Introduction

The Google Web Toolkit (GWT) compiler has been a critical tool for developers who prefer writing front-end applications in Java. However, one significant challenge when using GWT is the lengthy compile times, especially as your project scales. Optimizing the GWT compiler can significantly streamline development processes and enhance productivity. This article discusses various strategies to speed up the GWT compiler, providing technical explanations and examples where applicable.

Understanding GWT Compilation

The GWT compiler translates Java code into optimized JavaScript. This process involves several steps including type-checking, source-to-source code transformations, and JavaScript optimizations. However, three main phases often contribute to slower performance:

1. Permutation Compiling: GWT compiles your application into several JavaScript permutations to support different browsers.
2. JavaScript Output: Large codebases lead to larger JavaScript outputs, which take longer to compile.
3. Dependencies and Libraries: Including many libraries can increase compilation times as each additional library increases the overall workload.

Strategies to Speed Up GWT Compilation

1. Use the Super Dev Mode

Switch from Classic Dev Mode to Super Dev Mode. Super Dev Mode offers incremental compilation, which is quicker because it reduces the workload by recompiling only the modified classes. This yields faster feedback during the development phase.

mvn gwt:run-codeserver

2. Optimize Permutations

Reducing the number of permutations can lead to substantial improvements in compilation speed without compromising too much on browser support. You can achieve this by setting specific user agents in your module XML file.

<set-property name="user.agent" value="safari1, ie8, ie9, gecko1_8" />

Avoid unnecessary permutations for browsers not targeted by your application. Another helpful option is utilizing collapse-all-properties which can minimize permutations.

3. Modularize the Application

Modularizing your GWT application means splitting the monolithic app into smaller, more manageable modules. This allows each module to be compiled separately, facilitating parallel compilation.

4. Use Incremental Compilation

Whenever possible, use incremental builds instead of full recompiles. Tools like mvn can help with incremental builds, where only changed components are recompiled.

mvn clean install -Dgwt.compiler.incremental=true

5. Optimize Your Java Code

Reducing the complexity of your Java code can lead to faster compilation. This includes:

• Refactoring Code: Keep your code clean and refactor large classes.
• Removing Unused Code: Using tools such as ProGuard to eliminate dead code can reduce compile times and output size.
• Using GWT Compiler Flags: Optimize -optimize, -ea, and -XdisableAggressiveOptimization flags to the compiler command line for different phases of your development.

6. Upgrade Your Hardware

A simple but effective method is ensuring your hardware is up to the task. Faster CPUs and increased RAM can provide significant improvements in compilation times. As GWT compilation is CPU-bound, consider prioritizing CPU speed.

7. Parallelize Compilation

Running multiple compilation threads can enhance performance, especially on multi-core processors. Use the -localWorkers flag, which dictates the number of parallel worker threads.

mvn gwt:compile -Dgwt.compiler.localWorkers=4

Summary Table

Conclusion

Enhancing the speed of your GWT compiler involves a multi-pronged approach. By optimizing permutations, using incremental builds, and upgrading your hardware, among other techniques, you can significantly decrease compile times and improve development efficiency. Applying these strategies will ensure that your GWT applications are compiled quickly, keeping you agile in your development workflow.