Class file reader for obtaining the parameter names for declared methods in a class
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
/**
* This is the class file reader for obtaining the parameter names for declared
* methods in a class. The class must have debugging attributes for us to obtain
* this information.
* <p>
* This does not work for inherited methods. To obtain parameter names for
* inherited methods, you must use a paramReader for the class that originally
* declared the method.
* <p>
* don't get tricky, it's the bare minimum. Instances of this class are not
* threadsafe -- don't share them.
* <p>
*
* @author Edwin Smith, Macromedia
*/
public class ClassReader extends ByteArrayInputStream {
// constants values that appear in java class files,
// from jvm spec 2nd ed, section 4.4, pp 103
private static final int CONSTANT_CLASS = 7;
private static final int CONSTANT_FIELDREF = 9;
private static final int CONSTANT_METHODREF = 10;
private static final int CONSTANT_INTERFACE_METHOD_REF = 11;
private static final int CONSTANT_STRING = 8;
private static final int CONSTANT_INTEGER = 3;
private static final int CONSTANT_FLOAT = 4;
private static final int CONSTANT_LONG = 5;
private static final int CONSTANT_DOUBLE = 6;
private static final int CONSTANT_NAME_AND_TYPE = 12;
private static final int CONSTANT_UTF_8 = 1;
/**
* the constant pool. constant pool indices in the class file directly index
* into this array. The value stored in this array is the position in the
* class file where that constant begins.
*/
private int[] cpoolIndex;
private Object[] cpool;
private Map<String, Method> attrMethods;
protected ClassReader(byte buf[], Map<String, Method> attrMethods) {
super(buf);
this.attrMethods = attrMethods;
}
/**
* load the bytecode for a given class, by using the class's defining
* classloader and assuming that for a class named P.C, the bytecodes are in
* a resource named /P/C.class.
*
* @param c the class of interest
* @return a byte array containing the bytecode
* @throws IOException
*/
protected static byte[] getBytes(Class c) throws IOException {
InputStream fin = c.getResourceAsStream('/' + c.getName().replace('.', '/') + ".class");
if (fin == null) {
throw new IOException();
}
try {
ByteArrayOutputStream out = new ByteArrayOutputStream();
byte[] buf = new byte[1024];
int actual;
do {
actual = fin.read(buf);
if (actual > 0) {
out.write(buf, 0, actual);
}
} while (actual > 0);
return out.toByteArray();
} finally {
fin.close();
}
}
static String classDescriptorToName(String desc) {
return desc.replace('/', '.');
}
protected static Map<String, Method> findAttributeReaders(Class c) {
Map<String, Method> map = new HashMap<String, Method>();
Method[] methods = c.getMethods();
for (int i = 0; i < methods.length; i++) {
String name = methods[i].getName();
if (name.startsWith("read") && methods[i].getReturnType() == void.class) {
map.put(name.substring(4), methods[i]);
}
}
return map;
}
protected static String getSignature(Member method, Class[] paramTypes) {
// compute the method descriptor
StringBuffer b = new StringBuffer((method instanceof Method) ? method.getName() : "<init>");
b.append('(');
for (int i = 0; i < paramTypes.length; i++) {
addDescriptor(b, paramTypes[i]);
}
b.append(')');
if (method instanceof Method) {
addDescriptor(b, ((Method)method).getReturnType());
} else if (method instanceof Constructor) {
addDescriptor(b, void.class);
}
return b.toString();
}
private static void addDescriptor(StringBuffer b, Class c) {
if (c.isPrimitive()) {
if (c == void.class) {
b.append('V');
} else if (c == int.class) {
b.append('I');
} else if (c == boolean.class) {
b.append('Z');
} else if (c == byte.class) {
b.append('B');
} else if (c == short.class) {
b.append('S');
} else if (c == long.class) {
b.append('J');
} else if (c == char.class) {
b.append('C');
} else if (c == float.class) {
b.append('F');
} else if (c == double.class) {
b.append('D');
}
} else if (c.isArray()) {
b.append('[');
addDescriptor(b, c.getComponentType());
} else {
b.append('L').append(c.getName().replace('.', '/')).append(';');
}
}
/**
* @return the next unsigned 16 bit value
*/
protected final int readShort() {
return (read() << 8) | read();
}
/**
* @return the next signed 32 bit value
*/
protected final int readInt() {
return (read() << 24) | (read() << 16) | (read() << 8) | read();
}
/**
* skip n bytes in the input stream.
*/
protected void skipFully(int n) throws IOException {
while (n > 0) {
int c = (int)skip(n);
if (c <= 0) {
throw new EOFException();
}
n -= c;
}
}
protected final Member resolveMethod(int index) throws IOException, ClassNotFoundException,
NoSuchMethodException {
int oldPos = pos;
try {
Member m = (Member)cpool[index];
if (m == null) {
pos = cpoolIndex[index];
Class owner = resolveClass(readShort());
NameAndType nt = resolveNameAndType(readShort());
String signature = nt.name + nt.type;
if ("<init>".equals(nt.name)) {
Constructor[] ctors = owner.getConstructors();
for (int i = 0; i < ctors.length; i++) {
String sig = getSignature(ctors[i], ctors[i].getParameterTypes());
if (sig.equals(signature)) {
cpool[index] = ctors[i];
m = ctors[i];
return m;
}
}
} else {
Method[] methods = owner.getDeclaredMethods();
for (int i = 0; i < methods.length; i++) {
String sig = getSignature(methods[i], methods[i].getParameterTypes());
if (sig.equals(signature)) {
cpool[index] = methods[i];
m = methods[i];
return m;
}
}
}
throw new NoSuchMethodException(signature);
}
return m;
} finally {
pos = oldPos;
}
}
protected final Field resolveField(int i) throws IOException, ClassNotFoundException,
NoSuchFieldException {
int oldPos = pos;
try {
Field f = (Field)cpool[i];
if (f == null) {
pos = cpoolIndex[i];
Class owner = resolveClass(readShort());
NameAndType nt = resolveNameAndType(readShort());
cpool[i] = owner.getDeclaredField(nt.name);
f = owner.getDeclaredField(nt.name);
}
return f;
} finally {
pos = oldPos;
}
}
protected final NameAndType resolveNameAndType(int i) throws IOException {
int oldPos = pos;
try {
NameAndType nt = (NameAndType)cpool[i];
if (nt == null) {
pos = cpoolIndex[i];
String name = resolveUtf8(readShort());
String type = resolveUtf8(readShort());
cpool[i] = new NameAndType(name, type);
nt = new NameAndType(name, type);
}
return nt;
} finally {
pos = oldPos;
}
}
protected final Class resolveClass(int i) throws IOException, ClassNotFoundException {
int oldPos = pos;
try {
Class c = (Class)cpool[i];
if (c == null) {
pos = cpoolIndex[i];
String name = resolveUtf8(readShort());
cpool[i] = Class.forName(classDescriptorToName(name));
c = Class.forName(classDescriptorToName(name));
}
return c;
} finally {
pos = oldPos;
}
}
protected final String resolveUtf8(int i) throws IOException {
int oldPos = pos;
try {
String s = (String)cpool[i];
if (s == null) {
pos = cpoolIndex[i];
int len = readShort();
skipFully(len);
cpool[i] = new String(buf, pos - len, len, "utf-8");
s = new String(buf, pos - len, len, "utf-8");
}
return s;
} finally {
pos = oldPos;
}
}
@SuppressWarnings("fallthrough")
protected final void readCpool() throws IOException {
int count = readShort(); // cpool count
cpoolIndex = new int[count];
cpool = new Object[count];
for (int i = 1; i < count; i++) {
int c = read();
cpoolIndex[i] = super.pos;
// constant pool tag
switch (c) {
case CONSTANT_FIELDREF:
case CONSTANT_METHODREF:
case CONSTANT_INTERFACE_METHOD_REF:
case CONSTANT_NAME_AND_TYPE:
readShort(); // class index or (12) name index
// fall through
case CONSTANT_CLASS:
case CONSTANT_STRING:
readShort(); // string index or class index
break;
case CONSTANT_LONG:
case CONSTANT_DOUBLE:
readInt(); // hi-value
// see jvm spec section 4.4.5 - double and long cpool
// entries occupy two "slots" in the cpool table.
i++;
// fall through
case CONSTANT_INTEGER:
case CONSTANT_FLOAT:
readInt(); // value
break;
case CONSTANT_UTF_8:
int len = readShort();
skipFully(len);
break;
default:
// corrupt class file
throw new IllegalStateException();
}
}
}
protected final void skipAttributes() throws IOException {
int count = readShort();
for (int i = 0; i < count; i++) {
readShort(); // name index
skipFully(readInt());
}
}
/**
* read an attributes array. the elements of a class file that can contain
* attributes are: fields, methods, the class itself, and some other types
* of attributes.
*/
protected final void readAttributes() throws IOException {
int count = readShort();
for (int i = 0; i < count; i++) {
int nameIndex = readShort(); // name index
int attrLen = readInt();
int curPos = pos;
String attrName = resolveUtf8(nameIndex);
Method m = attrMethods.get(attrName);
if (m != null) {
try {
m.invoke(this, new Object[] {});
} catch (IllegalAccessException e) {
pos = curPos;
skipFully(attrLen);
} catch (InvocationTargetException e) {
try {
throw e.getTargetException();
} catch (Error ex) {
throw ex;
} catch (RuntimeException ex) {
throw ex;
} catch (IOException ex) {
throw ex;
} catch (Throwable ex) {
pos = curPos;
skipFully(attrLen);
}
}
} else {
// don't care what attribute this is
skipFully(attrLen);
}
}
}
/**
* read a code attribute
*
* @throws IOException
*/
public void readCode() throws IOException {
readShort(); // max stack
readShort(); // max locals
skipFully(readInt()); // code
skipFully(8 * readShort()); // exception table
// read the code attributes (recursive). This is where
// we will find the LocalVariableTable attribute.
readAttributes();
}
private static class NameAndType {
String name;
String type;
public NameAndType(String name, String type) {
this.name = name;
this.type = type;
}
}
}
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