Front cover IBM Technology for Java Virtual Machine in IBM i5/OS Most information about 32-bit JVM applies to all IBM server platforms Comprehensive book on new 32-bit JVM in i5/OS Run WebSphere Application Server in 32-bit JVM Aleksandr Nartovich Adam Smye-Rumsby Paul Stimets George Weaver ibm.com/redbooks International Technical Support Organization IBM Technology for Java Virtual Machine in IBM i5/OS February 2007 SG24-7353-00 Note: Before using this information and the product it supports, read the information in “Notices” on page vii. First Edition (February 2007) This edition applies to IBM® Developer Kit and Runtime Environment, Java™ 2 Technology Edition, Version 5.0. © Copyright International Business Machines Corporation 2007. All rights reserved. Note to U.S. Government Users Restricted Rights -- Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp. Contents Notices . vii Trademarks . viii Preface . ix The team that wrote this IBM Redbook . ix Become a published author . .x Comments welcome. .x Chapter 1. The world of Java . 1 1.1 Java: language and platform. 2 1.1.1 Java language. 2 1.1.2 Java platform and Java software development kit . 3 1.2 Java Virtual Machine. 4 1.2.1 JVM architecture . 5 1.3 Java Runtime Environment . 7 1.4 Java platform development tools and API. 8 Chapter 2. Exploring IBM Technology for Java Virtual Machine . 9 2.1 A history of Classic JVM and IBM Technology for JVM on System i platform . 10 2.1.1 The System i Classic JVM . 10 2.1.2 IBM Technology for Java Virtual Machine. 12 2.2 Comparing IBM Technology for JVM and Classic JVM. 13 2.2.1 Similarities. 13 2.2.2 Differences . 13 2.3 Choosing IBM Technology for JVM or Classic JVM . 15 2.4 Using IBM Technology for JVM with existing applications . 16 2.5 Future JVM developments on i5/OS . 16 Chapter 3. New user guide . 19 3.1 i5/OS portable application solutions environment . 20 3.2 Installing IBM Technology for JVM . 20 3.2.1 Checking prerequisites . 20 3.2.2 Installing IBM Technology for JVM . 21 3.2.3 Verifying the installation . 22 3.2.4 Uninstalling IBM Technology for JVM . 22 3.3 Basic configuration . 23 3.3.1 Setting JAVA_HOME . 23 3.3.2 Setting default command line options in SystemDefault.properties file . 25 3.4 Known issues . 25 Chapter 4. Making the switch to IBM Technology for JVM . 27 4.1 Fitting your application into a 32-bit JVM . 28 4.1.1 Measuring heap usage in Classic JVM. 29 4.2 Configuring garbage collection . 30 4.2.1 Choosing the right policy. 30 4.2.2 The minimum and maximum heap size . 31 4.3 Finding dependencies to the Classic JVM . 32 4.4 WebSphere Application Server and IBM Technology for JVM . 33 © Copyright IBM Corp. 2007. All rights reserved. iii Chapter 5. Tuning the garbage collector. 35 5.1 Introduction to garbage collection . 36 5.1.1 Garbage collection in IBM Technology for JVM . 36 5.2 Available options . 37 5.2.1 Garbage collection policies . 37 5.2.2 Tuning heap size. 41 5.2.3 Verbose GC output . 44 5.3 Choosing the right policy. 46 Chapter 6. Optimizing performance with shared classes . 49 6.1 Introduction to shared classes . 50 6.1.1 Classes and classloaders . 50 6.1.2 Overview of shared classes . 52 6.1.3 History of shared classes . 52 6.1.4 Shared classes and user-defined classloaders. 53 6.2 Shared classes in IBM Technology for JVM . 53 6.2.1 The class cache . 53 6.2.2 Deploying shared classes . 54 6.2.3 Recommendations for shared classes . 60 6.3 Shared classes and application performance . 62 6.3.1 When to use shared classes. 62 6.3.2 Overheads associated with shared classes . 62 6.3.3 Performance gains with shared classes . 63 6.4 Shared Classes Helper API . 63 6.4.1 Helper API overview . 63 6.4.2 Helper API usage . 64 6.4.3 Shared Classes Helper API example . 65 6.4.4 Shared Classes Helper API Javadoc . 66 6.5 Security considerations . 67 6.5.1 Operating system security. 67 6.5.2 Java security . 67 6.6 Bytecode modification . 68 Chapter 7. Java Native Interface . ..