Unable to find a javac compiler

In Tomcat, Jetty, or another servlet container, you may receive an error stating the javac compiler can't be found. The obvious reason is if you are running from a JRE and not a JDK, however, it can still happen even when running a JDK.

The following is a typical error message: <geshi> HTTP ERROR: 500

Unable to find a javac compiler; com.sun.tools.javac.Main is not on the classpath. Perhaps JAVA_HOME does not point to the JDK. It is currently set to "/java/jdk1.6.0_17/jre"

RequestURI=/web/ Caused by:

Unable to find a javac compiler; com.sun.tools.javac.Main is not on the classpath. Perhaps JAVA_HOME does not point to the JDK. It is currently set to "/app/java/jdk1.6.0_17/jre" at org.apache.tools.ant.taskdefs.compilers.CompilerAdapterFactory.getCompiler(CompilerAdapterFactory.java:108) at org.apache.tools.ant.taskdefs.Javac.compile(Javac.java:1058) at org.apache.tools.ant.taskdefs.Javac.execute(Javac.java:882) at org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:382) at org.apache.jasper.compiler.Compiler.compile(Compiler.java:472) at org.apache.jasper.compiler.Compiler.compile(Compiler.java:451) at org.apache.jasper.compiler.Compiler.compile(Compiler.java:439) at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:511) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:295) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:502) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:363) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:757) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:416) at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:334) at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:126) at org.mortbay.jetty.servlet.DefaultServlet.doGet(DefaultServlet.java:463) at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) </geshi>

You can verify the running JVM properties using the jinfo command. Example:

<geshi> /java/jdk1.6.0_17/bin/jinfo -sysprops 26314 | grep java.home Attaching to process ID 26314, please wait... Debugger attached successfully. Server compiler detected. JVM version is 14.3-b01 java.home = /java/jdk1.6.0_17/jre </geshi>

The easiest solution is to copy the tools.jar into the lib directory.

<geshi> cp -p /java/jdk1.6.0_17/lib/tools.jar /java/jdk1.6.0_17/jre/lib/ </geshi>

Alternatively, you can specify tools.jar on the classpath. For example: <geshi> $ /java/jdk1.6.0_17/bin/java -cp /java/jdk1.6.0_17/lib/tools.jar com.sun.tools.javac.Main Usage: javac <options> <source files> where possible options include:

 -g                         Generate all debugging info
 -g:none                    Generate no debugging info
 -g:{lines,vars,source}     Generate only some debugging info
 -nowarn                    Generate no warnings
 -verbose                   Output messages about what the compiler is doing
 -deprecation               Output source locations where deprecated APIs are used
 -classpath <path>          Specify where to find user class files and annotation processors
 -cp <path>                 Specify where to find user class files and annotation processors
 -sourcepath <path>         Specify where to find input source files
 -bootclasspath <path>      Override location of bootstrap class files
 -extdirs <dirs>            Override location of installed extensions
 -endorseddirs <dirs>       Override location of endorsed standards path
 -proc:{none,only}          Control whether annotation processing and/or compilation is done.
 -processor <class1>[,<class2>,<class3>...]Names of the annotation processors to run; bypasses default discovery process
 -processorpath <path>      Specify where to find annotation processors
 -d <directory>             Specify where to place generated class files
 -s <directory>             Specify where to place generated source files
 -implicit:{none,class}     Specify whether or not to generate class files for implicitly referenced files 
 -encoding <encoding>       Specify character encoding used by source files
 -source <release>          Provide source compatibility with specified release
 -target <release>          Generate class files for specific VM version
 -version                   Version information
 -help                      Print a synopsis of standard options
 -Akey[=value]              Options to pass to annotation processors
 -X                         Print a synopsis of nonstandard options
 -J<flag>                   Pass <flag> directly to the runtime system

</geshi>