学习jvm，有必要学会自己编译一个jdk。《深入理解java虚拟机》里的“实战：自己编译JDK”用的是OpenJDK7,按照书本上的指导我没有编译成功。于是果断上官网 http://openjdk.java.net/ ，在Developers' Guide里有详细的获取源码的教程。

为了避免不必要的坑，当然不会在windows下玩。我的环境是：Ubuntu 16.04.1 LTS

首先：获取源码

OpenJDK的代码管理用的是Mercurial，如果有git或svn经验，其实差不多。（可能是作者写书那会网络还不是很好，现在的网络已经可以分分钟搞定了，所以建议clone下来）。

Mercurial的安装参照官网 https://www.mercurial-scm.org/wiki/Download。因为我有pip所以就直接pip install Mercurial。然后检查下是否安装成功。

$ hg version

# Output：
# Mercurial Distributed SCM (version 4.1)

按照手册上说：Mercurial安装好就可以clone了，除非你想提交代码，那需要配置~/.hgrc。现在只是学习源码，就免了。

A Mercurial installation is sufficient to clone a repository. Contributors who wish to submit changes will need some additional configuration as described below.

安装好以后就能直接下载代码了（熟悉git的能看到就是把git变成了hg）：

$ hg clone http://hg.openjdk.java.net/jdk9/dev 9dev

因为jdk是个森林(forest)，所以上一步我们clone的是主树(main tree)。

官网手册里可以hg tclone，可能我的Mercurial装的版本问题，没有tclone这个命令，不深究。

hg: unknown command 'tclone'
(did you mean clone?)

接下来需要使用get_source.sh来获取整个森林。

$ cd 9dev
$ sh ./get_source.sh

由于网络的原因，一开始我没全部clone下来。会有如下提醒信息(截取部分)：

                 ......

                  jdk:   transaction abort!
                  jdk:   rollback completed
                  jdk:   abort: stream ended unexpectedly (got 173 bytes, expected 327)

                  ......

WARNING: hotspot exited abnormally (255)
WARNING: jdk exited abnormally (255)
WARNING: nashorn exited abnormally (255)

我没有注意，直接make了。报了错才发现没有jdk这个目录，jdk根本没有下下来。

/bin/bash: line 0: cd: /happynewyear/jdksrc/9dev/jdk/make: No such file or directory
make/Main.gmk:81: recipe for target 'interim-cldrconverter' failed
make[2]: *** [interim-cldrconverter] Error 1

不停地试了很多遍才全部下载完成。

然后：编译

当你获得源码后，首先应该看的是README。里面有简单的介绍：

 Simple Build Instructions:
 
    0. Get the necessary system software/packages installed on your system, see
       http://hg.openjdk.java.net/jdk9/jdk9/raw-file/tip/README-builds.html
 
    1. If you don't have a jdk8 or newer jdk, download and install it from
       http://java.sun.com/javase/downloads/index.jsp
       Add the /bin directory of this installation to your PATH environment
       variable.
 
    2. Configure the build:
         bash ./configure
 
    3. Build the OpenJDK:
         make all
       The resulting JDK image should be found in build/*/images/jdk
 
  where make is GNU make 3.81 or newer, /usr/bin/make on Linux usually
  is 3.81 or newer. Note that on Solaris, GNU make is called "gmake".

Ant已经不需要了，ALT_*配置也不再支持。 所以书上的一大堆环境变量的配置，全部忽略。

    * Ant is no longer used when building the OpenJDK
    * Use of ALT_* environment variables for configuring the build is no longer
      supported

大胆的 bash ./configure，缺什么都会有提示。

比如需要jdk8或者9：

configure: Found potential Boot JDK using java(c) in PATH
configure: Potential Boot JDK found at /opt/jdk1.7.0_71 is incorrect JDK version (java version "1.7.0_71"); ignoring
configure: (Your Boot JDK must be version 8 or 9)
configure: Could not find a valid Boot JDK. You might be able to fix this by running 'sudo apt-get install openjdk-8-jdk'.
configure: This might be fixed by explicitly setting --with-boot-jdk
configure: error: Cannot continue
configure exiting with result code 1

比如需要 sudo apt-get install libx11-dev libxext-dev libxrender-dev libxtst-dev libxt-dev

configure: error: Could not find X11 libraries. You might be able to fix this by
running 'sudo apt-get install libx11-dev libxext-dev libxrender-dev libxtst-dev
libxt-dev'.
configure exiting with result code 1

比如需要 sudo apt-get install libcups2-dev

configure: error: Could not find cups! You might be able to fix this by running
'sudo apt-get install libcups2-dev'.
configure exiting with result code 1

比如需要 sudo apt-get install libfreetype6-dev

configure: error: Could not find freetype! You might be able to fix this by running 'sudo apt-get install libfreetype6-dev'.
configure exiting with result code 1 

比如需要 sudo apt-get install libasound2-dev

 configure: error: Could not find alsa! You might be able to fix this by running 'sudo apt-get install libasound2-dev'.
configure exiting with result code 1

当然，你可以在这之前都把所有的依赖安装好。

sudo apt-get install libx11-dev libxext-dev libxrender-dev libxtst-dev libxt-dev libcups2-dev libfreetype6-dev libasound2-dev

或者可以试试build-essential包（未验证，讲道理应该可以）：

$ sudo apt-get install build-essential

最后，所有的检查都通过以后，我们就可以进行make了。

make需要花点时间，耐性等待。成功后有如下提示：

Finished building target 'default (exploded-image)' in configuration 'linux-x86_64-normal-server-release'

 最后：测试

进入build目录，找到jdk，然后./java --version检查是否

cd  build/linux-x86_64-normal-server-release/jdk
./bin/java --version

得到如下输出：

openjdk 9-internal
OpenJDK Runtime Environment (build 9-internal+0-adhoc.wuyc.9dev)
OpenJDK 64-Bit Server VM (build 9-internal+0-adhoc.wuyc.9dev, mixed mode)

 可以看到自己的用户名，顺利完成作业。