Java：尝试编译 Hadoop 程序时未找到 com.sun.tools.javac.Main
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Java: com.sun.tools.javac.Main not found when trying to compile Hadoop program
提问by Kudayar Pirimbaev
When I try to compile my program in Hadoop with this command
当我尝试使用此命令在 Hadoop 中编译我的程序时
bin/hadoop com.sun.tools.javac.Main WordCounter.java
from Hadoop folder, it says
从 Hadoop 文件夹，它说
Error: Could not find or load main class com.sun.tools.javac.Main
I looked in similar threads where people suggested to check if JAVA_HOMEis properly stated. So in etc/hadoop/hadoop-env.shI added this line
我查看了类似的线程，人们建议检查是否JAVA_HOME正确说明。所以在etc/hadoop/hadoop-env.sh我添加了这一行
export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64
then checked if tools.packis properly unpacked in /usr/lib/jvm/java-7-openjdk-amd64/liband it was. Then I tried javac -versionwhich gave
然后检查是否tools.pack已正确打开包装/usr/lib/jvm/java-7-openjdk-amd64/lib并且确实如此。然后我尝试了javac -version哪个给
javac 1.7.0_65
I tried to reinstall Java but it didn't solve the problem.
我尝试重新安装 Java，但没有解决问题。
回答by ponkin
Try to set HADOOP_CLASSPATHenvironment variable
尝试设置HADOOP_CLASSPATH环境变量
export HADOOP_CLASSPATH=$JAVA_HOME/lib/tools.jar
回答by Aaron Digulla
The error means you don't use a JDK to start Hadoop. The main difference between the JRE (pure runtime) and the JDK is the Java compiler javac. To see if you have a Java compiler, you need to check two places: There should be a javacin the $JAVA_HOME/binfolder plus there must be a file $JAVA_HOME/lib/tools.jar.
该错误意味着您没有使用 JDK 来启动 Hadoop。JRE（纯运行时）和 JDK 之间的主要区别在于 Java 编译器javac。要看到，如果你有一个Java编译器，你需要检查两个地方：应该有一个javac中$JAVA_HOME/bin文件夹加上必须有一个文件$JAVA_HOME/lib/tools.jar。
In your case, the first one (the binary to start the compiler) can be missing but you absolutely need the tools.jar.
在您的情况下，第一个（启动编译器的二进制文件）可能会丢失，但您绝对需要tools.jar.
You say that you have a tools.packbut I haven't heard about this one before. Use your package manager to search for openjdkand then look for a package in the result list which says jdk. On my system, that would be openjdk-7-jdk. Install this package and the error should go away.
你说你有一个，tools.pack但我以前没有听说过这个。使用您的包管理器搜索openjdk，然后在结果列表中查找显示jdk. 在我的系统上，那将是openjdk-7-jdk. 安装这个包，错误就会消失。
回答by William Laszlo
I had to downgrade Hadoop to 2.9.2 and it's working.
我不得不将 Hadoop 降级到 2.9.2 并且它正在工作。
I also had these in my environment:
我的环境中也有这些：
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk
export PATH=${JAVA_HOME}/bin:${PATH}
export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar
