ubuntu Cannot find System Java Compiler. Ensure that you have installed a JDK (not just a JRE)

1、Install JDK
sudo apt-get install openjdk-7-jdk
2、Make your $JAVA_HOME point to the newly installed JDK
echo $JAVA_HOME
# prints nothing

sudo echo 'JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64' >> /etc/profile
source /etc/profile

echo $JAVA_HOME
# /usr/lib/jvm/java-7-openjdk-amd64
3、Update your java command symlink
java -version
# java version "1.6.0_32"
# OpenJDK Runtime Environment (IcedTea6 1.13.4) (6b32-1.13.4-1~deb7u1)
# OpenJDK 64-Bit Server VM (build 23.25-b01, mixed mode)
which java
# /usr/bin/java
ls -l /usr/bin/java
# lrwxrwxrwx 1 root root 22 Sep 20 21:22 /usr/bin/java -> /etc/alternatives/java
ls -l /etc/alternatives/java
# lrwxrwxrwx 1 root root 42 Sep 21 00:01 /etc/alternatives/java -> /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java

sudo rm /etc/alternatives/java
sudo ln -s /usr/lib/jvm/java-7-openjdk-amd64/bin/java /etc/alternatives/java

java -version
# java version "1.7.0_65"
# OpenJDK Runtime Environment (IcedTea 2.5.1) (7u65-2.5.1-5~deb7u1)
# OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode)
4、Try again