解决方案：在android->sdk->build-tools-android-version 中有个 dx.bat
dx.bat --dex
命令的dx.bat脚本有这样一句代码
REM By default, give dx a max heap size of 1 gig and a stack size of 1meg.
rem This can be overridden by using "-JXmx..." and "-JXss..." options below.
set defaultXmx=-Xmx1024M
set defaultXss=-Xss1m
set defaultXmx=-Xmx1024M
原因就是此处设置的Xmx为1024M，编译打包APK时java虚拟机内存空间不足，修改为512M即可正常编译打包了。