Running Java by Hand - StefanSchade/Java-Core-JVM-Basics GitHub Wiki
Normally the IDE masks a lot of what’s going on, so here is an "hello world" kind of run through the compile process of a java program.
Input: Source files in a variety of languages
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Java (.java)
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Groovy (.groovy)
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Scala (.scala)
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Kotlin (.kt)
Processing: javac Compile source to bytecode
Output: Platform independend bytecode
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Class files (.class)
These classfiles can run on the Java Runtime environment or be packaged into libraries
Input: many .class files that make up one application (many might mean: thousands)
Processing: Combine files into a single file using ZIP Compression
Output: *.jar, *.war, *.ear
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Overview over Java archive types
File Ext: |
Name: |
contains: |
*.jar |
Java Archive |
ZIP file containig class files, typically not a complete application |
*.war |
Web Application Archive |
can include other jar files, webresources, and more, complete web application |
*.ear |
Enterprise Archive |
contains one or more war files meant to be deployed to an application server (Tomcat, Webboss, Websphere) |
FAT JAR |
aka. Uber JAR |
executable jar that contains all dependencies including embeded application server, used by Spring |
Docker Container |
Image contains Runtime Environment, JVM, Java Package (Fat Jar) deployment entity |
Input: Bytecode as class file, of forms
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Classfiles (.class)
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Jar (.jar)
Processing: java
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necessary class files and JARs must be in classpath (either specified as environment variable or comandline argument)
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main class must be called explicitly
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generate source file "HelloWorld.java" with a main routine
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compile:
javac HelloWorld.java -
run:
java Helloworld
Now create a JAR containing HelloWorld
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create jar: jar cf helloworld.jar HelloWorld.class
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run jar: java -classpath helloworld.jar HelloWorld