Java

NOT PORTED YET.

Books
SDKman - Install and Manage Multiple Versions of Java at the same time
Show Java Classpath
Inspect JAR contents
JKS - Java Key Store (SSL)
Java Decompilers
Libraries
- JitPack.io
JShell
JBang
- JBang CLI
GraalJS
Clojure
ProGuard
JVM Distributions
- Corretto
- Gluon
- GraalVM
- Java.net
- JetBrains
- Liberica
- Mandrel
- Microsoft
- Oracle
- SapMachine
- Semeru
- Temurin
- Tencent
- Zulu
Memes

Books

SDKman - Install and Manage Multiple Versions of Java at the same time

See SDKman page.

Show Java Classpath

Since the java -cp / java -classpath is one huge string of colon separated paths, it's nicer to show them one per line using the scripts in DevOps-Bash-tools or DevOps-Perl-tools repos:

java_show_classpath.sh

java_show_classpath.pl

Crude shell pipeline to do similar:

ps -ef |
grep java |
tee /dev/stderr |
awk '{print $2}' |
xargs -L1 jinfo |
grep java.class.path  |
tr ':' '\n'

although if it's just jinfo you're missing in the $PATH it would be better to just:

PATH="$PATH:/path/to/bin/containing/jinfo" java_show_classpath.sh

Inspect JAR contents

Java jar files are just tars of the byte-compiled Java classes.

You can inspect them using the good old unix tar command, eg.:

jar tf mysql-connector-j-*.jar

tar tvf mysql-connector-j-*.jar

The directory layout of the class files corresponds to the class hierarchy eg. is accessed as com.mysql.jdbc.Driver in Java code.

JKS - Java Key Store (SSL)

See SSL doc.

Java Decompilers

Use these to decompile JAR or .class files to read the Java source code.

Using DevOps-Bash-tools repo:

For a GUI:

jd_gui.sh "$jar_or_class_file"

bytecode_viewer.sh

For command line output:

cfr.sh "$jar_or_class_file"

procyon.sh "$jar_or_class_file"

Libraries

Some libraries of interest:

Faker - generates fake but realistic data for unit testing

JitPack.io

https://jitpack.io/

https://docs.jitpack.io/

Package repo for JVM and Android projects.

Builds Git projects on demand and provides ready-to-use artifacts (jar, aar).

To check if a Jitpack dependency target is valid:

GITHUB_REPO="markomilos/paginate"
VERSION="v1.0.0"

curl -IsSLf "https://jitpack.io/com/github/$GITHUB_REPO/$VERSION/${GITHUB_REPO##*/}-$VERSION.jar"

For an Android dependency, check for the .aar artifact instead of .jar

curl -IsSLf "https://jitpack.io/com/github/$GITHUB_REPO/$VERSION/${GITHUB_REPO##*/}-$VERSION.aar"

Check build log to show what was built by JitPack:

curl "https://jitpack.io/com/github/$GITHUB_REPO/$VERSION/" && echo

JShell

Command line or interactive Java Shell.

Java 9+:

$ jshell
|  Welcome to JShell -- Version 21.0.4
|  For an introduction type: /help intro

jshell>

See also Groovy which is one of my favourite languages and has a shell:

groovysh

JBang

https://www.jbang.dev/

https://github.com/jbangdev

Packages executable self-contained source-only Java programs.

Install using SDKman:

sdk install jbang

Create a source code CLI program:

jbang init -t cli hellocli.java

Reading the source code it shebangs jbang and annotates the class with some metadata for jbang.

The first run downloads the dependencies mentioned in the source code

$ ./hellocli.java --help
[jbang] Resolving dependencies...
[jbang]    info.picocli:picocli:4.6.3
[jbang] Dependencies resolved
[jbang] Building jar for hellocli.java...
Usage: hellocli [-hV] <greeting>
hellocli made with jbang
      <greeting>   The greeting to print
  -h, --help       Show this help message and exit.
  -V, --version    Print version information and exit.

$ ./hellocli.java JBANG!
Hello JBANG!

Automatic fetches any dependencies referenced in the source code using //DEPS group:artifact:version comments or @Grab annotations.

Even downloads a JDK if needed.

This makes portable Java scripting easier.

JBang CLI

jbang -c 'Java_code'

Example of JBang CLI using Faker library to output random names:

// DEPS com.github.javafaker.javafaker:1.0.2

import com.github.javafaker.Faker

Faker faker = new Faker()

cat > /tmp/faker.java <<EOF
//usr/bin/env jbang "$0" "$@" ; exit $?
//DEPS com.github.javafaker:javafaker:1.0.2

import com.github.javafaker.Faker;
import java.util.stream.Stream;

public class faker {
    public static void main(String[] args) {
      Faker faker = new Faker();
      Stream.generate(faker.name()::fullName)
          .filter(s -> s.contains("Hari"))
          .forEach(s -> System.out.println(s + " is Awesome"));
    }
}
EOF

jbang /tmp/faker.java

See also Groovy which is one of my favourite languages and wish I had more excuses to code it in other than:

GraalJS

oracle/graaljs

JavaScript engine running on JVM via GraalVM.

ECMAScript-compliant runtime to execute JavaScript and Node.js applications on JVM with benefits of GraalVM stack including interoperability with Java.