Overview

What are we here to do today?

Learn about some useful and helpful JDK tools

Discover where to find more information about each of them

See a few of them in action

The Tools of the JDK

Build tools

jar - create an archive for classes and resources, and manipulate or restore individual classes or resources from an archive

jarsigner - sign and verify Java Archive (JAR) files

javac - read Java class and interface definitions and compile them into bytecode and class files

javadoc - generate HTML pages of API documentation from Java source files

jdeprscan - static analysis tool that scans for uses of deprecated API elements

jlink - assemble and optimize a set of modules and their dependencies into a custom runtime image

jmod - create JMOD files and list the content of existing JMOD files

keytool - manage a keystore (database) of cryptographic keys, X.509 certificate chains, and trusted certificates

serialver - return the serialVersionUID for one or more classes in a form suitable for copying into an evolving class

The Tools of the JDK

Run/Deploy tools

java - launch a Java application

jdeps - launch the Java class dependency analyzer

jpackage - package a self-contained Java application

jshell - interactively evaluate declarations, statements, and expressions of the Java programming language in a REPL

jrunscript - run a command-line script shell that supports interactive and batch modes

jwebserver - launch the Java Simple Web Server

rmiregistry - create and start a remote object registry on the specified port on the current host

The Tools of the JDK

Debug tools

javap - disassemble one or more class files

jdb - find and fix bugs in Java platform programs

jhsdb - attach to a Java process or launch a postmortem debugger to analyze the content of a core dump from a crashed JVM

jmap - print details of a specified process

jnativescan - static analysis tool that scans one or more jar files for uses of native functionalities

jstack - print Java stack traces of Java threads for a specified Java process

The Tools of the JDK

Observe tools

jcmd - send diagnostic command requests to a running Java Virtual Machine (JVM)

jconsole - start a graphical console to monitor and manage Java applications

jfr - parse and print Flight Recorder files

jinfo - generate Java configuration information for a specified Java process

jps - list the instrumented JVMs on the target system

jstat - monitor JVM statistics

jstatd - monitor the creation and termination of instrumented Java HotSpot VMs

jar

Overview

https://docs.oracle.com/en/java/javase/17/docs/specs/man/jar.html

general-purpose archiving/compression tool based on ZIP/ZLIB

preferred packaging/deployment mechanism since Java 1.1

heavily influenced by TAR (Tape ARchive); hence JAR (Java ARchive)

CLI tool uses Unix-style CLI parameters

built using primarily java.base:java.util.jar APIs

https://docs.oracle.com/en/java/javase/17/docs/specs/jar/jar.html

jar

Main Operation Modes

-c | --create: Creates the archive

-t | --list: Lists the contents for the archive

-u | --update: Updates an existing JAR file

-x | --extract: Extracts contents of a JAR file

Modifiers

-v | --verbose: Print verbose output to stdout

-f=FILE | --file=FILE: specifies the archive filename FILE

-C DIR: changes to the specified directory and includes the files specified

@FILE: CLI options can be found in FILE

jar

Examples

jar --create --file classes.jar Foo.class Bar.class

Creates classes.jar containing Foo.class and Bar.class

jar -cf classes.jar Foo.class Bar.class

Synonym to the above

jar tvf classes.jar

Verbosely list all contents of classes.jar

jar

JAR preserves directory paths

this is necessary for packages to operate correctly

com.newardassociates.Foo must be classfile Foo.class in com/newardassociates inside JAR

package root must start from JAR filesystem root

META-INF directory is "special" for metadata and related resources

META-INF/MANIFEST.MF is a "manifest" file describing the JAR file

jar

Manifest file

a collection of "Name: Value" pairs, one per line

https://docs.oracle.com/en/java/javase/17/docs/specs/jar/jar.html#jar-manifest

Names are specific to trigger important functionality

include a manifest file in the creation/update via -m=FILE or --mainfest=FILE

specifically do not create a manifest via -M or --no-manifest

jar

Common attributes

Manifest-Version: the version of the manifest file

Class-Path: relative URLs of dependent libraries

Main-Class: the classname whose main to invoke when run with java -jar FILE.jar

can also specify via -e=CLASSNAME or --main-class=CLASSNAME

Launcher-Agent-Class: classname of the java agent to launch before execution

unrecognized attributes are ignored by the JVM

jar

Multi-release JARs

JAR files can support multiple major versions of Java platform releases

set Multi-Release manifest to true

each versioned resource is in its own JAR directory: META-INF/versions/N

public API must be exactly identical across versions

jar

JARs and Services

the "Service Loader" functionality of the JVM

jar

JARs and Modules

a JAR is a "modular JAR" when it has 1+ module descriptor(s) within it

aka module-info.class in a non-META-INF directory path

this allows for the following CLI parameters:

--module-version: Defines the

--hash-modules

--module-path

jcmd

Overview

send diagnostic commands to local JVM process

issues a diagnostic command

including a complete list of available commands

jcmd

Synopsis

$ jcmd -l

$ jcmd pid|main-class PerfCounter.print

$ jcmd pid|main-class -f filename

$ jcmd pid|main-class command [arguments]

jcmd

Some useful commands

PerfCounter.print

prints all the performance counters available

help

prints all the commands available on target

JFR.stop | JFR.start | JFR.dump

Java Flight Recorder start/stop/dump

Thread.print

dump thread stack trace

VM.flags | VM.command_line | VM.system_properties

list VM flags/command-line/system properties

GC.heap_dump filename=filename

create heap dump file

GC.class_histogram filename=filename

create object histogram

jstack

Overview

generates thread/stack trace

local process

core file

remote debug server

on Windows, requires additional components

dbgeng.dll (Debugging Tools for Windows)

PATH needs to include Hotspot DLL (client.dll | server.dll)

officially experimental and unsupported

jstack

Options

jstack options pid

-l

long listing, including information about java.util.concurrent locks

visualvm

VisualVM

https://visualvm.github.io

GUI monitoring tool for JVM processes

includes lightweight profiling capabilities

successor to JConsole

open-source

supports plugins

well-documented

visualvm

Starting VisualVM

Install

brew install visualvm (or some other package manager)

or download VisualVM and run it

use Applications window to select Java process

even VisualVM itself!

visualvm

VisualVM tabs

Overview

general view of the JVM settings

Monitor

tracking CPU, Heap, Classes, Threads

can also "Perform GC" and "Heap Dump"

Threads

tracking all threads (live, daemon, finished, etc)

can also "Thread Dump" (stack trace)

Sampler (collecting performance/memory data)

sample CPU

sample Memory

visualvm

Plugins

select Tools | Plugins

extensions to VisualVM functionality

OQL queries for heap-object queries, BTrace, etc

downloadable directly from VisualVM

open API

see VisualVM website docs

Summary

What have we done?

Explored a bunch of tools

Maybe learned a few new tricks?