开发者的自测利器-Hprof命令（寻找cpu热点）

1. 测试代码：

    public class HProfTest {
        public void slowMethod() {
            try {
                Thread.sleep(1000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
   
        public void slowerMethod() {
            try {
                Thread.sleep(10000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
   
        public static void main(String[] args) {
            HProfTest test = new HProfTest();
            test.slowerMethod();
            test.slowMethod();
        }
    }

2. 影响性能点分析：
   1. 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)。
   2. 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。

3. 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

4. 使用方式：
   1. 点击run-->run configurations-->Java Application-->HProfTest-->选择Arguments选项卡-->在VM arguments框中填入参数
   2. 运行HProfTest
5. 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
   

6. 结果分析：