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PDF Scripting in Java: Languages, Frameworks, and Patterns

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This approach brings more transparency in terms of knowing parameter types and returning the value type.

Scripting in Java™: Languages, Frameworks, and Patterns

Despite the fact that using scripting engines is quite simple, if you have a lot of scripts in your codebase, you may encounter some performance problems. As an example, you can use Groovy templates for reporting and run reports at the same time. For example, in the CUBA framework, there is a pretty sophisticated Scripting engine that implements features to improve script implementation and execution such as:. All of these improve performance and usability, but still, those are low-level APIs for creating parameter maps, fetching script text, etc. Therefore, we still need to group them into high order modules to use scripting efficiently in an application.

You can find a lot of useful classes in org. There are evaluators, factories, and all the tools you need to build your own scripting support. Aside from low-level APIs, the Spring framework has an implementation that should simplify dealing with scripts in your application. You can define beans implemented in dynamic languages as described in the documentation. All you need to do is to implement a class using a dynamic language like Groovy and describe a bean in the configuration XML like this:.

After that, you can inject the Messenger bean into your application classes using the XML config. This approach looks good, but you, as a developer, should implement full-fledged classes for your beans if you want to utilize all the power of dynamic language support. Real-life scripts may be pure functions; therefore, you need to add some extra code to your script just to keep it compatible with Spring.

So, everything has its price, and when you add scripting to your application, you may meet some challenges:. Discoverability — if something goes wrong in a calling script, it's quite hard to find the actual point in the source code. We should be able to find all script invocation points easily in our IDE. Transparency — writing a scripted extension is not a trivial thing, as there is no information about variables sent to the script and no information about the result it should return.

In the end, scripting can be only done by a developer and only looking into the sources. Test and Updates — deploying updating a new script is always dangerous. There is no way to rollback and no tooling to test it before production. It seems like hiding scripted method calls under regular Java methods may resolve most of these challenges. And what if we go one step further and hide all calls to a scripting engine, parameter creation, etc. The idea is pretty simple and should be familiar to all developers who worked with the Spring framework. We just create a Java interface and link its methods to the scripts somehow.

We will likely need a class-level annotation that will help us to detect script repository interfaces and construct a special Spring bean for them. A method-level annotation will help us to link the method to its scripted implementation. And it would be nice to have a default implementation for the method that is not a simple stub but a valid part of the business logic. It will work until we implement an algorithm developed by a business analyst. And the business analyst says that we can safely assume that a 10 percent discount can be provided for all registered customers by default.

We may think about the following code concept for this case:. And when it comes to a proper discounting algorithm implementation, the Groovy script will look like this:. An ultimate goal for all this is to let a developer implement an interface and the discounting algorithm script only. The scripting solution should do all the magic for you — when the method is invoked, intercept the invocation, find and load the script text, evaluate it, and return the result or execute default method if the script text is not found.

The ideal usage should look similar to this:. The script call is readable and the way it is invoked should be familiar to any Java developer. Those were the ideas used to create a library for script repository implementation using the Spring framework. The library has facilities for script text load from different sources and evaluation as well as APIs that allow a developer to implement extensions for the library if needed.

And for this annotation, you need to specify the array of package names that should be scanned similarly to JPA repositories.


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And the default implementation for the scripted methods is supported, of course. All components of the solution are displayed in the diagram below. Blue shapes are related to the application code and white ones to the library.

Spring beans are marked with the Spring logo. After script evaluation, the result is returned to a calling service. Those names should be used in the script since the Java compiler erases actual parameter names on the compilation. You can omit those annotations. By default, the library has providers that can read Groovy and JavaScript files from the file system and JSRbased evaluators for both script languages. There are a lot of well-known pros and cons for using such an approach, like great flexibility to define business logic at runtime and save a massive amount of time on redeployment.

This avoids the impossibility to perform comprehensive testing and, hence, unpredictable problems with security, performance issues, and so on. The ways of scripting will be discussed further and might be helpful both for those who already decided to stick with scripting plugins in their Java application or those just now thinking about adding it to their code. Sometimes, you might even go a bit further. All methods will contain parameter mapping, script text loading logic, and a script evaluation engine invocation similar to this:.

This approach brings more transparency in terms of knowing parameter types and returning the value type. Despite the fact that using scripting engines is quite simple, if you have a lot of scripts in your codebase, you may encounter some performance problems.

As an example, you can use Groovy templates for reporting and run reports at the same time. For example, in the CUBA framework, there is a pretty sophisticated Scripting engine that implements features to improve script implementation and execution such as:. All of these improve performance and usability, but still, those are low-level APIs for creating parameter maps, fetching script text, etc.

Top five scripting languages on the JVM | InfoWorld

Therefore, we still need to group them into high order modules to use scripting efficiently in an application. You can find a lot of useful classes in org. There are evaluators, factories, and all the tools you need to build your own scripting support. Aside from low-level APIs, the Spring framework has an implementation that should simplify dealing with scripts in your application.

You can define beans implemented in dynamic languages as described in the documentation. All you need to do is to implement a class using a dynamic language like Groovy and describe a bean in the configuration XML like this:.

Top five scripting languages on the JVM

After that, you can inject the Messenger bean into your application classes using the XML config. This approach looks good, but you, as a developer, should implement full-fledged classes for your beans if you want to utilize all the power of dynamic language support. Real-life scripts may be pure functions; therefore, you need to add some extra code to your script just to keep it compatible with Spring. So, everything has its price, and when you add scripting to your application, you may meet some challenges:. Discoverability — if something goes wrong in a calling script, it's quite hard to find the actual point in the source code.

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We should be able to find all script invocation points easily in our IDE. Transparency — writing a scripted extension is not a trivial thing, as there is no information about variables sent to the script and no information about the result it should return. In the end, scripting can be only done by a developer and only looking into the sources. Test and Updates — deploying updating a new script is always dangerous. There is no way to rollback and no tooling to test it before production. It seems like hiding scripted method calls under regular Java methods may resolve most of these challenges.

And what if we go one step further and hide all calls to a scripting engine, parameter creation, etc. The idea is pretty simple and should be familiar to all developers who worked with the Spring framework. We just create a Java interface and link its methods to the scripts somehow. We will likely need a class-level annotation that will help us to detect script repository interfaces and construct a special Spring bean for them. A method-level annotation will help us to link the method to its scripted implementation. And it would be nice to have a default implementation for the method that is not a simple stub but a valid part of the business logic.

It will work until we implement an algorithm developed by a business analyst. And the business analyst says that we can safely assume that a 10 percent discount can be provided for all registered customers by default.


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  • We may think about the following code concept for this case:. And when it comes to a proper discounting algorithm implementation, the Groovy script will look like this:.

    An ultimate goal for all this is to let a developer implement an interface and the discounting algorithm script only. The scripting solution should do all the magic for you — when the method is invoked, intercept the invocation, find and load the script text, evaluate it, and return the result or execute default method if the script text is not found.

    The ideal usage should look similar to this:. The script call is readable and the way it is invoked should be familiar to any Java developer.