Java SE is a very impressive platform indeed, but with all that functionality comes a large and ever increasing footprint.  It stands to reason then that one of the more frequent requests from the community has been the desire to deploy only those components required for a particular application instead of the entire Java SE runtime environment.  Referred to as subsetting, the benefits of such a concept would seem to be many:

• A smaller Java environment would require less compute resources, thus opening up a new domain of devices previously thought to be too humble for Java.
• A smaller runtime environment could be better optimized for performance and start up time.
• Elimination of unused code is always a good idea from a security perspective.
• If the environment could be pared down significantly, there may be tremendous benefit to bundling runtimes with each individual Java application.
• These bundled applications could be downloaded more quickly.

Despite these perceived advantages, the platform stewards (Sun, then Oracle) have been steadfast in their resistance to subsetting.  The rationale for such a stance is quite simple: there was sincere concern that the Java SE platform would fragment.  Agree or disagree, the Java SE standard has remained remarkably in tact over time.  If you need any further evidence of this assertion, compare the state of Java SE to that of Java ME, particularly in the mobile telephony arena.  Better still, look how quickly Android has spawned countless variants in its brief lifespan.

Nonetheless, a formal effort has been underway having the stated goal of providing a much more modular Java platform.  Called Project Jigsaw, when complete, Java SE will be composed of a set of finer-grained modules and will include tools to enable developers to identify and isolate only those modules needed for their application.  However, implementing this massive internal change and yet maintaining compatibility has proven to be a considerable challenge.  Consequently full implementation of the modular Java platform has been delayed until Java 9.

Understanding that Java 9 is quite a ways off, an interim solution will be available for Java 8, called Compact Profiles.  Rather than specifying a complete module system, Java 8 will define subset profiles of the Java SE platform specification that developers can use to deploy.  At the current time three compact profiles have been defined, and have been assigned the creative names compact1, compact2, and compact3. The table that follows lists the packages that comprise each of the profiles.  Each successive profile is a superset of its predecessor.  That is to say, the compact2 profile contains all of the packages in compact1 plus those listed under the compact2 column below.  Likewise, compact3 contains all of compact2 packages plus the ones listed in the compact3 column.

compact1                     compact2                    compact3
--------------------------   -----------------------     --------------------------
java.io                      java.rmi                    java.lang.instrument
java.lang                    java.rmi.activation         java.lang.management
java.lang.annotation         java.rmi.registry           java.security.acl
java.lang.invoke             java.rmi.server             java.util.prefs
java.lang.ref                java.sql                    javax.annotation.processing
java.lang.reflect            javax.rmi.ssl               javax.lang.model
java.math                    javax.sql                   javax.lang.model.element
java.net                     javax.transaction           javax.lang.model.type
java.nio                     javax.transaction.xa        javax.lang.model.util
java.nio.channels            javax.xml                   javax.management
java.nio.channels.spi        javax.xml.datatype          javax.management.loading
java.nio.charset             javax.xml.namespace         javax.management.modelbean
java.nio.charset.spi         javax.xml.parsers           javax.management.monitor
java.nio.file                javax.xml.stream            javax.management.openmbean
java.nio.file.attribute      javax.xml.stream.events     javax.management.relation
java.nio.file.spi            javax.xml.stream.util       javax.management.remote
java.security                javax.xml.transform         javax.management.remote.rmi
java.security.cert           javax.xml.transform.dom     javax.management.timer
java.security.interfaces     javax.xml.transform.sax     javax.naming
java.security.spec           javax.xml.transform.stax    javax.naming.directory
java.text                    javax.xml.transform.stream  javax.naming.event
java.text.spi                javax.xml.validation        javax.naming.ldap
java.util                    javax.xml.xpath             javax.naming.spi
java.util.concurrent         org.w3c.dom                 javax.script
java.util.concurrent.atomic  org.w3c.dom.bootstrap       javax.security.auth.kerberos
java.util.concurrent.locks   org.w3c.dom.events          javax.security.sasl
java.util.jar                org.w3c.dom.ls              javax.sql.rowset
java.util.logging            org.xml.sax                 javax.sql.rowset.serial
java.util.regex              org.xml.sax.ext             javax.sql.rowset.spi
java.util.spi                org.xml.sax.helpers         javax.tools
java.util.zip                                            javax.xml.crypto
javax.crypto                                             javax.xml.crypto.dom
javax.crypto.interfaces                                  javax.xml.crypto.dsig
javax.crypto.spec                                        javax.xml.crypto.dsig.dom
javax.net                                                javax.xml.crypto.dsig.keyinfo
javax.net.ssl                                            javax.xml.crypto.dsig.spec
javax.security.auth                                      org.ieft.jgss
javax.security.auth.callback
javax.security.auth.login
javax.security.auth.spi
javax.security.auth.x500
javax.security.cert

You may ask what savings can be realized by using compact profiles?  As Java 8 is in pre-release stage, numbers will change over time, but let's take a look at a snapshot early access build of Java SE-Embedded 8 for ARMv5/Linux. A reasonably configured compact1 profile comes in at less than 14MB.  Compact2 is about 18MB and compact3 is in the neighborhood of 21MB.  For reference, the latest Java 7u21 SE Embedded ARMv5/Linux environment requires 45MB.

So at less than one-third the original size of the already space-optimized Java SE-Embedded release, you have a very capable runtime environment.  If you need the additional functionality provided by the compact2 and compact3 profiles or even the full VM, you have the option of deploying your application with them instead.

In the next installment, we'll look at Compact Profiles in a bit more detail.