Analysis Engine - Documentation

The analysis engine is the 'brain' of Jemos Clanker. Its main role is to analyze a set of Java sources and to make available the results of the analysis process to its clients. Those data are made available through bean-like objects that contain either data and operations to retrieve the required information. The most important of those objects, is identified by the Amplimet, represented by the class and whose contract is defined by the interface. An Amplimet is contained within a Thapter, identified by the class and whose contract is defined by the interface. A thapter is the main 'analysis engine object' since it's the object which gets initialized with the list of sources to analyze and filters to apply and which contains the business methods to start the analysis engine.

Analysis Engine: main components

At high level, there are few major components, shown in the picture below and about which follows a description.

  • Thapter. This is the main object in the analysis engine. Its responsibilities are to coordinate the analysis activities and to maintain an Amplimet (see below), which contains the analysis results. A Thapter needs to be initialized with a Controller which in turn needs to be created with a Configuration object. Referring to the 'Well of Echoes' series, from which the Thapter takes the name, a Thapter is an alien construct that the heroin of this series made fly and then ever since became an important anspect in winning the war for humans.
  • Controller. A controller in the book series is a special artifact that artisans can make move things thanks to the power of crystals, by using the 'aura' manifested by those crystals. In this framework as in the book, a controller is used to give 'life' to a Thatper (and Clankers for that matter) and in order to be of any use, it must be created using a configuration object.
  • Configuration. A configuration object is created as first step when using Jemos Clanker. It can be initialized with info like: process/don't process Javadocs; process/don't process Annotations; I want only classes with this particular Javadoc or Annotation; this is the list of sources Clanker has to analyze, etc.
  • Crystal. A crystal is an object containing all possible filters that Jemos Clanker will use in order to 'filter' the analysis results. The approach to set up filters is to create the desired filters first, to set those filters in a Crystal object and to set the Crystal object in a Configuration object.
  • Filter. Filters are used to filter information. Currently only three types of filters are supported, but nothing avoids you from creating your own. All you need to do is to create a class which implements the Filter interface. The filters currently supported allow you to select only classes with specific Javadoc tags at class, method and instance variable level and/or to select only those classes with specific Annotation names at class, method and instance variable level. You can use those filters separately or together. Jemos Clanker will handle the process behind the scenes, returning those classes that at least match a filter criteria. It is also possible to ask Jemos Clanker to return all classes, even if filters were specified: in this case bean-like objects encapsulating Class, Method, Instance Variables, etc will be returned but only with the information defined in the filters (for the concepts of Class, Method, etc. please refer to the 'Component' section below).
  • Component. A component is another central concept in Jemos Clanker. Each object implementing the 'Component' interface represents a logical part in a Java source program. The logical parts currently supported are: Classes, Methods, Instance Variables, Annotations, Javadoc comments (at various level, like class, method and instance variable), Packages, Local variables. When Jemos Clanker analysis engine runs, it fills one or more of those components with the relevant information that will then be available in a bean-like structure. The component are related in a parent-child structure, so that a Package can have children (typically classes), Classes can have children (methods, instance variables, other classes) and so on. At runtime, Jemos Clanker fills an Amplimet with the list of Packages, and then delegates to Lyrinx the job of analyzing parts of source and to create the related bean-like structures, flagging each one with its parent. It's important to note that each Component, at the end of the process, must contain attributes identifying the information specific to that component, be these Java source info (like the list of parameters of exceptions for a method), Javadoc info (like the list of Javadoc tags with their values), Annotation info (like the annotation name, their attributes and values). This makes very easy then to process the results in a script-based framework (like Jelly for instance). In few words the analysis engine is responsible for filling up nicely all the required information, whereas the result engine is responsible to offer a set of tags that make easy to launch the analysis tool and to use its results afterwards.
  • Amplimet. An amplimet is the object which external clients will use when the analysis engine has finished the process. In the book series, an amplimet is an extremely precious crystal, which has been in a mine for thousands of years waiting for someone to discover it and that, apparently is capable of guiding events. Similarly, in this framework an Ampliment is the most precious object available at the end of the process, since it's possible to retrieve the list of analyzed packages from it and then, from each package is possible to retrieve the list of classes and so on. The Amplimet offers also methods to maintain the registry of components. To facilitate the programmatic use of the parent/child relationship at runtime, each component (except from a Package) must be created setting in its state the unique id of its parent (we assumed the hashcode of the parent object to be this unique id).

Analysis engine: starting the analysis process

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Here follows a brief overview of the activities necessary to start the analysis process. Please note that setting the list of Java source to analyze in the ConfigurationImpl object is mandatory but defining filters (and therefore a Crystal object) is not. Additionally, users can specify whether (if they set one or more filters) they want in return only the classes matching those filters, or all the classes with only the filtered information.

The takeOff() method of the Thapter class starts the analysis process. Those are the activities that a client will need to perform in order to initialize and start the analysis engine:

  • Create a Configuration object. The default implementation is and the contract is defined by the interface.
  • Sets a collection of paths (represented as String objects) pointing to Java sources. This is the list of Java sources that the analysis engine will analyze. This step is mandatory, since the analysis wouldn't make sense if there were no source to analyzie :)
  • The client can set a flag to tell the analysis engine if it should process Javadocs. The default is true and this is not a mandatory attribute.
  • The client can set a flag to tell the analysis engine if it should process Annotations. The default is true and this is not a mandatory attribute.
  • Clients can specify one or more Javadoc/Annotation filters, by creating objects of the filter classes, whose contract is defined by the interface. The only filters supported at the moment are: Javadoc, Annotation and Name filters. These are represented by classes located in the package
  • If any filter was created, then clients should create an instance of the class, and set those filters as attributes in the Crystal class. The Crystal class then should be set as attribute in the ConfigurationImpl object. object in the Configuration object. Filters are not mandatory and if not specified, all Javadocs and Annotations will be taken into consideration. Additionally, if filters were set, clients have got the opportunity to ask the analysis engine if they want it to return all classes (although only with the data matching the filters) of if they want it to return only the classes matching at least one of the matching filters. This is accomplished by setting the returnType attribute of the Crystal object, represented by an enumeration (a new concept in Java 5). The possible values for this attributes are either: ALL or CLASSES, where the former asks for all classes (although the Javadocs and Annotations contained within will match the filters selection) and the latter asks to return only the classes for which at least one match was found.
  • Create a Controller, represented by an instance of the class, whose contract is defined by the interface. A controller must be initialized with the instance of a ConfigurationImpl created above
  • Create an instance of the class, whose contract is defined by the interface, initializing it with the ControllerImpl instance created above.
  • Starting the Thapter by invoking its takeOff() method

Below is an example of how the HeartBitTag class initializes and invokes the analysis process, following the steps identified above:

		//Prepares the configuration object
		ConfigurationImpl config = new ConfigurationImpl();
		//Sets the filters if any were set up by the children
		Crystal crystal = new Crystal();
		//javadocFilter is an instance of the CommentFilter class
		if (null != javadocFilter) {
		//annotationFilter is an instance of the AnnotationFilter class
		if (null != annotationFilter) {
		//Sets the returnType attribute of the Crystal class
		if (getType().toLowerCase().equals("class")) {
		    //I want only classes matching the filters
		} else {
			//Get me all classes but the Javadoc/Annotation/Class names
			//must match the filters
		//Sets the crystal object in the configuration object
		//Sets the sources to analyze in the configuration object
		//Sets the flag whether to process Javadoc and/or Annotations
		try {
			//Creates the controller and initializes it with the
			//configuration object
			Controller controller = new ControllerImpl(config);
			//Prepares the Thapter and initializes it with the controller object
			Thapter thapter = new ThapterImpl(controller);
			buff.append("[HeartBit]Launching the thapter...\n");
			//Launches the thapter
			buff.append("[HeartBit]Thapter ended the execution. Retrieving the amplimet...\n");
			//The Thapter has filled the entry point for the result in the Amplimet
			Amplimet amplimet = thapter.getAmplimet();
			//Here it retrieves the packages from the Ampliment and
			//from each package it retrieves the list of classes
			Package p = null;
			for (Component pkg: packages) {
				p = (Package)pkg;
				buff.append("[HeartBit]Package: " + p.getPackageName());
			//Sets the data in the context and invokes the output script
			getContext().setVariable("classes", this.getClasses());
			getContext().runScript(outputF, output);
		} catch (ConfigurationException e) {
			throw e;
		} catch (ThapterException e) {
			throw e;
		} catch (IOException e) {
			throw e;

How does the analysis process work?

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The analysis process delegates to the Java Compiler API the parsing and externalization of the Java source files. The method which starts the analysis process is takeOff() which simply invokes two methods:

  • wakeTheAmplimet
  • applyFilters

The wakeTheAmplimet() method is shown below:

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As mentioned earlier, Jemos Clanker delegates to the JDK parser the job of parsing a Java source and to make available objects each one identifying a logical part of a Java source file. The JDK parser divides a Java source in its logical parts (the imports, the package declaration, the class declarations, method and parameters, exceptions, annotations, etc.). Each one of these logical parts is set in a class child of the class. Below you can see a class diagram of some of the children of the Tree class (the diagram is a bit messy because I had to squeeze all the Tree objects so as to have all of them in one page):

Where a class gets processed: the fillTheAmplimet() method

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All the wakeTheAmplimet method does is to loop through each of the Java source paths set in the sources collection set in the ConfigurationImpl object. For each of these sources, it creates a object which is then converted in a java.nio.ByteBuffer object. This ByteBuffer object is then passed as argument to the constructor of the class which in turn is passed as argument to the class in order to obtain a new object. The Parser is actually the class which performs the source analysis and then externalizes a class in its logical parts in a object with all its sub-trees. Once the Tree object is created, which happens for each Java source, the fillTheAmplimet(Tree) method is invoked. Below there is a sequence diagram which illustrates what this method does.

Here what happens:

  • If a Package instance already exist (packages are unique), we just use it, otherwise a new one is created and set in the Amplimet. The Amplimet maintains a collection of Packages being processed, that's why it's the main object returned by the analysis process. Clients should iterate over the collection of packages and for each package should retrieve the children (classes) and so on in a recursive way until all the components of interest have been dealt with.
  • The fillTheAmplimet(TopLevel Tree) method receives as parameter a TopLevel object (static inner class of, containing an 'objectized' version of a Java class. By 'objectized' I mean a division of a class' logical parts into subclasses of Tree. Those logical parts encapsulate Javadoc comments, the different elements of a class (methods, instance variables, inner classes, etc), Annotation definitions, etc.
  • The method loops through all the different parts of the Tree and delegates their analysis and processing to ad-hoc processors (Lyrinx). The order in which Tree components are contained in the TopLevel object is the following:

    • Package definitions
    • Import declarations
    • Javadoc comments
    • Class members (class, method, instance variable definitions)

    We've already seen how Packages are processed. Since this method is invoked for each Java source, we may be quite relaxed at the idea of storing the list of imports and Javadoc definitions in the ThapterImpl class itself, so that processors will be able to refer to it during the processing. The execution of the fillTheAmplimet method is not thread-safe. This means that it is not possible to invoke the same method for two different classes simultaneously. Each execution has to do with one class at the time, since class-specific information like imports and Javadocs are stored as instance variables. Kept the ordering process correct though, this approach works very nicely, since an instance of ThapterImpl is passed as parameter to each Tree processor.

    So this method stores all the imports in a collection declared as instance variable (which gets cleared before each invocation); it then delegates to the Javadoc processor the Javadoc processing (the processor will store as instance variables of ThapterImpl the class, methods and instance variables Javadocs for other processor to look at, and similarly to what happened with imports, cleared before each iteration). Once package, class and Javadocs have been 'externalized' to Javabean-like structures, this method retrieves the right processor for the Tree being processed (in this case a ClassLyrinx) and delegates to this processor the class' externalization. At the end of the processing of the ClassLyrinx class, a object has been filled with all class-related and class-members' related information and it is then added as child of the Package object through the addComponent(component) method.

Applying filters

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Filters are used in one of two ways:

  • To restrict the Javadoc/Annotation info returned by the analysis process
  • To select only those classes which contain at least one matching criteria for Javadoc or Annotation or name
Filters are specified by creating instances of classes implementing the interface. Currently Jemos Clanker supports only three kind of filters:

  • Javadoc filters
  • Annotation filters
  • Name filters
Filters are specified before starting the analysis process, by creating filter objects, a crystal object and by setting those filters as instance variables in a crystal. Then the crystal is set as instance variable of the ConfigurationImpl class so that it participates in the Thapter initialization. You can refer to the above paragraph to refresh how filters and the Crystal object are created.

Here follows how the Thapter.applyFilters() method works:

Here what happens:

  • The first thing the method determines is if it has to apply class exclusion. If the client creates a Crystal object and set the returnType instance variable to the value of (which is an enumeration value) it means that class exclusion has been turned on. In this case, only the classes matching at least one filter criteria will be returned. If class exclusion has been turned off then all classes will be returned, but those will contain only the values specified in the filters.
  • The method determines if any Javadoc and/or Annotation filters were setup, setting some boolean flags to indicate that. If no filters were applied, it returned immediately.
  • The method then retrieves all the analyzed packages from the Amplimet object filled in during the execution of the wakeTheAmplimet() method. Since the appliFilters() method is invoked at the end of the analysis process, the Amplimet contains all the Java sources externalized.
  • For each Package, the method retrieves all classes and apply Javadoc and/or Annotation filters, depending on which of those were set up. The result of applying those filters is that Javadocs and/or Annotations not matching the filters will be removed from the collections containing them. If class exclusion was turned on, the method checks if any values matching the filters have been found. If this is not the case, the class is marked for deletion (i.e. it will be removed from the value returned to the client).
  • Similarly to what the method performed with the Package happens also for each class object. For each one of them in fact, the method retrieves all methods and instance variables and applies the filters with the same logic explained in the point above. The only difference here is that, even if class exclusion was turned on but the filter at class level found a valid class (i.e. at least one matching criteria), even if the method and/or instance variable filtering haven't produced any results the class will be kept and returned to the client.
  • At the end of the process, if the class has to be removed, this is removed from the collection of the Package children and from the registry of components maintained in the Amplimet.