[JDK工具-6] jmap java内存映射工具

jmap(Memory Map for Java)

1. 介绍

位置：jdk\bin

作用：

• jdk安装后会自带一些小工具，jmap命令(Memory Map for Java)是其中之一。主要用于打印指定Java进程(或核心文件、远程调试服务器)的共享对象内存映射或堆内存细节。

• jmap命令可以获得运行中的jvm的堆的快照，从而可以离线分析堆，以检查内存泄漏，检查一些严重影响性能的大对象的创建，检查系统中什么对象最多，各种对象所占内存的大小等等。可以使用jmap生成Heap Dump。

• 如果不想使用jmap命令，要想获取Java堆转储快照还有一些比较“暴力”的手段：譬如在前面用过的 -XX:+HeapDumpOnOutOfMemoryError参数，可以让虚拟机在OOM异常出现之后自动生成dump文件，通过-XX:+HeapDumpOnCtrlBreak参数可以使用[ctrl]+[Break]键让虚拟机生成dump文件，又或者在Linux系统下通过Kill -3 命令发送进程退出信息“恐吓”一下虚拟机，也能拿到dump文件。

• jmap的作用并不仅仅是为了获取dump文件，他还可以查询finalize执行队列，java堆和永久代的详细信息，如空间使用率、当前用的是哪种收集器等。

语法：

D:\javasoft\java_soft\jdk\bin>jmap
Usage:jmap [option] <pid>(to connect to running process)jmap [option] <executable <core>(to connect to a core file)jmap [option] [server_id@]<remote server IP or hostname>(to connect to remote debug server)where <option> is one of:<none>               to print same info as Solaris pmap-heap                to print java heap summary-histo[:live]        to print histogram of java object heap; if the "live"suboption is specified, only count live objects-clstats             to print class loader statistics-finalizerinfo       to print information on objects awaiting finalization-dump:<dump-options> to dump java heap in hprof binary formatdump-options:live         dump only live objects; if not specified,all objects in the heap are dumped.format=b     binary formatfile=<file>  dump heap to <file>Example: jmap -dump:live,format=b,file=heap.bin <pid>-F                   force. Use with -dump:<dump-options> <pid> or -histoto force a heap dump or histogram when <pid> does notrespond. The "live" suboption is not supportedin this mode.-h | -help           to print this help message-J<flag>             to pass <flag> directly to the runtime system

2. 主要选项

3. 生成java堆转储快照 jmap -dump

生成java对转存快照，格式：jmap -dump:[live,]format=b,file=文件名

可以使用jdk提供的jvisualvm.exe查看hprof文件

4. 显示堆详细信息 jmap -heap pid

D:\javasoft\java_soft\jdk\bin>jmap -heap 8644
Attaching to process ID 8644, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.271-b09using thread-local object allocation.
Parallel GC with 8 thread(s)Heap Configuration:MinHeapFreeRatio         = 0MaxHeapFreeRatio         = 100MaxHeapSize              = 1853882368 (1768.0MB)NewSize                  = 38797312 (37.0MB)MaxNewSize               = 617611264 (589.0MB)OldSize                  = 78643200 (75.0MB)NewRatio                 = 2SurvivorRatio            = 8MetaspaceSize            = 21807104 (20.796875MB)CompressedClassSpaceSize = 1073741824 (1024.0MB)MaxMetaspaceSize         = 17592186044415 MBG1HeapRegionSize         = 0 (0.0MB)Heap Usage:
PS Young Generation
Eden Space:capacity = 185597952 (177.0MB)used     = 1365920 (1.302642822265625MB)free     = 184232032 (175.69735717773438MB)0.7359563967602402% used
From Space:capacity = 16252928 (15.5MB)used     = 0 (0.0MB)free     = 16252928 (15.5MB)0.0% used
To Space:capacity = 18874368 (18.0MB)used     = 0 (0.0MB)free     = 18874368 (18.0MB)0.0% used
PS Old Generationcapacity = 101187584 (96.5MB)used     = 26049224 (24.84247589111328MB)free     = 75138360 (71.65752410888672MB)25.743498332759877% used21147 interned Strings occupying 2233672 bytes.

5. 显示堆中对象统计信息 jmap -histo pid

显示堆中对象统计信息，包括类、实例数量和合计容量

命令格式：jmap -histo[:live]

D:\javasoft\java_soft\jdk\bin>jps -l
10048 sun.tools.jps.Jps
13072 org/netbeans/Main
16212 com.xin.demo.threaddemo.bookdemo.DeadLockDemo
8644 com.xin.demo.XinJavaDemoApplication
5560
7016 org.jetbrains.jps.cmdline.Launcher
9544 com.xin.demo.threaddemo.bookdemo.OOMTestD:\javasoft\java_soft\jdk\bin>jmap -histo 9544num     #instances         #bytes  class name
----------------------------------------------1:          1066        1822048  [B2:          6646         978560  [C3:           390         186216  [I4:          6079         145896  java.lang.String5:           722          82784  java.lang.Class6:          1372          68968  [Ljava.lang.Object;7:           845          33800  java.util.LinkedHashMap$Entry8:           791          31640  java.util.TreeMap$Entry9:           783          25056  java.util.HashMap$Node10:           443          22376  [Ljava.lang.String;11:           305          19520  java.net.URL12:            57          16656  [Ljava.util.HashMap$Node;13:           406          16240  java.lang.ref.Finalizer14:           555          13320  java.util.LinkedList$Node15:           107          10272  java.util.jar.JarFile$JarFileEntry16:           123           9840  [Ljava.util.WeakHashMap$Entry;17:           286           9152  java.util.LinkedList18:           152           8512  sun.misc.URLClassPath$JarLoader19:           113           8136  java.lang.reflect.Field20:           120           7680  java.util.jar.JarFile21:           235           7520  java.util.Hashtable$Entry22:           123           6888  sun.nio.cs.UTF_8$Encoder23:           121           6776  java.util.zip.ZipFile$ZipFileInputStream24:           111           6216  java.util.zip.ZipFile$ZipFileInflaterInputStream25:           257           6168  java.io.ExpiringCache$Entry26:           123           5904  java.util.WeakHashMap27:           110           5280  java.util.zip.Inflater28:           121           4840  java.lang.ref.SoftReference29:           119           4760  sun.nio.cs.UTF_8$Decoder30:           130           4160  java.lang.ref.ReferenceQueue31:           256           4096  java.lang.Integer32:           120           3840  java.util.zip.ZipCoder33:           111           3552  java.util.concurrent.ConcurrentHashMap$Node34:           132           3168  java.lang.StringBuffer35:            22           3072  [Ljava.util.Hashtable$Entry;36:             8           3008  java.lang.Thread37:           120           2880  java.util.ArrayDeque38:            59           2832  java.util.HashMap39:           110           2640  java.util.zip.ZStreamRef40:             5           2600  [J41:           106           2544  java.lang.StringBuilder42:            30           2400  [S43:             2           2384  [[Ljava.lang.Object;44:           132           2112  java.lang.ref.ReferenceQueue$Lock45:            26           2080  java.lang.reflect.Constructor46:            16           2048  [Ljava.util.concurrent.ConcurrentHashMap$Node;47:            60           1920  java.io.File48:            39           1872  sun.util.locale.LocaleObjectCache$CacheEntry49:             1           1568  [[B50:            96           1536  java.lang.Object51:            37           1480  java.io.ObjectStreamField52:            26           1456  java.lang.Class$ReflectionData53:            20           1280  java.util.concurrent.ConcurrentHashMap54:             2           1064  [Ljava.lang.invoke.MethodHandle;55:             1           1040  [Ljava.lang.Integer;56:             1           1040  [[C57:            36            864  java.util.jar.Attributes$Name58:            21            840  sun.util.locale.BaseLocale$Key59:            11            648  [Ljava.lang.reflect.Field;60:            19            608  java.util.Locale61:            19            608  sun.util.locale.BaseLocale62:            13            520  java.security.AccessControlContext63:            21            504  java.util.Locale$LocaleKey64:            10            480  java.util.Hashtable65:            12            480  java.util.WeakHashMap$Entry66:            18            432  sun.misc.MetaIndex67:            22            416  [Ljava.lang.Class;68:            10            400  java.io.FileDescriptor69:            13            392  [Ljava.io.ObjectStreamField;70:             1            384  com.intellij.rt.execution.application.AppMainV2$171:             1            384  java.lang.ref.Finalizer$FinalizerThread72:            16            384  java.net.Parts73:             6            384  java.nio.DirectByteBuffer74:            16            384  java.util.ArrayList75:             1            376  java.lang.ref.Reference$ReferenceHandler76:             6            336  java.nio.DirectLongBufferU77:             7            336  java.nio.HeapCharBuffer78:             6            336  java.util.LinkedHashMap79:            10            320  java.lang.OutOfMemoryError80:             3            312  [D81:            13            312  [Ljava.lang.reflect.Constructor;82:            13            312  sun.reflect.NativeConstructorAccessorImpl83:             6            288  java.nio.HeapByteBuffer84:             6            288  java.util.Properties85:             3            280  [[Ljava.lang.String;86:             5            280  java.util.ResourceBundle$CacheKey87:             5            280  sun.util.calendar.ZoneInfo88:             3            264  java.lang.reflect.Method89:            11            264  java.net.StandardSocketOptions$StdSocketOption90:             8            256  java.util.Vector91:             3            240  [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry;92:             5            240  java.util.Hashtable$Enumerator93:             7            224  java.nio.file.attribute.FileTime94:             9            216  sun.misc.JarIndex95:            13            208  sun.reflect.DelegatingConstructorAccessorImpl96:             5            200  java.security.ProtectionDomain97:             6            192  java.io.FileInputStream98:             6            192  java.lang.ThreadLocal$ThreadLocalMap$Entry99:             4            192  java.util.TreeMap100:             8            192  sun.misc.URLClassPath$3101:             4            192  sun.nio.cs.StreamEncoder102:             3            192  sun.nio.cs.ext.DoubleByte$Encoder103:             2            192  sun.util.calendar.Gregorian$Date104:             4            160  java.io.BufferedWriter105:             4            160  java.lang.ClassLoader$NativeLibrary106:             5            160  java.security.CodeSource107:             4            160  java.security.PrivilegedActionException108:             5            160  java.util.ResourceBundle$LoaderReference109:             5            160  sun.util.locale.provider.LocaleProviderAdapter$Type110:             6            144  sun.misc.PerfCounter111:             3            144  sun.misc.URLClassPath112:             2            128  java.io.ExpiringCache$1113:             4            128  java.lang.StringCoding$StringEncoder114:             8            128  java.util.HashSet115:             4            128  java.util.Stack116:             1            120  java.net.SocksSocketImpl117:             5            120  java.util.Collections$UnmodifiableRandomAccessList118:             5            120  sun.misc.FloatingDecimal$PreparedASCIIToBinaryBuffer119:             2            112  java.lang.Package120:             2            112  sun.nio.cs.ISO_8859_1$Encoder121:             2            112  sun.nio.cs.ext.DoubleByte$Decoder122:             2             96  java.io.BufferedReader123:             3             96  java.io.FileOutputStream124:             4             96  java.io.OutputStreamWriter125:             4             96  java.lang.RuntimePermission126:             3             96  java.lang.StringCoding$StringDecoder127:             2             96  java.lang.ThreadGroup128:             6             96  java.lang.ThreadLocal129:             3             96  java.lang.ref.WeakReference130:             1             96  java.net.DualStackPlainSocketImpl131:             2             96  java.util.ResourceBundle$BundleReference132:             6             96  java.util.jar.Attributes133:             4             96  jdk.net.ExtendedSocketOptions$ExtSocketOption134:             1             96  sun.misc.Launcher$AppClassLoader135:             3             96  sun.net.spi.DefaultProxySelector$NonProxyInfo136:             2             96  sun.nio.cs.StreamDecoder137:             4             96  sun.security.action.GetPropertyAction138:             1             88  java.util.jar.JarVerifier139:             1             88  sun.misc.Launcher$ExtClassLoader140:             5             80  [Ljava.security.Principal;141:             2             80  [Lsun.util.locale.provider.LocaleProviderAdapter$Type;142:             2             80  java.io.BufferedInputStream143:             2             80  java.io.ExpiringCache144:             5             80  java.security.ProtectionDomain$Key145:             2             80  java.util.ServiceLoader$LazyIterator146:             2             80  sun.misc.FloatingDecimal$BinaryToASCIIBuffer147:             2             80  sun.misc.URLClassPath$1148:             2             80  sun.misc.URLClassPath$2149:             2             80  sun.util.locale.LanguageTag150:             3             72  java.io.ByteArrayOutputStream151:             3             72  java.lang.ThreadLocal$ThreadLocalMap152:             3             72  java.net.Proxy$Type153:             3             72  java.util.Arrays$ArrayList154:             3             72  java.util.Collections$SynchronizedSet155:             1             72  java.util.ResourceBundle$RBClassLoader156:             3             72  java.util.concurrent.atomic.AtomicLong157:             3             72  sun.misc.FloatingDecimal$ExceptionalBinaryToASCIIBuffer158:             1             72  sun.util.locale.provider.JRELocaleProviderAdapter159:             1             64  [F160:             2             64  [Ljava.lang.Thread;161:             2             64  java.io.DataInputStream162:             2             64  java.io.FileNotFoundException163:             2             64  java.io.FilePermission164:             2             64  java.io.PrintStream165:             2             64  java.lang.ClassValue$Entry166:             2             64  java.lang.VirtualMachineError167:             2             64  java.lang.ref.ReferenceQueue$Null168:             2             64  java.security.BasicPermissionCollection169:             2             64  java.security.Permissions170:             2             64  java.util.ArrayList$Itr171:             2             64  java.util.LinkedHashMap$LinkedEntryIterator172:             2             64  java.util.ServiceLoader173:             1             48  [Ljava.io.File;174:             2             48  [Ljava.lang.reflect.Method;175:             1             48  [Ljava.net.URL;176:             2             48  [Ljava.util.Enumeration;177:             1             48  [Ljava.util.concurrent.TimeUnit;178:             2             48  java.io.BufferedOutputStream179:             2             48  java.io.File$PathStatus180:             2             48  java.io.FilePermissionCollection181:             2             48  java.lang.Class$1182:             2             48  java.net.InetAddress$Cache183:             2             48  java.net.InetAddress$Cache$Type184:             1             48  java.net.SocketInputStream185:             2             48  java.net.URLClassLoader$3186:             2             48  java.nio.charset.CoderResult187:             3             48  java.nio.charset.CodingErrorAction188:             3             48  java.util.Collections$UnmodifiableSet189:             2             48  java.util.Date190:             3             48  java.util.HashMap$KeySet191:             3             48  java.util.LinkedHashMap$LinkedKeySet192:             2             48  java.util.ServiceLoader$1193:             1             48  java.util.StringTokenizer194:             2             48  java.util.jar.Manifest195:             2             48  sun.misc.CompoundEnumeration196:             2             48  sun.misc.FileURLMapper197:             2             48  sun.misc.NativeSignalHandler198:             2             48  sun.misc.Signal199:             3             48  sun.net.www.protocol.jar.Handler200:             2             48  sun.nio.cs.Surrogate$Parser201:             1             48  sun.nio.cs.US_ASCII$Decoder202:             1             48  sun.util.locale.provider.LocaleResources$ResourceReference203:             1             48  sun.util.resources.TimeZoneNames204:             1             48  sun.util.resources.en.TimeZoneNames_en205:             1             40  java.util.ResourceBundle$1206:             1             40  sun.nio.cs.StandardCharsets$Aliases207:             1             40  sun.nio.cs.StandardCharsets$Cache208:             1             40  sun.nio.cs.StandardCharsets$Classes209:             1             40  sun.nio.cs.ext.ExtendedCharsets210:             1             32  [Ljava.lang.OutOfMemoryError;211:             2             32  [Ljava.lang.StackTraceElement;212:             1             32  [Ljava.lang.ThreadGroup;213:             1             32  [Ljava.net.Proxy$Type;214:             1             32  java.io.ByteArrayInputStream215:             2             32  java.io.FileInputStream$1216:             1             32  java.io.WinNTFileSystem217:             1             32  java.lang.ArithmeticException218:             2             32  java.lang.Boolean219:             2             32  java.lang.ClassLoader$2220:             1             32  java.lang.NullPointerException221:             1             32  java.net.InetAddress$InetAddressHolder222:             1             32  java.net.Socket223:             2             32  java.net.URLClassLoader$3$1224:             2             32  java.nio.ByteOrder225:             2             32  java.util.Hashtable$KeySet226:             2             32  java.util.LinkedHashMap$LinkedEntrySet227:             1             32  java.util.LinkedHashMap$LinkedKeyIterator228:             2             32  java.util.concurrent.atomic.AtomicInteger229:             1             32  java.util.concurrent.atomic.AtomicReferenceFieldUpdater$AtomicReferenceFieldUpdaterImpl230:             1             32  jdk.net.ExtendedSocketOptions$1231:             1             32  sun.instrument.InstrumentationImpl232:             2             32  sun.misc.URLClassPath$JarLoader$1233:             1             32  sun.nio.cs.StandardCharsets234:             1             32  sun.util.locale.provider.LocaleResources235:             1             32  sun.util.locale.provider.LocaleServiceProviderPool236:             1             24  [Ljava.io.File$PathStatus;237:             1             24  [Ljava.lang.ClassValue$Entry;238:             1             24  [Ljava.net.InetAddress$Cache$Type;239:             1             24  [Ljava.security.ProtectionDomain;240:             1             24  [Lsun.launcher.LauncherHelper;241:             1             24  java.io.FileReader242:             1             24  java.io.InputStreamReader243:             1             24  java.lang.ClassValue$Version244:             1             24  java.lang.invoke.MethodHandleImpl$4245:             1             24  java.lang.reflect.ReflectPermission246:             1             24  java.net.Inet4Address247:             1             24  java.net.Inet6AddressImpl248:             1             24  java.net.Proxy249:             1             24  java.util.BitSet250:             1             24  java.util.Collections$EmptyMap251:             1             24  java.util.Collections$SetFromMap252:             1             24  java.util.Collections$UnmodifiableCollection$1253:             1             24  java.util.Locale$Cache254:             1             24  java.util.ResourceBundle$Control$CandidateListCache255:             1             24  java.util.concurrent.TimeUnit$1256:             1             24  java.util.concurrent.TimeUnit$2257:             1             24  java.util.concurrent.TimeUnit$3258:             1             24  java.util.concurrent.TimeUnit$4259:             1             24  java.util.concurrent.TimeUnit$5260:             1             24  java.util.concurrent.TimeUnit$6261:             1             24  java.util.concurrent.TimeUnit$7262:             1             24  sun.instrument.TransformerManager263:             1             24  sun.launcher.LauncherHelper264:             1             24  sun.misc.URLClassPath$FileLoader265:             1             24  sun.nio.cs.ISO_8859_1266:             1             24  sun.nio.cs.ThreadLocalCoders$1267:             1             24  sun.nio.cs.ThreadLocalCoders$2268:             1             24  sun.nio.cs.US_ASCII269:             1             24  sun.nio.cs.UTF_16270:             1             24  sun.nio.cs.UTF_16BE271:             1             24  sun.nio.cs.UTF_16LE272:             1             24  sun.nio.cs.UTF_8273:             1             24  sun.nio.cs.ext.GBK274:             1             24  sun.reflect.NativeMethodAccessorImpl275:             1             24  sun.util.locale.BaseLocale$Cache276:             1             24  sun.util.locale.provider.SPILocaleProviderAdapter$1277:             1             24  sun.util.locale.provider.TimeZoneNameProviderImpl278:             1             24  sun.util.resources.LocaleData$1279:             1             16  [Ljava.lang.Throwable;280:             1             16  [Ljava.security.CodeSigner;281:             1             16  [Ljava.security.cert.Certificate;282:             1             16  [Lsun.instrument.TransformerManager$TransformerInfo;283:             1             16  [Lsun.util.calendar.ZoneInfoFile$ZoneOffsetTransitionRule;284:             1             16  java.io.FileDescriptor$1285:             1             16  java.lang.CharacterDataLatin1286:             1             16  java.lang.ClassValue$Identity287:             1             16  java.lang.Runtime288:             1             16  java.lang.String$CaseInsensitiveComparator289:             1             16  java.lang.System$2290:             1             16  java.lang.Terminator$1291:             1             16  java.lang.invoke.MemberName$Factory292:             1             16  java.lang.invoke.MethodHandleImpl$2293:             1             16  java.lang.invoke.MethodHandleImpl$3294:             1             16  java.lang.ref.Reference$1295:             1             16  java.lang.ref.Reference$Lock296:             1             16  java.lang.reflect.ReflectAccess297:             1             16  java.net.InetAddress$2298:             1             16  java.net.URLClassLoader$7299:             1             16  java.nio.Bits$1300:             1             16  java.nio.charset.CoderResult$1301:             1             16  java.nio.charset.CoderResult$2302:             1             16  java.security.ProtectionDomain$2303:             1             16  java.security.ProtectionDomain$JavaSecurityAccessImpl304:             1             16  java.util.Collections$EmptyIterator305:             1             16  java.util.Collections$EmptyList306:             1             16  java.util.Collections$EmptySet307:             1             16  java.util.Hashtable$EntrySet308:             1             16  java.util.ResourceBundle$Control309:             1             16  java.util.ResourceBundle$RBClassLoader$1310:             1             16  java.util.TimeZone$1311:             1             16  java.util.WeakHashMap$KeySet312:             1             16  java.util.concurrent.atomic.AtomicBoolean313:             1             16  java.util.jar.JarVerifier$3314:             1             16  java.util.jar.JavaUtilJarAccessImpl315:             1             16  java.util.zip.ZipFile$1316:             1             16  jdk.net.ExtendedSocketOptions$PlatformSocketOptions317:             1             16  sun.misc.ASCIICaseInsensitiveComparator318:             1             16  sun.misc.FloatingDecimal$1319:             1             16  sun.misc.Launcher320:             1             16  sun.misc.Launcher$BootClassPathHolder$1321:             1             16  sun.misc.Launcher$Factory322:             1             16  sun.misc.Perf323:             1             16  sun.misc.Unsafe324:             1             16  sun.net.spi.DefaultProxySelector325:             1             16  sun.net.www.protocol.file.Handler326:             1             16  sun.reflect.DelegatingMethodAccessorImpl327:             1             16  sun.reflect.ReflectionFactory328:             1             16  sun.util.calendar.Gregorian329:             1             16  sun.util.calendar.ZoneInfoFile$1330:             1             16  sun.util.calendar.ZoneInfoFile$Checksum331:             1             16  sun.util.locale.provider.AuxLocaleProviderAdapter$NullProvider332:             1             16  sun.util.locale.provider.JRELocaleProviderAdapter$1333:             1             16  sun.util.locale.provider.SPILocaleProviderAdapter334:             1             16  sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter335:             1             16  sun.util.resources.LocaleData336:             1             16  sun.util.resources.LocaleData$LocaleDataResourceBundleControl
Total         25196        3662360