在Gentoo中如果直接emerge jdk，会安装virtual/jdk这个包，默认依赖开源的dev-java/icedtea-bin；
如果直接emerge oracle-jdk-bin，则直接安装高版本的oracle-jdk-bin-1.8，同时也会安装icedtea-bin。
想直接用oracle-jdk-bin-1.7的话，不想安装icedtea-bin，并且不用mask掉高版本的oracle-jdk，可以这样来安装：
1、查找1.7的oracle-jdk具体版本
ls /usr/portage/dev-java/oracle-jdk-bin/
结果如下：
ChangeLog files oracle-jdk-bin-1.7.0.60.ebuild oracle-jdk-bin-1.7.0.72.ebuild Manifest metadata.xml oracle-jdk-bin-1.7.0.71.ebuild oracle-jdk-bin-1.8.0.25.ebuild
确定1.7的版本号为oracle-jdk-bin-1.7.0.72。
2、安装此版本的oracle-jdk
emerge -av =oracle-jdk-bin-1.7.0.72
出现如下提示：
These are the packages that would be merged, in order: Calculating dependencies... done! [ebuild RF ] dev-java/oracle-jdk-bin-1.7.0.72:1.7 USE="X alsa fontconfig (-aqua) -derby -doc -examples -jce -nsplugin -pax_kernel (-selinux) -source" 138,893 KiB Total: 1 package (1 reinstall), Size of downloads: 138,893 KiB Fetch Restriction: 1 package (1 unsatisfied) Fetch instructions for dev-java/oracle-jdk-bin-1.7.0.72: * * Oracle requires you to download the needed files manually after * accepting their license through a javascript capable web browser. * * Download the following files: * jdk-7u72-linux-x64.tar.gz * at 'http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html' * and move them to '/usr/portage/distfiles' * * If the above mentioned urls do not point to the correct version anymore, * please download the files from Oracle's java download archive: * * http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase7-521261.html#jdk-7u72-oth-JPR * Would you like to merge these packages? [Yes/No]
说明需要去oracle官网去下载“jdk-7u72-linux-x64.tar.gz”，去下面提示的“http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html”下载。前提是你要有oracle的帐号，登录之后，同意下载协议后就可以下载。下载之后，将文件复制到/usr/portage/distfiles/目录才可以安装。
3、最后再安装virtual/jdk
emerge -av jdk
你会发现不再安装icedtea-bin这个包了。
4、配置jdk
eselect java-vm list
出现：
Available Java Virtual Machines: [1] icedtea-bin-1.7 system-vm //注：好像是这样，记不清了，因为设置之后就没这个选项了 [2] oracle-jdk-bin-1.7
然后运行：
eselect java-vm set system 2
设置完成，查看一下：
eselect java-vm list
出现如下提示，说明设置正确了。
Available Java Virtual Machines: [1] oracle-jdk-bin-1.7 system-vm
5、设置JAVA_HOME、JDK_HOME
vi /etc/profile
将下面两行添加到文件末尾：
JAVA_HOME=/opt/oracle-jdk-bin-1.7.0.72 JDK_HOME=/opt/oracle-jdk-bin-1.7.0.72/bin
至此，整个安装配置过程完成。