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ClassDump.java
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ClassDump.java
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import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
public class ClassDump {
private Map<Integer, String> constantPoolValues;
ClassDump() {
this.constantPoolValues = new HashMap<Integer, String>();
}
private void dumpClassFile(InputStream input) throws IOException {
byte[] magicWordBytes = readBytes(input, 4);
if (!Arrays.equals(
magicWordBytes,
new byte[] { (byte) 0xCA, (byte) 0xFE, (byte) 0xBA, (byte) 0xBE }
)) {
System.out.println("Not a Java class file.");
return;
}
printBytesWithComment(magicWordBytes, bytesToHexString(magicWordBytes), "Magic number: ", -1);
System.out.println();
byte[] minorVersionBytes = readBytes(input, 2);
int minorVersion = twoBytesToUnsignedInt(minorVersionBytes);
printBytesWithComment(minorVersionBytes, String.format("%d", minorVersion), "Minor version: ", -1);
System.out.println();
byte[] majorVersionBytes = readBytes(input, 2);
int majorVersion = twoBytesToUnsignedInt(majorVersionBytes);
printBytesWithComment(majorVersionBytes, String.format("%d", majorVersion), "Major version: ", -1);
System.out.println();
byte[] constantPoolCountBytes = readBytes(input, 2);
int constantPoolCount = twoBytesToUnsignedInt(constantPoolCountBytes);
printBytesWithComment(constantPoolCountBytes, String.format("%d", constantPoolCount), "Constant pool count + 1: ", -1);
System.out.println();
System.out.println("==CONSTANT POOL==");
for (int i = 1; i < constantPoolCount;) {
i = i + printConstantPoolEntry(i, input);
System.out.println();
}
System.out.println("==END CONSTANT POOL==");
System.out.println();
byte[] accessFlagsBytes = readBytes(input, 2);
int accessFlags = twoBytesToUnsignedInt(accessFlagsBytes);
printBytesWithComment(accessFlagsBytes, String.format("0x%04x", accessFlags), "Access Flags: ", -1);
System.out.println();
byte[] thisClassIndexBytes = readBytes(input, 2);
int thisClassIndex = twoBytesToUnsignedInt(thisClassIndexBytes);
printBytesWithComment(thisClassIndexBytes, String.format("%d", thisClassIndex), "This Class @ #", -1);
System.out.println();
byte[] superClassIndexBytes = readBytes(input, 2);
int superClassIndex = twoBytesToUnsignedInt(superClassIndexBytes);
printBytesWithComment(superClassIndexBytes, String.format("%d", superClassIndex), "Super Class @ #", -1);
System.out.println();
System.out.println("==INTERFACES==");
byte[] interfacesCountBytes = readBytes(input, 2);
int interfacesCount = twoBytesToUnsignedInt(interfacesCountBytes);
printBytesWithComment(interfacesCountBytes, String.format("%d", interfacesCount), "Interfaces count: ", -1);
System.out.println();
if (interfacesCount > 0) {
for (int i = 0; i < interfacesCount; i++) {
byte[] interfaceIndexBytes = readBytes(input, 2);
int interfaceIndex = twoBytesToUnsignedInt(interfaceIndexBytes);
printBytesWithComment(interfaceIndexBytes, String.format("%d", interfaceIndex), "Interface @ #", interfaceIndex);
System.out.println();
}
}
System.out.println("==END INTERFACES==");
System.out.println();
System.out.println("==FIELDS==");
byte[] fieldsCountBytes = readBytes(input, 2);
int fieldsCount = twoBytesToUnsignedInt(fieldsCountBytes);
printBytesWithComment(fieldsCountBytes, String.format("%d", fieldsCount), "Fields count: ", -1);
System.out.println();
if (fieldsCount > 0) {
for (int i = 0; i < fieldsCount; i++) {
printFieldOrMethod(input, "Field");
}
System.out.println();
}
System.out.println("==END FIELDS==");
System.out.println();
System.out.println("==METHODS==");
byte[] methodsCountBytes = readBytes(input, 2);
int methodsCount = twoBytesToUnsignedInt(methodsCountBytes);
printBytesWithComment(methodsCountBytes, String.format("%d", methodsCount), "Methods count: ", -1);
System.out.println();
if (methodsCount > 0) {
for (int i = 0; i < methodsCount; i++) {
printFieldOrMethod(input, "Method");
}
System.out.println();
}
System.out.println("==END METHODS==");
System.out.println();
System.out.println("==ATTRIBUTES==");
byte[] attributesCountBytes = readBytes(input, 2);
int attributesCount = twoBytesToUnsignedInt(attributesCountBytes);
printBytesWithComment(attributesCountBytes, String.format("%d", attributesCount), "Attributes count: ", -1);
System.out.println();
System.out.println("Attributes:");
for (int i = 0; i < attributesCount; i++) {
printAttribute(input);
}
System.out.println("==END ATTRIBUTES==");
System.out.println();
}
private void printFieldOrMethod(InputStream input, String type) throws IOException {
byte[] accessFlagsBytes = readBytes(input, 2);
int accessFlags = twoBytesToUnsignedInt(accessFlagsBytes);
printBytesWithComment(accessFlagsBytes, String.format("0x%04x", accessFlags), "Access flags: ", -1);
byte[] nameIndexBytes = readBytes(input, 2);
int nameIndex = twoBytesToUnsignedInt(nameIndexBytes);
printBytesWithComment(nameIndexBytes, String.format("%d", nameIndex), "Name @ #", nameIndex);
byte[] descriptorIndexBytes = readBytes(input, 2);
int descriptorIndex = twoBytesToUnsignedInt(descriptorIndexBytes);
printBytesWithComment(descriptorIndexBytes, String.format("%d", descriptorIndex), "Descriptor @ #", descriptorIndex);
byte[] attributesCountBytes = readBytes(input, 2);
int attributesCount = twoBytesToUnsignedInt(attributesCountBytes);
printBytesWithComment(attributesCountBytes, String.format("%d", attributesCount), "Attributes count: ", -1);
for (int j = 0; j < attributesCount; j++) {
printAttribute(input);
}
System.out.println();
}
private void printAttribute(InputStream input) throws IOException {
byte[] attributeNameIndexBytes = readBytes(input, 2);
int attributeNameIndex = twoBytesToUnsignedInt(attributeNameIndexBytes);
printBytesWithComment(attributeNameIndexBytes, String.format("%d", attributeNameIndex), "Attribute name @ #", attributeNameIndex);
byte[] attributeLengthBytes = readBytes(input, 4);
long attributeLength = fourBytesToUnsignedLong(attributeLengthBytes);
printBytesWithComment(attributeLengthBytes, String.format("%d", attributeLength), "Attribute length: ", -1);
String attributeName = this.constantPoolValues.get(attributeNameIndex);
decodeAttributeInfo(input, attributeName, attributeLength);
System.out.print("\n"); //end line
}
private void decodeAttributeInfo(InputStream input, String name, long length) throws IOException {
if (!name.equals("Code")) {
System.out.println("// Attribute info:");
for (int i = 0; i < length; i++) {
System.out.printf("%02x ", input.read());
if ((i + 1) % 32 == 0) {
System.out.print("\n"); //end line
}
}
return;
}
//Decode Code attribute
System.out.println("==CODE==");
byte[] maxStackBytes = readBytes(input, 2);
int maxStack = twoBytesToUnsignedInt(maxStackBytes);
printBytesWithComment(maxStackBytes, String.format("%d", maxStack), "Max stack: ", -1);
byte[] maxLocalsBytes = readBytes(input, 2);
int maxLocals = twoBytesToUnsignedInt(maxLocalsBytes);
printBytesWithComment(maxLocalsBytes, String.format("%d", maxLocals), "Max locals: ", -1);
byte[] codeLengthBytes = readBytes(input, 4);
long codeLength = fourBytesToUnsignedLong(codeLengthBytes);
printBytesWithComment(codeLengthBytes, String.format("%d", codeLength), "Code length: ", -1);
System.out.println("// Code bytes:");
for (int i = 0; i < codeLength; i++) {
if (i != 0 && i % 32 == 0) { System.out.print("\n"); }
System.out.printf("%02x ", input.read());
}
System.out.println();
byte[] exceptionTableLengthBytes = readBytes(input, 2);
int exceptionTableLength = twoBytesToUnsignedInt(exceptionTableLengthBytes);
printBytesWithComment(exceptionTableLengthBytes, String.format("%d", exceptionTableLength), "Exception table length: ", -1);
//need code here to handle exceptionTableLength > 0
byte[] attributesCountBytes = readBytes(input, 2);
int attributesCount = twoBytesToUnsignedInt(attributesCountBytes);
printBytesWithComment(attributesCountBytes, String.format("%d", attributesCount), "Attributes count: ", -1);
System.out.println("// Remaining method bytes:");
for (long i = 0; i < length - codeLength - 4 - 2 - 2 - 2 - 2; i++) {
if (i != 0 && i % 32 == 0) { System.out.print("\n"); }
System.out.printf("%02x ", input.read());
}
}
public String intToHexString(int i) {
return String.format("%02x", i);
}
public String byteToHexString(byte b) {
return String.format("%02x", b & 0xFF);
}
public String bytesToHexString(byte[] bytes) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < bytes.length; i++) {
sb.append(byteToHexString(bytes[i]));
if (i < bytes.length - 1) {
sb.append(" ");
}
}
return sb.toString();
}
private void printBytesWithComment(byte[] bytes, String comment, String label, int index) throws IOException {
if (index > 0) {
String value = this.constantPoolValues.get(index);
System.out.println("// " + label + comment + " [\"" + value + "\"]");
} else {
System.out.println("// " + label + comment);
}
System.out.println(bytesToHexString(bytes));
}
private int twoBytesToUnsignedInt(byte[] bytes) throws IOException {
int value = 0;
value |= (bytes[0] & 0xFF) << 8;
value |= bytes[1] & 0xFF;
return value;
}
private long fourBytesToUnsignedLong(byte[] bytes) throws IOException {
return new BigInteger(bytes).longValue();
}
private int constantPoolEntrySize(int tag) {
switch (tag) {
case 1: // Utf8
return 2; // Length of bytes followed by the bytes themselves
case 3: // Integer
case 4: // Float
return 4;
case 5: // Long
case 6: // Double
return 8;
case 7: // Class
case 8: // String
return 2;
case 9: // Fieldref
case 10: // Methodref
case 11: // InterfaceMethodref
case 12: // NameAndType
return 4;
case 15: // MethodHandle
return 3;
case 16: // MethodType
return 2;
case 18: // InvokeDynamic
return 4;
default:
throw new IllegalArgumentException("Invalid constant pool tag: " + tag);
}
}
private byte[] readBytes(InputStream input, int numBytes) throws IOException {
byte[] buffer = new byte[numBytes];
input.read(buffer);
return buffer;
}
private int printConstantPoolEntry(int entryNum, InputStream input) throws IOException {
int tag = input.read();
switch (tag) {
case 1: { //Utf8
byte[] w = readBytes(input, 2);
int length = twoBytesToUnsignedInt(w);
byte[] bytes = new byte[length];
int bytesRead = input.read(bytes);
String value = new String(bytes);
System.out.println("#" + entryNum + " //Utf8: \"" + value + "\" (" + bytesRead + " bytes)");
System.out.println(intToHexString(tag) + ": " + bytesToHexString(bytes));
this.constantPoolValues.put(entryNum, value);
return 1;
}
case 3: { //Integer
byte[] dw = readBytes(input, 4);
long value = fourBytesToUnsignedLong(dw);
System.out.println("#" + entryNum + " //Integer: " + value);
System.out.println(intToHexString(tag) + ": " + bytesToHexString(dw));
return 1;
}
case 4: { //Float
byte[] dw = readBytes(input, 4);
long value = fourBytesToUnsignedLong(dw);
System.out.println("#" + entryNum + " //Float: " + Float.intBitsToFloat((int) value));
System.out.println(intToHexString(tag) + ": " + bytesToHexString(dw));
return 1;
}
case 5: { //Long
byte[] dw1 = readBytes(input, 4);
byte[] dw2 = readBytes(input, 4);
long value = (fourBytesToUnsignedLong(dw1) << 32) | (fourBytesToUnsignedLong(dw2) & 0xFFFFFFFFL);
System.out.println("#" + entryNum + " //Long: " + value);
System.out.println(intToHexString(tag) + ": " + bytesToHexString(dw1) + ", " + bytesToHexString(dw2));
return 2;
}
case 6: { //Double
byte[] dw1 = readBytes(input, 4);
byte[] dw2 = readBytes(input, 4);
long value = (fourBytesToUnsignedLong(dw1) << 32) | (fourBytesToUnsignedLong(dw2) & 0xFFFFFFFFL);
System.out.println("#" + entryNum + " //Double: " + Double.longBitsToDouble(value));
System.out.println(intToHexString(tag) + ": " + bytesToHexString(dw1) + ", " + bytesToHexString(dw2));
return 2;
}
case 7: { //Class: Name (index)
byte[] w = readBytes(input, 2);
int index = twoBytesToUnsignedInt(w);
System.out.println("#" + entryNum + " //Class: Name @ #" + index + " [Utf8]");
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w));
return 1;
}
case 8: { //String (index)
byte[] w = readBytes(input, 2);
int index = twoBytesToUnsignedInt(w);
System.out.println("#" + entryNum + " //String @ #" + index + " [Utf8]");
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w));
return 1;
}
case 9: { //Fieldref: Class (index), NameAndType (index)
byte[] w1 = readBytes(input, 2);
byte[] w2 = readBytes(input, 2);
int classIndex = twoBytesToUnsignedInt(w1);
int nameAndTypeIndex = twoBytesToUnsignedInt(w2);
System.out.println("#" + entryNum + " //Fieldref: Class @ #" + classIndex + ", NameAndType @ #" + nameAndTypeIndex);
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w1) + ", " + bytesToHexString(w2));
return 1;
}
case 10: { //Methodref: Class (index), NameAndType (index)
byte[] w1 = readBytes(input, 2);
byte[] w2 = readBytes(input, 2);
int classIndex = twoBytesToUnsignedInt(w1);
int nameAndTypeIndex = twoBytesToUnsignedInt(w2);
System.out.println("#" + entryNum + " //Methodref: Class @ #" + classIndex + ", NameAndType @ #" + nameAndTypeIndex);
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w1) + ", " + bytesToHexString(w2));
return 1;
}
case 11: { //InterfaceMethodref: Class (index), NameAndType (index)
byte[] w1 = readBytes(input, 2);
byte[] w2 = readBytes(input, 2);
int classIndex = twoBytesToUnsignedInt(w1);
int nameAndTypeIndex = twoBytesToUnsignedInt(w2);
System.out.println("#" + entryNum + " //InterfaceMethodref: Class @ #" + classIndex + ", NameAndType @ #" + nameAndTypeIndex);
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w1) + ", " + bytesToHexString(w2));
return 1;
}
case 12: { //NameAndType: Name (index), Descriptor (index)
byte[] w1 = readBytes(input, 2);
byte[] w2 = readBytes(input, 2);
int nameIndex = twoBytesToUnsignedInt(w1);
int descriptorIndex = twoBytesToUnsignedInt(w2);
System.out.println("#" + entryNum + " //NameAndType: Name @ #" + nameIndex + " [Utf8], Type Descriptor @ #" + descriptorIndex + " [Utf8]");
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w1) + ", " + bytesToHexString(w2));
return 1;
}
case 15: { //MethodHandle: ReferenceKind, Reference (index)
int i = input.read();
byte[] w = readBytes(input, 2);
int referenceIndex = twoBytesToUnsignedInt(w);
System.out.println("#" + entryNum + " //MethodHandle: ReferenceKind " + i + ", Reference @ #" + referenceIndex);
System.out.println(intToHexString(tag) + ": " + intToHexString(i) + ", " + bytesToHexString(w));
return 1;
}
case 16: { //MethodType: Descriptor (index)
byte[] w = readBytes(input, 2);
int descriptorIndex = twoBytesToUnsignedInt(w);
System.out.println("#" + entryNum + " //MethodType: Type Descriptor @ #" + descriptorIndex + " [Utf8]");
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w));
return 1;
}
case 18: { //InvokeDynamic: BootstrapMethodAttr (index), NameAndType (index)
byte[] w1 = readBytes(input, 2);
byte[] w2 = readBytes(input, 2);
int bootstrapMethodAttrIndex = twoBytesToUnsignedInt(w1);
int nameAndTypeIndex = twoBytesToUnsignedInt(w2);
System.out.println(
"#" + entryNum +
" //InvokeDynamic: BootstrapMethodAttr @ #" + bootstrapMethodAttrIndex +
", NameAndType @ #" + nameAndTypeIndex
);
System.out.println(intToHexString(tag) + ": " + bytesToHexString(w1) + ", " + bytesToHexString(w2));
return 1;
}
default:
throw new IllegalArgumentException("Invalid constant pool tag: " + tag);
}
}
private void dumpEntireHexContents(String classFileName, InputStream input) throws IOException {
System.out.println("Hex Dump of " + classFileName + ":");
ByteArrayOutputStream buffer = new ByteArrayOutputStream();
int nRead;
byte[] data = new byte[16384];
while ((nRead = input.read(data, 0, data.length)) != -1) {
buffer.write(data, 0, nRead);
}
buffer.flush();
byte[] byteArray = buffer.toByteArray();
for (int i = 0; i < byteArray.length; i++) {
System.out.printf("%02x ", byteArray[i]);
if ((i + 1) % 32 == 0) {
System.out.print("\n"); //blank line
}
}
System.out.print("\n"); //end line
System.out.print("\n"); //blank line
}
public static void main(String[] args) throws IOException {
if (args.length != 1) {
System.out.println("Usage: java ClassDump <class file>");
return;
}
String filename = args[0];
ClassDump cd = new ClassDump();
try (InputStream input = new FileInputStream(filename)) {
cd.dumpEntireHexContents(filename, input);
}
// Reopen the input stream to process it again
try (InputStream input = new FileInputStream(filename)) {
cd.dumpClassFile(input);
}
}
}