一、工具介绍
假设把javain文件夹配置到环境变量。在cmd输入jmap会有例如以下提示：
翻译：打印出某个java进程（使用pid）内存内的，全部‘对象’的情况（如：产生那些对象，及其数量）。
能够输出全部内存中对象的工具，甚至能够将VM 中的heap，以二进制输出成文本。
二、工具使用方法
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可运行程序)
core 将被信息打印的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、基本參数：
-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,那么仅仅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] 打印每一个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”*”. 假设live子參数加上后,仅仅统计活的对象数量.
-permstat 打印classload和jvm heap长久层的信息. 包括每一个classloader的名字,活泼性,地址,父classloader和载入的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没有对应的时候使用-dump或者-histo參数. 在这个模式下,live子參数无效.
-h | -help 打印辅助信息
-J 传递參数给jmap启动的jvm.
pid 须要被打印配相信息的java进程id,创业与打工的差别 - 博文预览,能够用jps查问.
三、測试代码
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、执行结果
映像名称 PID 会话名 会话# 内存使用 ========================= ======== ================ =========== ============ javaw.exe 12928 Console 1 13,864 K now i :0 now i :1 now i :2 num #instances #bytes class name ---------------------------------------------- 1: 1518 280472 [C 2: 1020 182192 <symbolKlass> 3: 107 110032 [B 4: 30 96184 [I 5: 1398 33552 java.lang.String 6: 259 27200 <constMethodKlass> 7: 774 24768 java.util.TreeMap$Entry 8: 259 20976 <methodKlass> 9: 21 15344 <constantPoolKlass> 10: 332 14280 [Ljava.lang.Object; 11: 39 12792 <objArrayKlassKlass> 12: 21 8864 <instanceKlassKlass> 13: 21 6440 <constantPoolCacheKlass> 14: 192 6128 [Ljava.lang.String; 15: 76 6080 java.lang.reflect.Method 16: 60 5760 java.lang.Class 17: 103 4944 java.nio.HeapCharBuffer 18: 47 3968 [S 19: 60 2880 java.nio.HeapByteBuffer 20: 40 2880 java.lang.reflect.Field 21: 115 2288 [Ljava.lang.Class; 22: 23 2096 [Ljava.util.HashMap$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$1 240: 1 8 java.lang.String$CaseInsensitiveComparator Total 7599 899640 now i :3 now i :4 now i :5 now i :6 now i :7 now i :8 now i :9
相关链接：
http://blog.csdn.net/fenglibing/article/details/6411953
http://blog.csdn.net/zhaozheng7758/article/details/8623530