/*
* Copyright 2002-2008 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.core;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.HashMap;
import java.util.Map;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.commons.EmptyVisitor;
import org.springframework.util.ClassUtils;
/**
* Implementation of {@link ParameterNameDiscoverer} that uses the LocalVariableTable
* information in the method attributes to discover parameter names. Returns
* <code>null</code> if the class file was compiled without debug information.
*
* <p>Uses ObjectWeb's ASM library for analyzing class files. Each discoverer
* instance caches the ASM ClassReader for each introspected Class, in a
* thread-safe manner. It is recommended to reuse discoverer instances
* as far as possible.
*
* @author Adrian Colyer
* @author Juergen Hoeller
* @since 2.0
*/
public class LocalVariableTableParameterNameDiscoverer implements ParameterNameDiscoverer {
private static Log logger = LogFactory.getLog(LocalVariableTableParameterNameDiscoverer.class);
private final Map parameterNamesCache = CollectionFactory.createConcurrentMapIfPossible(16);
private final Map classReaderCache = new HashMap();
public String[] getParameterNames(Method method) {
String[] paramNames = (String[]) this.parameterNamesCache.get(method);
if (paramNames == null) {
try {
paramNames = visitMethod(method).getParameterNames();
if (paramNames != null) {
this.parameterNamesCache.put(method, paramNames);
}
}
catch (IOException ex) {
// We couldn't load the class file, which is not fatal as it
// simply means this method of discovering parameter names won't work.
if (logger.isDebugEnabled()) {
logger.debug("IOException whilst attempting to read '.class' file for class [" +
method.getDeclaringClass().getName() +
"] - unable to determine parameter names for method: " + method, ex);
}
}
}
return paramNames;
}
public String[] getParameterNames(Constructor ctor) {
String[] paramNames = (String[]) this.parameterNamesCache.get(ctor);
if (paramNames == null) {
try {
paramNames = visitConstructor(ctor).getParameterNames();
if (paramNames != null) {
this.parameterNamesCache.put(ctor, paramNames);
}
}
catch (IOException ex) {
// We couldn't load the class file, which is not fatal as it
// simply means this method of discovering parameter names won't work.
if (logger.isDebugEnabled()) {
logger.debug("IOException whilst attempting to read '.class' file for class [" +
ctor.getDeclaringClass().getName() +
"] - unable to determine parameter names for constructor: " + ctor, ex);
}
}
}
return paramNames;
}
/**
* Visit the given method and discover its parameter names.
*/
private ParameterNameDiscoveringVisitor visitMethod(Method method) throws IOException {
ClassReader classReader = getClassReader(method.getDeclaringClass());
FindMethodParameterNamesClassVisitor classVisitor = new FindMethodParameterNamesClassVisitor(method);
classReader.accept(classVisitor, false);
return classVisitor;
}
/**
* Visit the given constructor and discover its parameter names.
*/
private ParameterNameDiscoveringVisitor visitConstructor(Constructor ctor) throws IOException {
ClassReader classReader = getClassReader(ctor.getDeclaringClass());
FindConstructorParameterNamesClassVisitor classVisitor = new FindConstructorParameterNamesClassVisitor(ctor);
classReader.accept(classVisitor, false);
return classVisitor;
}
/**
* Obtain a (cached) ClassReader for the given class.
*/
private ClassReader getClassReader(Class clazz) throws IOException {
synchronized (this.classReaderCache) {
ClassReader classReader = (ClassReader) this.classReaderCache.get(clazz);
if (classReader == null) {
InputStream is = clazz.getResourceAsStream(ClassUtils.getClassFileName(clazz));
if (is == null) {
throw new FileNotFoundException("Class file for class [" + clazz.getName() + "] not found");
}
try {
classReader = new ClassReader(is);
this.classReaderCache.put(clazz, classReader);
}
finally {
is.close();
}
}
return classReader;
}
}
/**
* Helper class that looks for a given member name and descriptor, and then
* attempts to find the parameter names for that member.
*/
private static abstract class ParameterNameDiscoveringVisitor extends EmptyVisitor {
private String methodNameToMatch;
private String descriptorToMatch;
private int numParamsExpected;
/*
* The nth entry contains the slot index of the LVT table entry holding the
* argument name for the nth parameter.
*/
private int[] lvtSlotIndex;
private String[] parameterNames;
public ParameterNameDiscoveringVisitor(String name, boolean isStatic, Class[] paramTypes) {
this.methodNameToMatch = name;
this.numParamsExpected = paramTypes.length;
computeLvtSlotIndices(isStatic, paramTypes);
}
public void setDescriptorToMatch(String descriptor) {
this.descriptorToMatch = descriptor;
}
public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
if (name.equals(this.methodNameToMatch) && desc.equals(this.descriptorToMatch)) {
return new LocalVariableTableVisitor(this, isStatic(access));
}
else {
// Not interested in this method...
return null;
}
}
private boolean isStatic(int access) {
return ((access & Opcodes.ACC_STATIC) > 0);
}
public String[] getParameterNames() {
return this.parameterNames;
}
private void computeLvtSlotIndices(boolean isStatic, Class[] paramTypes) {
this.lvtSlotIndex = new int[paramTypes.length];
int nextIndex = (isStatic ? 0 : 1);
for (int i = 0; i < paramTypes.length; i++) {
this.lvtSlotIndex[i] = nextIndex;
if (isWideType(paramTypes[i])) {
nextIndex += 2;
}
else {
nextIndex++;
}
}
}
private boolean isWideType(Class aType) {
return (aType == Long.TYPE || aType == Double.TYPE);
}
}
private static class FindMethodParameterNamesClassVisitor extends ParameterNameDiscoveringVisitor {
public FindMethodParameterNamesClassVisitor(Method method) {
super(method.getName(), Modifier.isStatic(method.getModifiers()), method.getParameterTypes());
setDescriptorToMatch(Type.getMethodDescriptor(method));
}
}
private static class FindConstructorParameterNamesClassVisitor extends ParameterNameDiscoveringVisitor {
public FindConstructorParameterNamesClassVisitor(Constructor ctor) {
super("<init>", false, ctor.getParameterTypes());
Type[] pTypes = new Type[ctor.getParameterTypes().length];
for (int i = 0; i < pTypes.length; i++) {
pTypes[i] = Type.getType(ctor.getParameterTypes()[i]);
}
setDescriptorToMatch(Type.getMethodDescriptor(Type.VOID_TYPE, pTypes));
}
}
private static class LocalVariableTableVisitor extends EmptyVisitor {
private final ParameterNameDiscoveringVisitor memberVisitor;
private final boolean isStatic;
private String[] parameterNames;
private boolean hasLvtInfo = false;
public LocalVariableTableVisitor(ParameterNameDiscoveringVisitor memberVisitor, boolean isStatic) {
this.memberVisitor = memberVisitor;
this.isStatic = isStatic;
this.parameterNames = new String[memberVisitor.numParamsExpected];
}
public void visitLocalVariable(
String name, String description, String signature, Label start, Label end, int index) {
this.hasLvtInfo = true;
int[] lvtSlotIndices = this.memberVisitor.lvtSlotIndex;
for (int i = 0; i < lvtSlotIndices.length; i++) {
if (lvtSlotIndices[i] == index) {
this.parameterNames[i] = name;
}
}
}
public void visitEnd() {
if (this.hasLvtInfo || (this.isStatic && this.parameterNames.length == 0)) {
// visitLocalVariable will never be called for static no args methods
// which doesn't use any local variables.
// This means that hasLvtInfo could be false for that kind of methods
// even if the class has local variable info.
this.memberVisitor.parameterNames = this.parameterNames;
}
}
}
}