The system is out of resources when building Apache FOP

When trying to build Apache FOP by ant on the command line, it complains:

[javac] The system is out of resources.
[javac] Consult the following stack trace for details.
[javac]     ...
[javac]     at com.sun.tools.javac.main.M开发者_运维知识库ain.compile(Main.java:353)

I don't understand. I have enough RAM, how can the system run out of resources?

You need to give more memory to your JVM. e.g. the below allocates 512Mb to the JVM.

javac -Xmx512m ...

The Java virtual machine runs with a fixed maximum memory size. For memory-intensive operations you need to increase this appropriately. -Xmx specifies the maximum amount of memory the JVM will take. -Xms specifies the amount of memory the JVM allocates on start-up.

There's a nice summary of options here.

Note: Given the above occurs via Ant, you may need to increase the memory available to Ant (e.g. set ANT_OPTS=-Xms256M -Xmx512M), and/or the memory available to your javac process if that's being forked as a separate executable.

the size of your system memory is only half of the story, the JVM allocates a memory chunck as a heap space when it starts up. the java compiler as a java application has only this amount of memory to work with

you can set the heap size for the java compiler yourself with this option

javac     -J-Xms<size>m 

see the complete switches sets here