JavassistHelper.java

package org.slf4j.instrumentation;

import javassist.CtBehavior;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.Modifier;
import javassist.NotFoundException;
import javassist.bytecode.AttributeInfo;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.LocalVariableAttribute;

/**
 * Helper methods for Javassist functionality.
 * 
 */
public class JavassistHelper {

	/**
	 * Create a javaassist source snippet which either is empty (for anything
	 * which does not return a value) or a explanatory text around the $_
	 * javaassist return value variable.
	 * 
	 * @param method
	 *            descriptor of method
	 * @return source snippet
	 * @throws NotFoundException
	 */
	public static String returnValue(CtBehavior method)
			throws NotFoundException {

		String returnValue = "";
		if (methodReturnsValue(method)) {
			returnValue = " returns: \" + $_ + \".";
		}
		return returnValue;
	}

	/**
	 * determine if the given method returns a value, and return true if so.
	 * false otherwise.
	 * 
	 * @param method
	 * @return
	 * @throws NotFoundException
	 */
	private static boolean methodReturnsValue(CtBehavior method)
			throws NotFoundException {

		if (method instanceof CtMethod == false) {
			return false;
		}

		CtClass returnType = ((CtMethod) method).getReturnType();
		String returnTypeName = returnType.getName();

		boolean isVoidMethod = "void".equals(returnTypeName);

		boolean methodReturnsValue = isVoidMethod == false;
		return methodReturnsValue;
	}

	/**
	 * Return javaassist source snippet which lists all the parameters and their
	 * values. If available the source names are extracted from the debug
	 * information and used, otherwise just a number is shown.
	 * 
	 * @param method
	 * @return
	 * @throws NotFoundException
	 */
	public static String getSignature(CtBehavior method)
			throws NotFoundException {

		CtClass parameterTypes[] = method.getParameterTypes();

		CodeAttribute codeAttribute = method.getMethodInfo().getCodeAttribute();

		LocalVariableAttribute locals = null;

		if (codeAttribute != null) {
			AttributeInfo attribute;
			attribute = codeAttribute.getAttribute("LocalVariableTable");
			locals = (LocalVariableAttribute) attribute;
		}

		String methodName = method.getName();

		StringBuffer sb = new StringBuffer(methodName + "(\" ");
		for (int i = 0; i < parameterTypes.length; i++) {
			if (i > 0) {
				// add a comma and a space between printed values
				sb.append(" + \", \" ");
			}

			CtClass parameterType = parameterTypes[i];
			boolean isArray = parameterType.isArray();
			CtClass arrayType = parameterType.getComponentType();
			if (isArray) {
				while (arrayType.isArray()) {
					arrayType = arrayType.getComponentType();
				}
			}

			sb.append(" + \"");
			try {
				sb.append(parameterNameFor(method, locals, i));
			} catch (Exception e) {
				sb.append("" + (i + 1));
			}
			sb.append("\" + \"=");

			if (parameterType.isPrimitive()) {
				// let the compiler handle primitive -> string
				sb.append("\"+ $" + (i + 1));
			} else {
				String s = "org.slf4j.instrumentation.ToStringHelper.render";
				sb.append("\"+ " + s + "($" + (i + 1) + ")");
			}
		}
		sb.append("+\")");

		String signature = sb.toString();
		return signature;
	}

	/**
	 * Determine the name of parameter with index i in the given method. Use the
	 * locals attributes about local variables from the classfile. Note: This is
	 * still work in progress.
	 * 
	 * @param method
	 * @param locals
	 * @param i
	 * @return the name of the parameter if available or a number if not.
	 */
	static String parameterNameFor(CtBehavior method,
			LocalVariableAttribute locals, int i) {

		if (locals == null) {
			return Integer.toString(i + 1);
		}

		int modifiers = method.getModifiers();

		int j = i;

		if (Modifier.isSynchronized(modifiers)) {
			// skip object to synchronize upon.
			j++;
			// System.err.println("Synchronized");
		}
		if (Modifier.isStatic(modifiers) == false) {
			// skip "this"
			j++;
			// System.err.println("Instance");
		}
		String variableName = locals.variableName(j);
		// if (variableName.equals("this")) {
		// System.err.println("'this' returned as a parameter name for "
		// + method.getName() + " index " + j
		// +
		// ", names are probably shifted. Please submit source for class in slf4j bugreport");
		// }
		return variableName;
	}
}