.util.HashMap$EntryIterator 159: 1 32 java.util.concurrent.atomic.AtomicReferenceFieldUpdater$AtomicReferenceFieldUpdaterImpl 160: 4 32 sun.reflect.ReflectionFactory$GetReflectionFactoryAction 161: 1 24 sun.management.VMManagementImpl 162: 1 24 java.security.BasicPermissionCollection 163: 1 24 java.lang.StringCoding$StringDecoder 164: 1 24 sun.misc.Launcher$AppClassLoader$1 165: 1 24 java.io.WinNTFileSystem 166: 1 24 java.lang.reflect.ReflectPermission 167: 1 24 [Ljava.net.InetAddress$Cache$Type; 168: 3 24 sun.reflect.ReflectionFactory$1 169: 1 24 java.util.regex.Pattern$TreeInfo 170: 1 24 java.lang.NumberFormatException 171: 1 24 sun.security.action.GetIntegerAction 172: 1 24 sun.nio.cs.StandardCharsets 173: 1 24 java.util.SubList$1 174: 1 24 java.lang.ThreadLocal$ThreadLocalMap 175: 1 24 sun.nio.cs.ext.GBK 176: 1 24 java.lang.StringCoding$StringEncoder 177: 1 24 sun.management.RuntimeImpl 178: 1 24 java.util.BitSet 179: 1 24 sun.net.www.MessageHeader 180: 1 24 java.io.FileReader 181: 1 24 java.lang.ref.Reference 182: 1 24 java.util.Collections$UnmodifiableMap 183: 1 16 sun.misc.Launcher$ExtClassLoader$1 184: 1 16 [Ljava.security.Principal; 185: 1 16 java.lang.SystemClassLoaderAction 186: 1 16 java.security.ProtectionDomain$Key 187: 1 16 java.security.Policy$UnsupportedEmptyCollection 188: 1 16 java.util.HashMap$EntrySet 189: 1 16 sun.security.action.GetBooleanAction 190: 1 16 java.io.FilePermissionCollection 191: 1 16 [Ljava.lang.StackTraceElement; 192: 2 16 sun.net.www.protocol.jar.Handler 193: 1 16 java.util.regex.Pattern$5 194: 1 16 java.util.regex.Pattern$Start 195: 1 16 java.util.regex.Pattern$Single 196: 1 16 java.util.concurrent.atomic.AtomicInteger 197: 1 16 java.util.regex.Pattern$Node 198: 1 16 sun.misc.Launcher 199: 1 16 sun.misc.URLClassPath$FileLoader 200: 1 16 java.util.regex.Pattern$LastNode 201: 1 16 java.util.HashMap$KeySet 202: 1 16 java.util.Collections$EmptyMap 203: 1 16 [Ljava.security.cert.Certificate; 204: 1 16 java.nio.charset.CoderResult$1 205: 1 16 java.lang.ProcessEnvironment$CheckedEntrySet 206: 1 16 java.util.Collections$EmptyList 207: 1 16 java.nio.charset.CoderResult$2 208: 1 16 java.net.Inet6AddressImpl 209: 1 16 sun.jkernel.DownloadManager$1 210: 1 16 java.net.Inet4AddressImpl 211: 1 16 [Ljava.security.ProtectionDomain; 212: 1 16 java.lang.ProcessEnvironment$CheckedEntrySet$1 213: 1 8 sun.net.www.protocol.file.Handler 214: 1 8 java.net.InetAddress$1 215: 1 8 sun.misc.Unsafe 216: 1 8 java.util.Collections$EmptySet 217: 1 8 java.net.InetAddressImplFactory 218: 1 8 java.lang.ref.Reference$Lock 219: 1 8 java.util.Collections$ReverseComparator 220: 1 8 sun.net.InetAddressCachePolicy$2 221: 1 8 sun.misc.Launcher$Factory 222: 1 8 sun.jkernel.DownloadManager$2 223: 1 8 java.lang.ProcessEnvironment$NameComparator 224: 1 8 java.lang.ProcessEnvironment$EntryComparator 225: 1 8 java.util.Hashtable$EmptyEnumerator 226: 1 8 java.lang.Compiler$1 227: 1 8 java.lang.Terminator$1 228: 1 8 java.nio.charset.Charset$3 229: 1 8 java.lang.System$2 230: 1 8 java.lang.Runtime 231: 1 8 java.net.UnknownContentHandler 232: 1 8 sun.misc.ASCIICaseInsensitiveComparator 233: 1 8 java.net.URLClassLoader$7 234: 1 8 java.lang.reflect.ReflectAccess 235: 1 8 java.security.ProtectionDomain$2 236: 1 8 sun.reflect.ReflectionFactory 237: 1 8 sun.net.InetAddressCachePolicy$1 238: 1 8 java.util.Hashtable$EmptyIterator 239: 1 8 java.security.Security$1 240: 1 8 java.lang.String$CaseInsensitiveComparatorTotal 7599 899640now i :3now i :4now i :5now i :6now i :7now i :8now i :9
         
        
       
      
     
    
   

相关链接：

http://blog.csdn.net/fenglibing/article/details/6411953

http://blog.csdn.net/zhaozheng7758/article/details/8623530