Welcome!

Microservices Expo Authors: Pat Romanski, Liz McMillan, Elizabeth White, Gordon Haff, Carmen Gonzalez

Related Topics: Java IoT, Industrial IoT, Microservices Expo, IBM Cloud, Weblogic, Machine Learning

Java IoT: Article

Java Method Size

Getting around the 64K limit

The Java Virtual Machine specification limits the size of generated Java byte code for each method in a class to the maximum of 64K bytes. This limitation will cause the JVM to throw java.lang.VerifyError at runtime when the method size exceeds this limit.

This method size restriction of the JVM seems to be too stringent. A bug is open with the Oracle Java development team (http://bugs.sun.com/view_bug.do?bug_id=4262078). This bug is taken as an enhancement request which is likely to be fixed in the future java versions. That said, the fix for this issue is rather supportive. Application/Container developers need to consider few factors and apply good programming/refactoring techniques to get around this problem. While future versions of JVM might increase the method size limit to a considerable extent, a the size will always be a finite value.

In this article, I discuss some of the techniques that can be used to get around this problem. The techniques/suggestions discussed here, while apply to development environments also, are primarily targeted for containers which involve code generation as part of compilation process (e.g., EJB container or a JSP container).

Applications and Method Size Limit
While applications written in Java seldom encounter this issue, even more so after the above noted bug is fixed, it is recommended to follow the proven software engineering principles like code refactoring and object oriented programming techniques.

The complexity of this issue in application development is relatively smaller. As the code is written through the development phase, a number of tests are run both at the Unit level as well as the system level. Also, it is very rare that the application development involves complex code generation during the build time. This gives the developer/architect an opportunity to identify the possible method size restriction issue well ahead of the final delivery.

Application Containers and Method Size Limit
Application Containers are environments where Java applications execute. So they carry very high degree of complexity in terms of code. As the containers consume the application code and configuration and provide services for the application runtime, containers most often involve code generation. This code generation can be very complex in systems like JSP compiler as they convert scripting languages to Java.

This makes containers involving code generation particularly vulnerable to the Java method size limit restriction.

Techniques for Resolving the Method Size Restriction
In this section, I detail some of the techniques which can be used in code generation area to cover most of the use cases which cause the method size restriction.

Splitting a Big Method into Smaller Pieces
This is one of the structured programming techniques which can be used with effect. The driving factor for this technique should be the code refactoring. After the code generation is completed, a careful examination of the bigger methods can give us some clue of moving some of the java statements to a different private method. This is typically reverse engineering the output to a fine grained control.

Using a Intermediate Super Class
This applies particularly to areas such as EJB and JSP. A JSP file once converted into a Java class will typically extend a JspServlet class (implemented differently by different container vendors). The core refactoring technique here is to move the rudimentary code into the super class so that the generated class becomes light. However, this technique is fairly primitive. Most modern container vendors have already optimized their code to include almost everything possible into their super class implementation.

Using Helper Class/Methods
The third refactoring technique is to use a helper class. One particular use case is a JSP compiler handling a [email protected]..% directive. JSP specification mandates that the static includes need to be expanded inline in the generated service method. This adds to the size of the generated service method. One refactoring that can be used here is to move the expanded code into a private member function in the generated Java file and include just the method call in the service method.

Another area is the scripting elements in the JSP file. All the scripting elements are parsed and then included inline in the generated service() method of the java file. A similar refactoring technique discussed above can be used for the scripting elements as well.

Code generation engines can consider generating a Helper class which contains all the refactored methods and shield the Helper class from end-user's direct access.

Using JVM Switches
Java compilers generate .class files, with each file containing bytecodes for the methods in one class. These files contain a series of sections, or attributes, and it's possible to exercise some control over which sections actually show up in a .class file. The Code attribute contains actual bytecodes for methods, SourceFile information on the source file name used to generate this .class file, LineNumberTable mapping information between bytecode offsets and source file line numbers, and LocalVariableTable mapping information between stack frame offsets and local variable names.

We can use options to the javac compiler to control which sections are included:

javac Code, SourceFile, LineNumberTable
javac -g Code, SourceFile, LineNumberTable, LocalVariableTable
javac -g:none Code

How much do these options affect code size? A test using the JDK 1.2.2 sources in the java.io, java.lang, and java.util packages was run, with total sizes of all .class files as follows:

javac 668K
javac -g 815K
javac -g:none 550K

So use of javac -g:none saves about 20% in space over the default javac, and using javac -g is about 20% larger than the default. There are also commercial tools that tackle this particular problem.

If you strip out information such as line numbers from .class files, you may have problems with debugging and exception reporting. So it is recommended that the container vendors provide a configuration mechanism to switch off/on this feature so the production environments can take advantage.

Conclusion
Any refactoring technique will not completely alleviate the method size restriction. Excessive template text and scripting elements in the scripting languages will almost always cause the compilers to generate heavier methods and may lead to the method size restriction. The solution to this problem is supportive. Developers need to concentrate on good programming techniques so that the scripting language code like JSP will be more maintainable. JSP specification recommends using tag libraries that promote reusability while considerably reducing the size of the generated service method.

More Stories By Shankar Itchapurapu

Shankar Itchapurapu is a software engineer at Oracle in India. He holds a Master's degree in Computer Applications. You can e-mail Shankar at [email protected]

@MicroservicesExpo Stories
DevOps tends to focus on the relationship between Dev and Ops, putting an emphasis on the ops and application infrastructure. But that’s changing with microservices architectures. In her session at DevOps Summit, Lori MacVittie, Evangelist for F5 Networks, will focus on how microservices are changing the underlying architectures needed to scale, secure and deliver applications based on highly distributed (micro) services and why that means an expansion into “the network” for DevOps.
"Plutora provides release and testing environment capabilities to the enterprise," explained Dalibor Siroky, Director and Co-founder of Plutora, in this SYS-CON.tv interview at @DevOpsSummit, held June 9-11, 2015, at the Javits Center in New York City.
Adding public cloud resources to an existing application can be a daunting process. The tools that you currently use to manage the software and hardware outside the cloud aren’t always the best tools to efficiently grow into the cloud. All of the major configuration management tools have cloud orchestration plugins that can be leveraged, but there are also cloud-native tools that can dramatically improve the efficiency of managing your application lifecycle. In his session at 18th Cloud Expo, ...
In his session at @DevOpsSummit at 19th Cloud Expo, Robert Doyle, lead architect at eCube Systems, will examine the issues and need for an agile infrastructure and show the advantages of capturing developer knowledge in an exportable file for migration into production. He will introduce the use of NXTmonitor, a next-generation DevOps tool that captures application environments, dependencies and start/stop procedures in a portable configuration file with an easy-to-use GUI. In addition to captur...
Docker containers have brought great opportunities to shorten the deployment process through continuous integration and the delivery of applications and microservices. This applies equally to enterprise data centers as well as the cloud. In his session at 20th Cloud Expo, Jari Kolehmainen, founder and CTO of Kontena, will discuss solutions and benefits of a deeply integrated deployment pipeline using technologies such as container management platforms, Docker containers, and the drone.io Cl tool...
We call it DevOps but much of the time there’s a lot more discussion about the needs and concerns of developers than there is about other groups. There’s a focus on improved and less isolated developer workflows. There are many discussions around collaboration, continuous integration and delivery, issue tracking, source code control, code review, IDEs, and xPaaS – and all the tools that enable those things. Changes in developer practices may come up – such as developers taking ownership of code ...
"We provide DevOps solutions. We also partner with some key players in the DevOps space and we use the technology that we partner with to engineer custom solutions for different organizations," stated Himanshu Chhetri, CTO of Addteq, in this SYS-CON.tv interview at DevOps at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
All organizations that did not originate this moment have a pre-existing culture as well as legacy technology and processes that can be more or less amenable to DevOps implementation. That organizational culture is influenced by the personalities and management styles of Executive Management, the wider culture in which the organization is situated, and the personalities of key team members at all levels of the organization. This culture and entrenched interests usually throw a wrench in the work...
@DevOpsSummit at Cloud taking place June 6-8, 2017, at Javits Center, New York City, is co-located with the 20th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long developm...
"We're bringing out a new application monitoring system to the DevOps space. It manages large enterprise applications that are distributed throughout a node in many enterprises and we manage them as one collective," explained Kevin Barnes, President of eCube Systems, in this SYS-CON.tv interview at DevOps at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
I’m told that it has been 21 years since Scrum became public when Jeff Sutherland and I presented it at an Object-Oriented Programming, Systems, Languages & Applications (OOPSLA) workshop in Austin, TX, in October of 1995. Time sure does fly. Things mature. I’m still in the same building and at the same company where I first formulated Scrum.[1] Initially nobody knew of Scrum, yet it is now an open source body of knowledge translated into more than 30 languages[2] People use Scrum worldwide for ...
Thanks to Docker, it becomes very easy to leverage containers to build, ship, and run any Linux application on any kind of infrastructure. Docker is particularly helpful for microservice architectures because their successful implementation relies on a fast, efficient deployment mechanism – which is precisely one of the features of Docker. Microservice architectures are therefore becoming more popular, and are increasingly seen as an interesting option even for smaller projects, instead of being...
As the race for the presidency heats up, IT leaders would do well to recall the famous catchphrase from Bill Clinton’s successful 1992 campaign against George H. W. Bush: “It’s the economy, stupid.” That catchphrase is important, because IT economics are important. Especially when it comes to cloud. Application performance management (APM) for the cloud may turn out to be as much about those economics as it is about customer experience.
When you focus on a journey from up-close, you look at your own technical and cultural history and how you changed it for the benefit of the customer. This was our starting point: too many integration issues, 13 SWP days and very long cycles. It was evident that in this fast-paced industry we could no longer afford this reality. We needed something that would take us beyond reducing the development lifecycles, CI and Agile methodologies. We made a fundamental difference, even changed our culture...
The 20th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held June 6-8, 2017, at the Javits Center in New York City, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Containers, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal ...
@DevOpsSummit taking place June 6-8, 2017 at Javits Center, New York City, is co-located with the 20th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. @DevOpsSummit at Cloud Expo New York Call for Papers is now open.
SYS-CON Events announced today that Dataloop.IO, an innovator in cloud IT-monitoring whose products help organizations save time and money, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Dataloop.IO is an emerging software company on the cutting edge of major IT-infrastructure trends including cloud computing and microservices. The company, founded in the UK but now based in San Fran...
Synthetic monitoring is hardly a new technology. It’s been around almost as long as the commercial World Wide Web has. But the importance of monitoring the performance and availability of a web application by simulating users’ interactions with that application, from around the globe, has never been more important. We’ve seen prominent vendors in the broad APM space add this technology with new development or partnerships just in the last 18 months.
Updating DevOps to the latest production data slows down your development cycle. Probably it is due to slow, inefficient conventional storage and associated copy data management practices. In his session at @DevOpsSummit at 20th Cloud Expo, Dhiraj Sehgal, in Product and Solution at Tintri, will talk about DevOps and cloud-focused storage to update hundreds of child VMs (different flavors) with updates from a master VM in minutes, saving hours or even days in each development cycle. He will also...
SYS-CON Events announced today that Linux Academy, the foremost online Linux and cloud training platform and community, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Linux Academy was founded on the belief that providing high-quality, in-depth training should be available at an affordable price. Industry leaders in quality training, provided services, and student certification passes, its goal is to c...