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3.2 KiB

ja-netfilter 2022.2.0

A Java Instrumentation Framework


  • download from the releases page

  • add -javaagent:/absolute/path/to/ja-netfilter.jar argument (Change to your actual path)

    • add as an argument of the java command. eg: java -javaagent:/absolute/path/to/ja-netfilter.jar -jar executable_jar_file.jar
    • some apps support the JVM Options file, you can add as a line of the JVM Options file.
    • WARNING: DO NOT put some unnecessary whitespace characters!
  • or execute java -jar /path/to/ja-netfilter.jar to use attach mode.

  • for Java 17 you have to add at least these JVM Options:

  • edit your plugin config files: ${lower plugin name}.conf file in the config dir where ja-netfilter.jar is located.

  • the config, logs and plugins directories can be specified through the javaagent args.

    • eg: -javaagent:/path/to/ja-netfilter.jar=appName, your config, logs and plugins directories will be config-appname, logs-appname and plugins-appname.
    • if no javaagent args, they default to config, logs and plugins.
    • this mechanism will avoid extraneous and bloated config, logs and plugins.
  • run your java application and enjoy~

Config file format

# for the specified section name

# for example


# EQUAL       Use `equals` to compare
# EQUAL_IC    Use `equals` to compare, ignore case
# KEYWORD     Use `contains` to compare
# KEYWORD_IC  Use `contains` to compare, ignore case
# PREFIX      Use `startsWith` to compare
# PREFIX_IC   Use `startsWith` to compare, ignore case
# SUFFIX      Use `endsWith` to compare
# SUFFIX_IC   Use `endsWith` to compare, ignore case
# REGEXP      Use regular expressions to match

Debug info

  • the ja-netfilter will NOT output debugging information by default
  • add environment variable JANF_DEBUG=1 (log level) and start to enable it
  • or add system property -Djanf.debug=1 (log level) to enable it
  • log level: NONE=0, DEBUG=1, INFO=2, WARN=3, ERROR=4

Debug output

  • the ja-netfilter will output debugging information to the console by default
  • add environment variable JANF_OUTPUT=value and start to change output medium
  • or add system property -Djanf.output=value to change output medium
  • output medium value: [NONE=0, CONSOLE=1, FILE=2, CONSOLE+FILE=3, WITH_PID=4]
  • eg: console + file + pid file name = 1 + 2 + 4 = 7, so the -Djanf.output=7

Plugin system

  • for developer:

    • view the scaffold project written for the plugin system
    • compile your plugin and publish it
    • just use your imagination~
  • for user:

    • download the jar file of the plugin
    • put it in the subdirectory called plugins where the ja-netfilter.jar file is located
    • enjoy the new capabilities brought by the plugin
    • if the file suffix is .disabled.jar, the plugin will be disabled