Click here to close now.


Java IoT Authors: Pat Romanski, Liz McMillan, Elizabeth White, AppDynamics Blog, Ed Featherston

Related Topics: Java IoT, Industrial IoT, Microservices Expo, IBM Cloud, Weblogic, IoT User Interface

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 ( 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.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.

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]

@ThingsExpo Stories
Through WebRTC, audio and video communications are being embedded more easily than ever into applications, helping carriers, enterprises and independent software vendors deliver greater functionality to their end users. With today’s business world increasingly focused on outcomes, users’ growing calls for ease of use, and businesses craving smarter, tighter integration, what’s the next step in delivering a richer, more immersive experience? That richer, more fully integrated experience comes about through a Communications Platform as a Service which allows for messaging, screen sharing, video...
The buzz continues for cloud, data analytics and the Internet of Things (IoT) and their collective impact across all industries. But a new conversation is emerging - how do companies use industry disruption and technology enablers to lead in markets undergoing change, uncertainty and ambiguity? Organizations of all sizes need to evolve and transform, often under massive pressure, as industry lines blur and merge and traditional business models are assaulted and turned upside down. In this new data-driven world, marketplaces reign supreme while interoperability, APIs and applications deliver un...
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data shows "less than 10 percent of IoT developers are making enough to support a reasonably sized team....
SYS-CON Events announced today that Dyn, the worldwide leader in Internet Performance, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Dyn is a cloud-based Internet Performance company. Dyn helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Through a world-class network and unrivaled, objective intelligence into Internet conditions, Dyn ensures traffic gets delivered faster, safer, and more reliably than ever.
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, will show how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants will get the download information, scripts, and complete end-to-end walkthrough of the analysis from start to finish. Participants will also be given the pract...
The IoT market is on track to hit $7.1 trillion in 2020. The reality is that only a handful of companies are ready for this massive demand. There are a lot of barriers, paint points, traps, and hidden roadblocks. How can we deal with these issues and challenges? The paradigm has changed. Old-style ad-hoc trial-and-error ways will certainly lead you to the dead end. What is mandatory is an overarching and adaptive approach to effectively handle the rapid changes and exponential growth.
Today’s connected world is moving from devices towards things, what this means is that by using increasingly low cost sensors embedded in devices we can create many new use cases. These span across use cases in cities, vehicles, home, offices, factories, retail environments, worksites, health, logistics, and health. These use cases rely on ubiquitous connectivity and generate massive amounts of data at scale. These technologies enable new business opportunities, ways to optimize and automate, along with new ways to engage with users.
Internet of Things (IoT) will be a hybrid ecosystem of diverse devices and sensors collaborating with operational and enterprise systems to create the next big application. In their session at @ThingsExpo, Bramh Gupta, founder and CEO of, and Fred Yatzeck, principal architect leading product development at, discussed how choosing the right middleware and integration strategy from the get-go will enable IoT solution developers to adapt and grow with the industry, while at the same time reduce Time to Market (TTM) by using plug and play capabilities offered by a robust IoT ...
Mobile messaging has been a popular communication channel for more than 20 years. Finnish engineer Matti Makkonen invented the idea for SMS (Short Message Service) in 1984, making his vision a reality on December 3, 1992 by sending the first message ("Happy Christmas") from a PC to a cell phone. Since then, the technology has evolved immensely, from both a technology standpoint, and in our everyday uses for it. Originally used for person-to-person (P2P) communication, i.e., Sally sends a text message to Betty – mobile messaging now offers tremendous value to businesses for customer and empl...
Can call centers hang up the phones for good? Intuitive Solutions did. WebRTC enabled this contact center provider to eliminate antiquated telephony and desktop phone infrastructure with a pure web-based solution, allowing them to expand beyond brick-and-mortar confines to a home-based agent model. It also ensured scalability and better service for customers, including MUY! Companies, one of the country's largest franchise restaurant companies with 232 Pizza Hut locations. This is one example of WebRTC adoption today, but the potential is limitless when powered by IoT.
You have your devices and your data, but what about the rest of your Internet of Things story? Two popular classes of technologies that nicely handle the Big Data analytics for Internet of Things are Apache Hadoop and NoSQL. Hadoop is designed for parallelizing analytical work across many servers and is ideal for the massive data volumes you create with IoT devices. NoSQL databases such as Apache HBase are ideal for storing and retrieving IoT data as “time series data.”
Clearly the way forward is to move to cloud be it bare metal, VMs or containers. One aspect of the current public clouds that is slowing this cloud migration is cloud lock-in. Every cloud vendor is trying to make it very difficult to move out once a customer has chosen their cloud. In his session at 17th Cloud Expo, Naveen Nimmu, CEO of Clouber, Inc., will advocate that making the inter-cloud migration as simple as changing airlines would help the entire industry to quickly adopt the cloud without worrying about any lock-in fears. In fact by having standard APIs for IaaS would help PaaS expl...
NHK, Japan Broadcasting, will feature the upcoming @ThingsExpo Silicon Valley in a special 'Internet of Things' and smart technology documentary that will be filmed on the expo floor between November 3 to 5, 2015, in Santa Clara. NHK is the sole public TV network in Japan equivalent to the BBC in the UK and the largest in Asia with many award-winning science and technology programs. Japanese TV is producing a documentary about IoT and Smart technology and will be covering @ThingsExpo Silicon Valley. The program, to be aired during the peak viewership season of the year, will have a major impac...
SYS-CON Events announced today that ProfitBricks, the provider of painless cloud infrastructure, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. ProfitBricks is the IaaS provider that offers a painless cloud experience for all IT users, with no learning curve. ProfitBricks boasts flexible cloud servers and networking, an integrated Data Center Designer tool for visual control over the cloud and the best price/performance value available. ProfitBricks was named one of the coolest Clo...
Organizations already struggle with the simple collection of data resulting from the proliferation of IoT, lacking the right infrastructure to manage it. They can't only rely on the cloud to collect and utilize this data because many applications still require dedicated infrastructure for security, redundancy, performance, etc. In his session at 17th Cloud Expo, Emil Sayegh, CEO of Codero Hosting, will discuss how in order to resolve the inherent issues, companies need to combine dedicated and cloud solutions through hybrid hosting – a sustainable solution for the data required to manage I...
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Bradley Holt, Developer Advocate at IBM Cloud Data Services, will demonstrate techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user experience, both offline and online. The focus of this talk will be on IBM Cloudant, Apa...
WebRTC is about the data channel as much as about video and audio conferencing. However, basically all commercial WebRTC applications have been built with a focus on audio and video. The handling of “data” has been limited to text chat and file download – all other data sharing seems to end with screensharing. What is holding back a more intensive use of peer-to-peer data? In her session at @ThingsExpo, Dr Silvia Pfeiffer, WebRTC Applications Team Lead at National ICT Australia, will look at different existing uses of peer-to-peer data sharing and how it can become useful in a live session to...
As a company adopts a DevOps approach to software development, what are key things that both the Dev and Ops side of the business must keep in mind to ensure effective continuous delivery? In his session at DevOps Summit, Mark Hydar, Head of DevOps, Ericsson TV Platforms, will share best practices and provide helpful tips for Ops teams to adopt an open line of communication with the development side of the house to ensure success between the two sides.
SYS-CON Events announced today that IBM Cloud Data Services has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IBM Cloud Data Services offers a portfolio of integrated, best-of-breed cloud data services for developers focused on mobile computing and analytics use cases.
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.