Discovering Valid Java Main Methods
The Toolbox Commons project defines an Analyzer
interface that encapsulates the logic for traversing a program graph to extract an "envelope" (a subgraph that is either empty if a property is satisfied or non-empty containing the necessary information to locate the violation of the property). Analyzers encapsulate their descriptions, assumptions, analysis context, and analysis logic. Of course you can define your own "Analyzer" simply by writing a program with your analysis logic, but we find this abstraction helps keep code organized when contributing to a toolbox project.
Contents
Development Process
Let's start off with a simple analysis goal. Write an analyzer that discovers all valid Java main methods in a program. We might want to discover main methods to locate developer test code or alternate entry points into an application.
Step 1) Understanding the problem
The first step is always to ask yourself if you really understand the problem. Now is the time to do some background research. Can main methods be located in inner classes? Can main methods be final? Can main methods return anything other than void? This blog has enumerated through several variations on main methods.
Step 2) Developing test cases
A little upfront work to create a decent test set will likely save you a lot of time in the development of your analyzer since you will be able to quickly identify the cases you are not handling correctly. For this tutorial we've already created an application with several test cases for you! Just checkout the https://github.com/EnSoftCorp/LearningAtlas repository and import the MainMethodTestCases
Eclipse project into your workspace. Since you didn't have to go through the work of developing the test cases yourself, its probably a good idea to go through the test cases now. We have created several Java classes, each with a main method. The classes with valid main methods are in the com.example.valid
package, whereas the classes with invalid main methods are in the com.example.invalid
package.
Step 3) Create Analyzer
From the exercise of going through steps 1 and 2, we can now create a new Analyzer and document our assumptions (at least the assumptions we've made so far).
In the Starter Toolbox create a new class in the toolbox.analysis.analyzers
package. Name the class DiscoverMainMethods
and extend the com.ensoftcorp.open.toolbox.commons.analysis.Analyzer
base class.
Let's take this opportunity to fill out the information that we know so far. We learned that Java main methods must be public, static, void methods named "main" (case-sensitive). Main methods take a single parameter of a one-dimensional String array. The main method may optionally be marked as final, synchronized, or strictfp. After documenting this information, your analyzer should look something like the following.
package toolbox.analysis.analyzers; import com.ensoftcorp.atlas.core.query.Q; import com.ensoftcorp.open.toolbox.commons.analysis.Analyzer; public class DiscoverMainMethods extends Analyzer { @Override public String getName(){ return "Discover Main Methods"; } @Override public String getDescription() { return "Locates valid Java main methods."; } @Override public String[] getAssumptions() { return new String[]{"Main methods are methods.", "Main methods are case-sensitively named \"main\"", "Main methods are public.", "Main methods are static.", "Main methods return void.", "Main methods take a single String array parameter", "Main methods may be final.", "Main methods may have restricted floating point calculations.", "Main methods may be synchronized."}; } @Override protected Q evaluateEnvelope() { // TODO: Implement return null; } }
Step 4) Develop and Debug Analyzer Logic
The evaluateEnvelope
method is where we put our analysis logic. The Analyzer
base class defines a method getEnvelope
that lazily evaluates the result of your analysis defined in the evaluateEnvelope
method and caches the result for later. Future calls to getEnvelope
return the cached result.
We can run our analyzer on the Atlas shell by instantiating a new DiscoverMainMethods
object and calling the getEnvelope
method.
var analyzer = new DiscoverMainMethods() var envelope = analyzer.getEnvelope() show(envelope)
The show
method should fail here because our getEnvelope
currently returns null. We've broken out the steps to implement our analysis logic into five steps, but keep in mind there is more than one way to implement this analyzer! If you are ambitious, you could try stopping here and implementing your own analyzer then comparing your solution with ours.
Analysis Step 1) Select public static methods
Let's start off our implementation by making a set of all the public static methods we can find in the program graph. These three properties are all Atlas Tags so we can query for them directly. Node we use nodesTaggedWithAll
here instead of nodesTaggedWithAny
because we want nodes that are public and static and methods.
protected Q evaluateEnvelope() { // Step 1) select nodes from the index that are marked as public, static, methods Q mainMethods = Common.universe().nodesTaggedWithAll(Node.IS_PUBLIC, Node.IS_STATIC, Node.METHOD); return mainMethods; }
If we run our analyzer now, we should be returning all public static methods in the universe. Let's test it out. If you haven't already, save your DiscoverMainMethods.java
file. Now reload the Atlas Shell. Its important to reload the Atlas shell at this point because if you don't you will be running the version of DiscoverMainMethods
that was compiled the last time you reloaded the shell. After reloading the shell, run the following query.
show(new DiscoverMainMethods().getEnvelope())
After running the query, you will notice a Eclipse job progress monitor in the bottom right corner of the Eclipse window as shown below.
If you included Jar Indexing in your Atlas preferences, then this job will be very slow. This is because you are trying to display a very large graph! Displaying a large graph should be avoided, because it will be too large for a human to understand anyway. Let's cancel this job. Click on the the Eclipse job progress icon in the bottom right hand corner of the Eclipse window or open the Eclipse Progress view. Now click on the red cancel job button to the right of the task name to cancel the job as shown in the screenshot below.
Let's find out just how big that graph was. Run the following query in the Atlas Shell to count the number of nodes in the graph.
CommonQueries.nodeSize(new DiscoverMainMethods().getEnvelope())
Analysis Step 2) Select methods named "main"
TODO
Analysis Step 3) Select methods that return void
TODO
Analysis Step 4) Select methods that only take one parameter
TODO
Analysis Step 5) Select methods that take a String array
TODO
Final Implementation
public class DiscoverMainMethods extends Analyzer { @Override public String getName(){ return "Discover Main Methods"; } @Override public String getDescription() { return "Locates valid Java main methods."; } @Override public String[] getAssumptions() { return new String[]{"Main methods are methods.", "Main methods are case-sensitively named \"main\"", "Main methods are public.", "Main methods are static.", "Main methods return void.", "Main methods take a single String array parameter", "Main methods may be final.", "Main methods may have restricted floating point calculations.", "Main methods may be synchronized."}; } @Override protected Q evaluateEnvelope() { // Step 1) select nodes from the index that are marked as public, static, methods Q mainMethods = appContext.nodesTaggedWithAll(Node.IS_PUBLIC, Node.IS_STATIC, Node.METHOD); // Step 2) select nodes from the public static methods that are named "main" mainMethods = mainMethods.selectNode(Node.NAME, "main"); // Step 3) filter out methods that are not void return types mainMethods = mainMethods.intersection(Common.stepFrom(Common.edges(Edge.RETURNS), Common.types("void"))); // Step 4) filter out methods that do not take exactly one parameter Q paramEdgesInContext = appContext.edgesTaggedWithAny(Edge.PARAM).retainEdges(); // methods with no parameters will not have a PARAM edge Q methodsWithNoParams = mainMethods.difference(Common.stepFrom(paramEdgesInContext, Common.stepTo(paramEdgesInContext, mainMethods))); // methods with 2 or more params will have at least one edge with PARAMETER_INDEX == 1 (index 0 is the first parameter) Q methodsWithTwoOrMoreParams = Common.stepFrom(paramEdgesInContext, Common.stepTo(paramEdgesInContext, mainMethods).selectNode(Node.PARAMETER_INDEX, 1)); mainMethods = mainMethods.difference(methodsWithNoParams, methodsWithTwoOrMoreParams); // Step 5) filter out methods that do not take a String array // get the 1-dimensional String array type Q stringArrays = Common.stepFrom(Common.edges(Edge.ELEMENTTYPE), Common.typeSelect("java.lang","String")); Q oneDimensionStringArray = stringArrays.selectNode(Node.DIMENSION, 1); Q mainMethodParams = CommonQueries.methodParameter(mainMethods, 0); Q validMethodParams = mainMethodParams.intersection(Common.stepFrom(Common.edges(Edge.TYPEOF), oneDimensionStringArray)); mainMethods = Common.stepFrom(paramEdgesInContext, validMethodParams); return mainMethods; } }
Alternative Implementation
TODO