常用到System.getProperty(), 而参数老不记得，这里贴一下，省得下次麻烦.
java.version | Java Runtime Environment version |
| java.vendor | Java Runtime Environment vendor |
| java.vendor.url | Java vendor URL |
| java.home | Java installation directory |
| java.vm.specification.version | Java Virtual Machine specification version |
| java.vm.specification.vendor | Java Virtual Machine specification vendor |
| java.vm.specification.name | Java Virtual Machine specification name |
| java.vm.version | Java Virtual Machine implementation version |
| java.vm.vendor | Java Virtual Machine implementation vendor |
| java.vm.name | Java Virtual Machine implementation name |
| java.specification.version | Java Runtime Environment specification version |
| java.specification.vendor | Java Runtime Environment specification vendor |
| java.specification.name | Java Runtime Environment specification name |
| java.class.version | Java class format version number |
| java.class.path | Java class path |
| java.library.path | List of paths to search when loading libraries |
| java.io.tmpdir | Default temp file path |
| java.compiler | Name of JIT compiler to use |
| java.ext.dirs | Path of extension directory or directories |
| os.name | Operating system name |
| os.arch | Operating system architecture |
| os.version | Operating system version |
| file.separator | File separator ("/" on UNIX) |
| path.separator | Path separator (":" on UNIX) |
| line.separator | Line separator ("\n" on UNIX) |
| user.name | User's account name |
| user.home | User's home directory |
| user.dir | User's current working directory |