Welcome!

Microservices Expo Authors: Elizabeth White, Pat Romanski, Dalibor Siroky, John Worthington, John Katrick

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 %@include...% 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
"Codigm is based on the cloud and we are here to explore marketing opportunities in America. Our mission is to make an ecosystem of the SW environment that anyone can understand, learn, teach, and develop the SW on the cloud," explained Sung Tae Ryu, CEO of Codigm, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"We're developing a software that is based on the cloud environment and we are providing those services to corporations and the general public," explained Seungmin Kim, CEO/CTO of SM Systems Inc., in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
The nature of test environments is inherently temporary—you set up an environment, run through an automated test suite, and then tear down the environment. If you can reduce the cycle time for this process down to hours or minutes, then you may be able to cut your test environment budgets considerably. The impact of cloud adoption on test environments is a valuable advancement in both cost savings and agility. The on-demand model takes advantage of public cloud APIs requiring only payment for t...
identify the sources of event storms and performance anomalies will require automated, real-time root-cause analysis. I think Enterprise Management Associates said it well: “The data and metrics collected at instrumentation points across the application ecosystem are essential to performance monitoring and root cause analysis. However, analytics capable of transforming data and metrics into an application-focused report or dashboards are what separates actual application monitoring from relat...
Many enterprise and government IT organizations are realizing the benefits of cloud computing by extending IT delivery and management processes across private and public cloud services. But they are often challenged with balancing the need for centralized cloud governance without stifling user-driven innovation. This strategy requires an approach that fundamentally reshapes how IT is delivered today, shifting the focus from infrastructure to services aggregation, and mixing and matching the bes...
"CA has been doing a lot of things in the area of DevOps. Now we have a complete set of tool sets in order to enable customers to go all the way from planning to development to testing down to release into the operations," explained Aruna Ravichandran, Vice President of Global Marketing and Strategy at CA Technologies, in this SYS-CON.tv interview at DevOps Summit at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"This all sounds great. But it's just not realistic." This is what a group of five senior IT executives told me during a workshop I held not long ago. We were working through an exercise on the organizational characteristics necessary to successfully execute a digital transformation, and the group was doing their ‘readout.' The executives loved everything we discussed and agreed that if such an environment existed, it would make transformation much easier. They just didn't believe it was reali...
DevOps teams have more on their plate than ever. As infrastructure needs grow, so does the time required to ensure that everything's running smoothly. This makes automation crucial - especially in the server and network monitoring world. Server monitoring tools can save teams time by automating server management and providing real-time performance updates. As budgets reset for the New Year, there is no better time to implement a new server monitoring tool (or re-evaluate your current solution)....
While some developers care passionately about how data centers and clouds are architected, for most, it is only the end result that matters. To the majority of companies, technology exists to solve a business problem, and only delivers value when it is solving that problem. 2017 brings the mainstream adoption of containers for production workloads. In his session at 21st Cloud Expo, Ben McCormack, VP of Operations at Evernote, discussed how data centers of the future will be managed, how the p...
While we understand Agile as a means to accelerate innovation, manage uncertainty and cope with ambiguity, many are inclined to think that it conflicts with the objectives of traditional engineering projects, such as building a highway, skyscraper or power plant. These are plan-driven and predictive projects that seek to avoid any uncertainty. This type of thinking, however, is short-sighted. Agile approaches are valuable in controlling uncertainty because they constrain the complexity that ste...
High-velocity engineering teams are applying not only continuous delivery processes, but also lessons in experimentation from established leaders like Amazon, Netflix, and Facebook. These companies have made experimentation a foundation for their release processes, allowing them to try out major feature releases and redesigns within smaller groups before making them broadly available. In his session at 21st Cloud Expo, Brian Lucas, Senior Staff Engineer at Optimizely, discussed how by using ne...
The benefits of automation are well documented; it increases productivity, cuts cost and minimizes errors. It eliminates repetitive manual tasks, freeing us up to be more innovative. By that logic, surely, we should automate everything possible, right? So, is attempting to automate everything a sensible - even feasible - goal? In a word: no. Consider this your short guide as to what to automate and what not to automate.
Agile has finally jumped the technology shark, expanding outside the software world. Enterprises are now increasingly adopting Agile practices across their organizations in order to successfully navigate the disruptive waters that threaten to drown them. In our quest for establishing change as a core competency in our organizations, this business-centric notion of Agile is an essential component of Agile Digital Transformation. In the years since the publication of the Agile Manifesto, the conn...
We just came off of a review of a product that handles both containers and virtual machines in the same interface. Under the covers, implementation of containers defaults to LXC, though recently Docker support was added. When reading online, or searching for information, increasingly we see “Container Management” products listed as competitors to Docker, when in reality things like Rocket, LXC/LXD, and Virtualization are Dockers competitors. After doing some looking around, we have decided tha...
The cloud revolution in enterprises has very clearly crossed the phase of proof-of-concepts into a truly mainstream adoption. One of most popular enterprise-wide initiatives currently going on are “cloud migration” programs of some kind or another. Finding business value for these programs is not hard to fathom – they include hyperelasticity in infrastructure consumption, subscription based models, and agility derived from rapid speed of deployment of applications. These factors will continue to...
"We are an integrator of carrier ethernet and bandwidth to get people to connect to the cloud, to the SaaS providers, and the IaaS providers all on ethernet," explained Paul Mako, CEO & CTO of Massive Networks, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
From our perspective as consumers, perhaps the best thing about digital transformation is how consumerization is making technology so much easier to use. Sure, our television remote controls still have too many buttons, and I have yet to figure out the digital display in my Honda, but all in all, tech is getting easier for everybody. Within companies – even very large ones – the consumerization of technology is gradually taking hold as well. There are now simple mobile apps for a wide range of ...
"I focus on what we are calling CAST Highlight, which is our SaaS application portfolio analysis tool. It is an extremely lightweight tool that can integrate with pretty much any build process right now," explained Andrew Siegmund, Application Migration Specialist for CAST, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
We all know that end users experience the Internet primarily with mobile devices. From an app development perspective, we know that successfully responding to the needs of mobile customers depends on rapid DevOps – failing fast, in short, until the right solution evolves in your customers' relationship to your business. Whether you’re decomposing an SOA monolith, or developing a new application cloud natively, it’s not a question of using microservices – not doing so will be a path to eventual b...
"Cloud4U builds software services that help people build DevOps platforms for cloud-based software and using our platform people can draw a picture of the system, network, software," explained Kihyeon Kim, CEO and Head of R&D at Cloud4U, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.