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package com.sun.xml.internal.bind.v2.bytecode;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.sun.xml.internal.bind.Util;
Replaces a few constant pool tokens from a class "template" and then loads it into the VM.
Author: Kohsuke Kawaguchi
/**
* Replaces a few constant pool tokens from a class "template" and then loads it into the VM.
*
* @author Kohsuke Kawaguchi
*/
public final class ClassTailor {
private ClassTailor() {} // no instanciation please
private static final Logger logger = Util.getClassLogger();
Returns the class name in the JVM format (such as "java/lang/String")
/**
* Returns the class name in the JVM format (such as "java/lang/String")
*/
public static String toVMClassName( Class c ) {
assert !c.isPrimitive();
if(c.isArray())
// I have no idea why it is designed like this, but javap says so.
return toVMTypeName(c);
return c.getName().replace('.','/');
}
public static String toVMTypeName( Class c ) {
if(c.isArray()) {
// TODO: study how an array type is encoded.
return '['+toVMTypeName(c.getComponentType());
}
if(c.isPrimitive()) {
if(c==Boolean.TYPE) return "Z";
if(c==Character.TYPE) return "C";
if(c==Byte.TYPE) return "B";
if(c==Double.TYPE) return "D";
if(c==Float.TYPE) return "F";
if(c==Integer.TYPE) return "I";
if(c==Long.TYPE) return "J";
if(c==Short.TYPE) return "S";
throw new IllegalArgumentException(c.getName());
}
return 'L'+c.getName().replace('.','/')+';';
}
public static byte[] tailor( Class templateClass, String newClassName, String... replacements ) {
String vmname = toVMClassName(templateClass);
return tailor(
SecureLoader.getClassClassLoader(templateClass).getResourceAsStream(vmname+".class"),
vmname, newClassName, replacements );
}
Customizes a class file by replacing constant pools.
Params: - image –
The image of the template class.
- replacements – A list of pair of strings that specify the substitution
String[]{search_0, replace_0, search_1, replace_1, ..., search_n, replace_n } The search strings found in the constant pool will be replaced by the corresponding replacement string.
/**
* Customizes a class file by replacing constant pools.
*
* @param image
* The image of the template class.
* @param replacements
* A list of pair of strings that specify the substitution
* {@code String[]{search_0, replace_0, search_1, replace_1, ..., search_n, replace_n }}
*
* The search strings found in the constant pool will be replaced by the corresponding
* replacement string.
*/
public static byte[] tailor( InputStream image, String templateClassName, String newClassName, String... replacements ) {
DataInputStream in = new DataInputStream(image);
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream(1024);
DataOutputStream out = new DataOutputStream(baos);
// skip until the constant pool count
long l = in.readLong();
out.writeLong(l);
// read the constant pool size
short count = in.readShort();
out.writeShort(count);
// replace constant pools
for( int i=0; i<count; i++ ) {
byte tag = in.readByte();
out.writeByte(tag);
switch(tag) {
case 0:
// this isn't described in the spec,
// but class files often seem to have this '0' tag.
// we can apparently just ignore it, but not sure
// what this really means.
break;
case 1: // CONSTANT_UTF8
{
String value = in.readUTF();
if(value.equals(templateClassName))
value = newClassName;
else {
for( int j=0; j<replacements.length; j+=2 )
if(value.equals(replacements[j])) {
value = replacements[j+1];
break;
}
}
out.writeUTF(value);
}
break;
case 3: // CONSTANT_Integer
case 4: // CONSTANT_Float
out.writeInt(in.readInt());
break;
case 5: // CONSTANT_Long
case 6: // CONSTANT_Double
i++; // doubles and longs take two entries
out.writeLong(in.readLong());
break;
case 7: // CONSTANT_Class
case 8: // CONSTANT_String
out.writeShort(in.readShort());
break;
case 9: // CONSTANT_Fieldref
case 10: // CONSTANT_Methodref
case 11: // CONSTANT_InterfaceMethodref
case 12: // CONSTANT_NameAndType
out.writeInt(in.readInt());
break;
default:
throw new IllegalArgumentException("Unknown constant type "+tag);
}
}
// then copy the rest
byte[] buf = new byte[512];
int len;
while((len=in.read(buf))>0)
out.write(buf,0,len);
in.close();
out.close();
// by now we got the properly tailored class file image
return baos.toByteArray();
} catch( IOException e ) {
// never happen
logger.log(Level.WARNING,"failed to tailor",e);
return null;
}
}
}