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Classpath

Java has Bootstrap classes e.g. rt.jar found under jre/lib, Extension classes e.g. sunjce_provider.jar (cryptography) found under jre/lib/ext and Application classes.

Only application classes need to be specified in a classpath.


Setting the classpath

default (no classpath specified)	Searches in the current directory and subdirectories in the case of packages
set the $CLASSPATH variable	Overrides default
java -cp or -classpath	Overrides default and $CLASSPATH
java -jar	Overrides all other options. Class-Path: jar1.jar jar2.jar can be set in the manifest to refer to classes outside the main.jar

javac and javadoc can specify -sourcepath to limit the search for source files to only the specified sourcefile path.


jar - Java ARchive

• Allows for compression
• Can be signed
• Allows package sealing which specifies that all classes defined in the package must be in the same jar file

jar options

c	create
f	output to file named ...
v	verbose
m	include manifest information from file ... The supplied file must be UTF-8 and end with a newline/carriage return. (META-INF/MANIFEST.MF is created regardless)
0	turn off compression
C	allows a directory's contents to be jar'd into a different directory
t	lists (table of) contents
x	extract, this will overwrite any existing files
u	update, add or replace files or update the manifest
e	set entry point, overrides the manifest Main-Class

Contents of MANIFEST.MF

    Manifest-Version: 1.0
     // Automatically added

    Created-By: 1.7.0_06 (Oracle Corporation)
     // JDK version, automatically added

    Main-Class: classname

    Class-Path: directory/MyUtils.jar

    Name: name of specification
    Specification-Title: title
    Specification-Version: version
    Specification-Vendor: vendor

    Name: name of implementation
    Implementation-Title: title
    Implementation-Version: version
    Implementation-Vendor: vendor

    Name: directory/packageName
    Sealed: true
     // Can be repeated
     // If only Sealed: without preceding Name: then all packages are sealed


Jarsigner

Overwrites a jar with signed jar.

A signed jar contains a signature file XXX.SF. Each file, including the manifest has a SHA1-Digest: generated.

Signed jar files invoked by java -jar will be verified at runtime, or we can call jarsigner -verify myJar.jar.

jarsigner -keystore XXX
          -storepass XXX
          -keypass XXX
          myJar.jar
          alias

A keystore can hold several private keys, each of them aliased.




JNLP

Java Network Launch Protocol file