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Old JAXB Runtime module. Contains sources required for runtime processing.
There is a newer version: 4.0.5
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package com.sun.xml.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.bind.Util;

/**
 * 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")
     */
    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.
     *
     * @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; i0)
                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;
        }
    }
}