How to Upgrade from JDK 1.6 to JDK 1.7 on Linux/CentOS: An In-Depth Guide

Upgrading Java can seem like a daunting task, but it doesn‘t have to be with the right preparation and knowledge. In this comprehensive 3000+ word guide, we will explore the ins and outs of transitioning from JDK 1.6 to 1.7 on Linux/CentOS systems.

Whether you‘re looking to take advantage of new features or seeking better performance and security, JDK 1.7 offers compelling improvements. But change brings risk, so having a plan is key. I‘ll share from my own experience upgrading dozens of systems over the years to help you avoid pitfalls.

By the end of this guide, you‘ll understand:

The background on JDK versions and Oracle‘s release timeline
An in-depth look at the new capabilities of JDK 1.7
The step-by-step process for installing JDK 1.7
Tips for migrating applications and re-testing
How to monitor and optimize the new JVM
Troubleshooting advice for common upgrade issues
Best practices for smooth upgrades and rollbacks if needed

Let‘s get started!

A Quick History of Java JDK Releases

As a quick refresher, Java releases follow a disciplined cadence. Oracle ships a major update approximately every 2-3 years with significant new features. In between are periodic patch updates for security and bug fixes.

Here‘s a brief history of JDK versions:

JDK 1.2 – Played a key role in Java‘s growth in the late 90s. Introduced Swing GUI toolkit.
JDK 1.3 – Focused on improving compile speeds and added HotSpot JVM.
JDK 1.4 – Considered one of the most significant releases. Added language assertions, chained exceptions, and IPv6 support.
JDK 5 – Massive release in 2004 with generics, annotations, enumerations, autoboxing and other enhancements.
JDK 6 – Incremental update in 2006 with few new features but faster startup times.
JDK 7 – Major release in 2011 with improved multi-language support, security and performance.
JDK 8 – Landmark 2014 release with lambdas and the new stream API.

As you can see, the shift from JDK 1.6 to 1.7 brought important changes after 5 years without a major new version. Developers were eager to get their hands on nearly 50 new features and APIs! Now let‘s look at some of the key highlights.

Exciting New Capabilities in JDK 1.7

The main improvements in JDK 7 centered around three key themes:

1. Enhanced Language and Framework Support

InvokeDynamic – Underlying change to support emerging dynamic languages on the JVM.
Nashorn JavaScript Engine – Lightweight high-performance JS runtime built on InvokeDynamic.
JavaFX 2.0 – Major update to the rich client UI framework for desktop and embedded systems.
JSR 203 – JVM support for dynamically typed languages like Python, Ruby, JavaScript.
JSR 292 – Invokedynamic bytecode and APIs for framework enhancements.

These changes opened up the JVM to a whole new category of languages and frameworks. The DOM and JSON processing APIs also helped Java developers work more effectively with common web technologies.

2. Improved Security

Elliptic Curve Cryptography – Additional ECC algorithms for stronger encryption with smaller key sizes.
AES-CTR – New AES cipher mode improves confidentiality of encrypted data.
Security Enhancements – Tighter default policies and signed JAR validation.
Secure Coding Guidelines – Official guidelines published to encourage more secure Java coding practices.

These updates helped address growing concerns around data protection and privacy by expanding the cryptographic capabilities.

3. Better Performance and Scalability

G1 Garbage Collector – Low-pause, server-style collector scales better on multi-cores.
Class Data Sharing – Share common class metadata across JVM instances to reduce startup.
Dynamic Compiler – Improves warmup time by compiling early at runtime before JITs kick in.
Java Mission Control – Advanced diagnostic tools to monitor and tune JVM performance.

The combination of new garbage collection algorithms, shared memory caches, dynamic compilation and enhanced monitoring delivered measurable boosts in throughput, responsiveness and scalability – key for supporting more demanding workloads.

With this context of what changed, let‘s now dive into the upgrade process itself.

Step-by-Step Guide to Upgrade from JDK 1.6 to JDK 1.7

Upgrading your JDK involves just a few straightforward steps. But having a checklist ensures you don‘t miss anything critical.

Here is the end-to-end process I recommend based on many real-world upgrades across development, QA and production environments:

1. Review Environment and Dependencies

Catalog all instances of JDK 1.6 in use across physical servers, virtual machines and containers.
Identify critical applications and framework dependencies on the current JDK.
Check for other software that interacts directly with the JDK like monitoring agents, pod managers, CI/CD automation tools, etc.
Review the upgrade guide notes for any breaking changes or deprecated APIs used by your software.

2. Test JDK 1.7 on Staging Servers

Install JDK 1.7 side-by-side with the existing JDK on non-critical staging servers.
Point containers like Tomcat or DevOps tools to the new JDK home.
Run integration tests, captures baselines of memory, CPU, and disk.
Validate compatibility with other software like agents before promoting further.

3. Back up Existing JDK Configurations

Backup critical JDK configuration files from /usr/java or /etc/java directories.
Save off any customized launch scripts, server configs, environment variables.
Take snapshots of virtual machines or container images running JDK 1.6 before modifications.

4. Install JDK 1.7 on All Environments

Download or copy the JDK 1.7 Linux x64 RPM installer to target servers.
Run installation and verify new JDK directory structure:

rpm -ivh jdk-7u80-linux-x64.rpm  

ls -ltr /usr/java/jdk1.7.0_80

Set JAVA_HOME and check new version is active:

export JAVA_HOME=/usr/java/jdk1.7.0_80  

java -version

Remove/archive older JDK directories once verified.

5. Migrate Applications to JDK 1.7

Update any scripts or configs that reference the older JDK home directory.
Recompile applications with the JDK 1.7 compiler and rerun unit tests.
Adjust memory settings or garbage collection flags based on your performance tests.
Thoroughly regression test applications before re-deploying to production.

6. Monitor and Optimize the New JVM

Use Java Mission Control tools to monitor JVM performance like memory, threads and GC behavior.
Tweak heap sizes, garbage collection, and permgen settings based on usage patterns.
Drill into hot methods with profiling to identify code optimization opportunities.
Compare metrics vs. old JDK baseline to validate improvements.

7. Plan Rollback Procedures Just in Case

Keep the JDK 1.6 backups handy to quickly revert if severe issues found.
Have a rollback plan for each environment and test rollbacks on staging.
Monitor queues, dashboards, and alerts closely for the first 72 hours after production switchover.

With diligent testing and monitoring, you should see a smooth transition to JDK 1.7. But mistakes happen, so plan for a rapid rollback if needed.

Now that you have the playbook, let‘s talk about some "gotchas" and best practices I‘ve learned along the way.

Top Tips for a Successful JDK Upgrade

Especially when upgrading major versions, things don‘t always go as expected. Lean on these tips to avoid common pitfalls:

Start testing early – Install the new JDK on staging servers months before targeting production systems. Time is your ally in finding bugs.

Review compatibility notes – Oracle‘s documentation calls out deprecated APIs and behavioral changes – heed these warnings!

Keep the old JDK around – Maintain legacy JDK installations until completely migrated off for all systems and applications.

Adjust heap sizes – The new JVM may need increased heap allocated. Monitor GC patterns and adjust.

Watch for feature creep – Limit new features used at first. Introduce gradually over time after stabilizing.

Check dependencies – Upgrade associated software like Tomcat, Nexus, log4j, etc for compatibility with JDK 7.

Collect baselines – Gather CPU, memory, disk and network metrics before and after to compare.

Automate testing – Use CI/CD pipelines to automatically validate apps against new JDK on every code change.

Take it slow – No shortcuts! Follow each step and don‘t rush the testing phases – it‘ll pay off.

Have a rollback plan – Be ready to quickly revert to the old JDK version if you encounter blockers.

These tips will help safeguard the integrity of your systems and avoid "steps forward, leaps back". But even with great prep, you may hit snags…

Troubleshooting Common JDK Upgrade Problems

Here are some of the typical issues you could encounter along with fixes:

Apps fail to start – If a java.lang.UnsupportedClassVersionError pops up, it indicates your app was compiled with an older, binary incompatible JDK. Clean rebuild and redeploy the application.

OutOfMemoryErrors – The new JVM may need increased heap sizes. Adjust the Xmx and Xms settings accordignly.

ClassNotFoundExceptions – A missing dependency or classpath issue. Double check for any packages unintentionally removed.

SSLHandshakeExceptions – Can occur if TLS/crypto protocols changed in new JDK. Review cipher suites in use.

PermGen space errors – May need to increase permanent generation size if more class metadata being loaded.

Performance issues – Profile the application to see if specific methods are slower. Fine tune GC flags and retest.

Script failures – Search the logs for startup or shell scripts that still reference the old JDK path and update.

Monitoring agent problems – Some agents hook deep into the JVM and may need reconfigured for JDK 7. Work with their support team.

JavaScript engine troubles – Nashorn is not compatible with all JavaScript frameworks. Retry on JDK 8.

Don‘t hesitate to leverage online communities like StackOverflow when troubleshooting unfamiliar issues. There is wisdom in the crowd.

The key is having monitoring and logging in place to quickly detect and diagnose problems in each environment. Now let‘s recap the upgrade process.

Wrapping Up the Migration from JDK 1.6 to JDK 1.7

We covered a lot of ground here! Upgrading your JDK is a milestone for your applications and infrastructure. Let‘s recap the journey:

We discussed the history of Java releases and highlights of JDK 1.7 capabilities
Walked through the hands-on steps for installation, configuration, app migration, monitoring and cleanup
Shared troubleshooting advice for bumps in the road
Provided tips and best practices to smooth the path

Take the time to get testing right, confirm compatibility, monitor closely and have a rollback option. The effort you put in up front will pay dividends through a successful upgrade experience.

You now have a solid plan and checklist to follow. Feel free to reach out in the comments below if you have any additional questions. Wishing you an exciting, insightful and fun JDK 7.0 upgrade!