在运行时获取变量的值

Question

I'm currently working on an Eclipse Plug-in. The plugin should read a java class and get the value of a certain variable at runtime .

Example of a java class:

public class MyClass {

 private int aVariable;

public int getaVariable() {
    return aVariable;
}

public void setaVariable(int aVariable) {
    this.aVariable = aVariable;
}

private int doSomethinng (){
    setaVariable(10);
    int x = getaVariable();
    return x;
}

}

Now my plugin should get the value of the variable x at RUNTIME and print it on the eclipse console(first). To read this class i created an Eclipse plugin "Hello World Commands":

import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.core.resources.IProject;
import org.eclipse.core.resources.IWorkspace;
import org.eclipse.core.resources.IWorkspaceRoot;
import org.eclipse.core.resources.ResourcesPlugin;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.jdt.core.ICompilationUnit;
import org.eclipse.jdt.core.IJavaProject;
import org.eclipse.jdt.core.IMethod;
import org.eclipse.jdt.core.IPackageFragment;
import org.eclipse.jdt.core.IPackageFragmentRoot;
import org.eclipse.jdt.core.IType;
import org.eclipse.jdt.core.JavaCore;
import org.eclipse.jdt.core.JavaModelException;
import org.eclipse.jface.text.Document;

public class SampleHandler extends AbstractHandler {

  public Object execute(ExecutionEvent event) throws ExecutionException {
    // Get the root of the workspace
    IWorkspace workspace = ResourcesPlugin.getWorkspace();
    IWorkspaceRoot root = workspace.getRoot();
    // Get all projects in the workspace
    IProject[] projects = root.getProjects();
    // Loop over all projects
    for (IProject project : projects) {
      try {
        printProjectInfo(project);
      } catch (CoreException e) {
        e.printStackTrace();
      }
    }
    return null;
  }

  private void printProjectInfo(IProject project) throws CoreException,
      JavaModelException {
    System.out.println("Working in project " + project.getName());
    if (project.isNatureEnabled("org.eclipse.jdt.core.javanature")) {
      IJavaProject javaProject = JavaCore.create(project);
      printPackageInfos(javaProject);
    }
  }

  private void printPackageInfos(IJavaProject javaProject)
      throws JavaModelException {
    IPackageFragment[] packages = javaProject.getPackageFragments();
    for (IPackageFragment mypackage : packages) {
      if (mypackage.getKind() == IPackageFragmentRoot.K_SOURCE) {
        System.out.println("Package " + mypackage.getElementName());
        printICompilationUnitInfo(mypackage);

      }

    }
  }

  private void printICompilationUnitInfo(IPackageFragment mypackage)
      throws JavaModelException {
    for (ICompilationUnit unit : mypackage.getCompilationUnits()) {
      printCompilationUnitDetails(unit);

    }
  }

  private void printIMethods(ICompilationUnit unit) throws JavaModelException {
    IType[] allTypes = unit.getAllTypes();
    for (IType type : allTypes) {
      printIMethodDetails(type);
    }
  }

  private void printCompilationUnitDetails(ICompilationUnit unit)
      throws JavaModelException {
    System.out.println("Source file " + unit.getElementName());
    Document doc = new Document(unit.getSource());
    System.out.println("Has number of lines: " + doc.getNumberOfLines());
    printIMethods(unit);
  }

  private void printIMethodDetails(IType type) throws JavaModelException {
    IMethod[] methods = type.getMethods();
    for (IMethod method : methods) {

      System.out.println("Method name " + method.getElementName());
      System.out.println("Signature " + method.getSignature());
      System.out.println("Return Type " + method.getReturnType());

    }
  }
} 

I can get information package, number of lines, method's name etc.., but the problem is i want to print the value of a variable AT RUNTIME ! Can you please help me?

Answer 1

This is a classic static vs. dynamic analysis problem. Currently your Eclipse plugin is viewing the projects statically because the projects are not being executed.

For your example MyClass there is no associated main method so you can't actually run the project anyway. Without adding a driver (main method with calls to this class) dynamic analysis is not going to be possible. However if you went down the dynamic analysis route you might consider instrumenting MyClass with logging utilities to record the runtime values of aVariable (which may be more than one value!).

As for static analysis, any complete answer would have to conservatively report that aVariable could be any integer value because the setaVariable method is publicly accessible and could be passed any integer value. If we restricted the potential call targets to only doSomething then you could report that 10 is the only possible value. Finally if you did have other code that goes along with this class you could start from all valid program entry points (main methods or application specific lifecycle entry points) and do some analysis to find the places where doSomething and setaVariable are called from the within the rest of the project. You would then need to backtrack along data flow and control flow paths and perform some symbolic execution to find the potential runtime values (again there could be more than one!).

Consider the following main method as a driver.

public static void main(String[] args){
    Random rnd = new Random();
    MyClass c = new MyClass();
    if(rnd.nextBoolean()){
        c.setaVariable(100);
    } else {
        c.doSomething();
    }
}

What is the runtime value of aVariable ? It could have two values, 10 or 100 . This is a tricky problem and a lot of research has gone into it. The more precise you try to solve it the more headaches you will get.