开发者的自测利器-Hprof命令（寻找cpu热点）
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- 测试代码：
1 public class HProfTest { 2 public void slowMethod() { 3 try { 4 Thread.sleep(1000); 5 } catch (Exception e) { 6 e.printStackTrace(); 7 } 8 } 9 10 public void slowerMethod() { 11 try { 12 Thread.sleep(10000); 13 } catch (Exception e) { 14 e.printStackTrace(); 15 } 16 } 17 18 public static void main(String[] args) { 19 HProfTest test = new HProfTest(); 20 test.slowerMethod(); 21 test.slowMethod(); 22 } 23 }
- 影响性能点分析：
- 类中有两个方法，slowMethod（睡眠1秒，可以理解成该方法执行需要1秒）和slowerMethod(睡眠10秒，可以理解成该方法执行需要10秒)。
- 在程序中的方法执行的时间越长越影响性能，那么slowerMethod就是我们预期影响性能的方法，HProf命令究竟以什么形式展示这个影响性能的方法，请往下阅读。
-
hprof命令以及其参数介绍：/* times：java函数的执行时间 hprof=cpu是针对cpu统计时间 interval=10 采样10次 */ -agentlib:hprof=cpu=times,interval=10
- 使用方式：
- 点击run-->run configurations-->Java Application-->HProfTest-->选择Arguments选项卡-->在VM arguments框中填入参数
- 运行HProfTest
- 运行结果（会产生新文件java.hprof.txt）：
JAVA PROFILE 1.0.1, created Sat Sep 24 08:01:10 2016 Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: - Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. - Neither the name of Oracle nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Header for -agentlib:hprof (or -Xrunhprof) ASCII Output (JDK 5.0 JVMTI based) WARNING! This file format is under development, and is subject to change without notice. This file contains the following types of records: THREAD START THREAD END mark the lifetime of Java threads TRACE represents a Java stack trace. Each trace consists of a series of stack frames. Other records refer to TRACEs to identify (1) where object allocations have taken place, (2) the frames in which GC roots were found, and (3) frequently executed methods. HEAP DUMP is a complete snapshot of all live objects in the Java heap. Following distinctions are made: ROOT root set as determined by GC CLS classes OBJ instances ARR arrays SITES is a sorted list of allocation sites. This identifies the most heavily allocated object types, and the TRACE at which those allocations occurred. CPU SAMPLES is a statistical profile of program execution. The VM periodically samples all running threads, and assigns a quantum to active TRACEs in those threads. Entries in this record are TRACEs ranked by the percentage of total quanta they consumed; top-ranked TRACEs are typically hot spots in the program. CPU TIME is a profile of program execution obtained by measuring the time spent in individual methods (excluding the time spent in callees), as well as by counting the number of times each method is called. Entries in this record are TRACEs ranked by the percentage of total CPU time. The "count" field indicates the number of times each TRACE is invoked. MONITOR TIME is a profile of monitor contention obtained by measuring the time spent by a thread waiting to enter a monitor. Entries in this record are TRACEs ranked by the percentage of total monitor contention time and a brief description of the monitor. The "count" field indicates the number of times the monitor was contended at that TRACE. MONITOR DUMP is a complete snapshot of all the monitors and threads in the System. HEAP DUMP, SITES, CPU SAMPLES|TIME and MONITOR DUMP|TIME records are generated at program exit. They can also be obtained during program execution by typing Ctrl-\ (on Solaris) or by typing Ctrl-Break (on Win32). -------- THREAD START (obj=50000191, id = 200002, name="HPROF gc_finish watcher", group="system") THREAD START (obj=50000191, id = 200001, name="main", group="main") THREAD END (id = 200001) THREAD START (obj=50000191, id = 200003, name="DestroyJavaVM", group="main") THREAD END (id = 200003) TRACE 301758: HProfTest.slowerMethod(HProfTest.java:Unknown line) HProfTest.main(HProfTest.java:Unknown line) TRACE 301759: HProfTest.slowMethod(HProfTest.java:Unknown line) HProfTest.main(HProfTest.java:Unknown line) TRACE 301012: java.lang.AbstractStringBuilder.append(<Unknown Source>:Unknown line) java.lang.StringBuffer.append(<Unknown Source>:Unknown line) java.io.WinNTFileSystem.normalize(<Unknown Source>:Unknown line) java.io.WinNTFileSystem.normalize(<Unknown Source>:Unknown line) TRACE 300936: java.lang.AbstractStringBuilder.append(<Unknown Source>:Unknown line) java.lang.StringBuilder.append(<Unknown Source>:Unknown line) sun.net.www.ParseUtil.decode(<Unknown Source>:Unknown line) sun.misc.URLClassPath$JarLoader.<init>(<Unknown Source>:Unknown line) TRACE 301032: java.lang.CharacterDataLatin1.toLowerCase(<Unknown Source>:Unknown line) java.lang.Character.toLowerCase(<Unknown Source>:Unknown line) java.lang.String.toLowerCase(<Unknown Source>:Unknown line) java.io.WinNTFileSystem.hashCode(<Unknown Source>:Unknown line) TRACE 300937: java.lang.StringBuilder.append(<Unknown Source>:Unknown line) sun.net.www.ParseUtil.decode(<Unknown Source>:Unknown line) sun.misc.URLClassPath$JarLoader.<init>(<Unknown Source>:Unknown line) sun.misc.URLClassPath$3.run(<Unknown Source>:Unknown line) TRACE 300997: sun.net.www.ParseUtil.decode(<Unknown Source>:Unknown line) sun.misc.URLClassPath$JarLoader.<init>(<Unknown Source>:Unknown line) sun.misc.URLClassPath$3.run(<Unknown Source>:Unknown line) sun.misc.URLClassPath$3.run(<Unknown Source>:Unknown line) TRACE 300356: java.lang.Character.toUpperCase(<Unknown Source>:Unknown line) java.lang.Character.toUpperCase(<Unknown Source>:Unknown line) java.lang.ProcessEnvironment$NameComparator.compare(<Unknown Source>:Unknown line) java.lang.ProcessEnvironment$NameComparator.compare(<Unknown Source>:Unknown line) TRACE 300370: java.lang.ProcessEnvironment.<clinit>(<Unknown Source>:Unknown line) java.lang.System.getenv(<Unknown Source>:Unknown line) sun.usagetracker.UsageTrackerClient$2.run(<Unknown Source>:Unknown line) sun.usagetracker.UsageTrackerClient$2.run(<Unknown Source>:Unknown line) TRACE 300357: java.lang.Character.toUpperCase(<Unknown Source>:Unknown line) java.lang.ProcessEnvironment$NameComparator.compare(<Unknown Source>:Unknown line) java.lang.ProcessEnvironment$NameComparator.compare(<Unknown Source>:Unknown line) java.util.TreeMap.put(<Unknown Source>:Unknown line) TRACE 300338: java.lang.ProcessEnvironment$CheckedEntry.getKey(<Unknown Source>:Unknown line) java.util.AbstractMap.putAll(<Unknown Source>:Unknown line) java.util.TreeMap.putAll(<Unknown Source>:Unknown line) java.lang.ProcessEnvironment.<clinit>(<Unknown Source>:Unknown line) TRACE 301036: java.lang.String.toLowerCase(<Unknown Source>:Unknown line) java.io.WinNTFileSystem.hashCode(<Unknown Source>:Unknown line) java.io.File.hashCode(<Unknown Source>:Unknown line) java.util.HashMap.hash(<Unknown Source>:Unknown line) TRACE 301082: sun.misc.URLClassPath.getLoader(<Unknown Source>:Unknown line) sun.misc.URLClassPath.getNextLoader(<Unknown Source>:Unknown line) sun.misc.URLClassPath.getResource(<Unknown Source>:Unknown line) java.net.URLClassLoader$1.run(<Unknown Source>:Unknown line) CPU TIME (ms) BEGIN (total = 11076) Sat Sep 24 08:01:21 2016 rank self accum count trace method 1 90.29% 90.29% 1 301758 HProfTest.slowerMethod 2 9.03% 99.32% 1 301759 HProfTest.slowMethod 3 0.04% 99.36% 783 301012 java.lang.AbstractStringBuilder.append 4 0.03% 99.39% 665 300936 java.lang.AbstractStringBuilder.append 5 0.03% 99.41% 665 301032 java.lang.CharacterDataLatin1.toLowerCase 6 0.02% 99.43% 665 300937 java.lang.StringBuilder.append 7 0.02% 99.45% 12 300997 sun.net.www.ParseUtil.decode 8 0.02% 99.47% 398 300356 java.lang.Character.toUpperCase 9 0.02% 99.49% 1 300370 java.lang.ProcessEnvironment.<clinit> 10 0.02% 99.50% 388 300357 java.lang.Character.toUpperCase 11 0.02% 99.52% 42 300338 java.lang.ProcessEnvironment$CheckedEntry.getKey 12 0.02% 99.54% 12 301036 java.lang.String.toLowerCase 13 0.02% 99.56% 14 301082 sun.misc.URLClassPath.getLoader CPU TIME (ms) END - 结果分析：
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