add convenience methods for field access and modification handlers

src/example/groovy/org/jdiscript/example/HelloWorldExample.groovy

@@ -11,29 +11,31 @@ import com.sun.jdi.VirtualMachine;
 import com.sun.jdi.request.ClassPrepareRequest;
 import com.sun.jdi.request.StepRequest
 
+// The HelloWorld java example code prints out "Hello, <someone>" twice
+// for 3 different values of <someone>. This scripts changes the second
+// printout for each to "Hello, Groovy".
+
 String OPTIONS = """
-    -cp ./target/classes/
+    -cp ../../../build/jdiscript.jar
 """
 String MAIN = "org.jdiscript.example.HelloWorld"
 VirtualMachine vm = new VMLauncher(OPTIONS, MAIN).start()
 
 JDIScript j = new JDIScript(vm);
-j.run({
-    j.classPrepareRequest({
-         def field = it.referenceType().fieldByName("helloTo")
-         j.accessWatchpointRequest(field, {
-              def obj = it.object()
-              j.stepRequest(it.thread(),
-                            StepRequest.STEP_MIN,
-                            StepRequest.STEP_OVER, {
-                   StringReference alttobe = it.virtualMachine().mirrorOf("Groovy")
-                   it.request().disable()
-                   obj.setValue(field, alttobe)
-                } as OnStep).enable()
-          } as OnAccessWatchpoint).enable()
-     } as OnClassPrepare).addClassFilter("org.jdiscript.example.HelloWorld")
-                         .enable()
-} as OnVMStart)
+
+j.onFieldAccess("org.jdiscript.example.HelloWorld", "helloTo", {
+    def obj = it.object()
+    def field = it.field()
+    j.stepRequest(it.thread(),
+                  StepRequest.STEP_MIN,
+                  StepRequest.STEP_OVER, {
+        StringReference alttobe = j.vm().mirrorOf("Groovy")
+        it.request().disable()
+        obj.setValue(field, alttobe)
+    } as OnStep).enable()
+} as OnAccessWatchpoint)
+
+j.run()
 
 
 

src/main/java/org/jdiscript/JDIScript.java

@@ -11,7 +11,7 @@
 import org.jdiscript.requests.*;
 
 import com.sun.jdi.*;
-import com.sun.jdi.event.LocatableEvent;
+import com.sun.jdi.event.*;
 import com.sun.jdi.request.*;
 
 /**
@@ -33,6 +33,10 @@
  *    Runs the associated VM by setting up and starting the jdiscript
  *    {@link DebugEventDispatcher} and {@link EventThread}.
  *  </li>
+ *  <li>
+ *    Provides convenience methods for specifying handlers for field
+ *    access and modification.
+ *  </li>
  * </ul>
  */
 public class JDIScript {
@@ -539,4 +543,69 @@ public void printTrace(LocatableEvent event, String msg, PrintStream ps) {
                        "could not retrieve frames **");
         }
     }
+
+    /**
+     * Shortcut for the common pattern of responding to field accesses.
+     * <p>
+     * Builds a {@link ClassPrepareRequest}, filters it for the given
+     * class name, and adds an {@link OnClassPrepare} handler that
+     * creates an {@link AccessWatchpointRequest} for the given field name.
+     * Any field accesses are in turn handled by the given handler.
+     * <p>
+     * TODO: what should this return?
+     *
+     * @param className  A class name suitable for use by
+     *                   {@link ClassPrepareRequest#addClassFilter(String)}
+     * @param fieldName  A field name suitable for use by
+     *                   {@link ReferenceType#fieldByName(String)}.  Must be
+     *                   a field belonging to all classes matched by className.
+     * @param handler    The callback to execute when the field is accessed.
+     */
+    public void onFieldAccess(final String className,
+                              final String fieldName,
+                              final OnAccessWatchpoint handler) {
+        classPrepareRequest()
+            .addClassFilter(className)
+            .addHandler(new OnClassPrepare() {
+                    public void classPrepare(ClassPrepareEvent ev) {
+                        Field field = ev.referenceType().fieldByName(fieldName);
+                        accessWatchpointRequest(field, handler)
+                            .enable();
+                    }
+                })
+            .enable();
+    }
+
+    /**
+     * Shortcut for the common pattern of responding to field modifications.
+     * <p>
+     * Builds a {@link ClassPrepareRequest}, filters it for the given
+     * class name, and adds an {@link OnClassPrepare} handler that
+     * creates a {@link ModificationWatchpointRequest} for the given field name.
+     * Any field modifications are in turn handled by the given handler.
+     * <p>
+     * TODO: what should this return?
+     *
+     * @param className  A class name suitable for use by
+     *                   {@link ClassPrepareRequest#addClassFilter(String)}
+     * @param fieldName  A field name suitable for use by
+     *                   {@link ReferenceType#fieldByName(String)}.  Must be
+     *                   a field belonging to all classes matched by className.
+     * @param handler    The callback to execute when the field is modified.
+     */
+    public void onFieldModification(final String className,
+                                    final String fieldName,
+                                    final OnModificationWatchpoint handler) {
+        classPrepareRequest()
+            .addClassFilter(className)
+            .addHandler(new OnClassPrepare() {
+                    public void classPrepare(ClassPrepareEvent ev) {
+                        Field field = ev.referenceType().fieldByName(fieldName);
+                        modificationWatchpointRequest(field, handler)
+                            .enable();
+                    }
+                })
+            .enable();
+    }
+
 }