serialversionuidadder.java

asm的源码包 并且包含英文的文档

     */
    public FieldVisitor visitField(
        final int access,
        final String name,
        final String desc,
        final String signature,
        final Object value)
    {
        if (computeSVUID) {
            if (name.equals("serialVersionUID")) {
                // since the class already has SVUID, we won't be computing it.
                computeSVUID = false;
                hasSVUID = true;
            }
            /*
             * Remember field for SVUID computation For field modifiers, only
             * the ACC_PUBLIC, ACC_PRIVATE, ACC_PROTECTED, ACC_STATIC,
             * ACC_FINAL, ACC_VOLATILE, and ACC_TRANSIENT flags are used when
             * computing serialVersionUID values.
             */
            int mods = access
                    & (Opcodes.ACC_PUBLIC | Opcodes.ACC_PRIVATE
                            | Opcodes.ACC_PROTECTED | Opcodes.ACC_STATIC
                            | Opcodes.ACC_FINAL | Opcodes.ACC_VOLATILE | Opcodes.ACC_TRANSIENT);

            if ((access & Opcodes.ACC_PRIVATE) == 0
                    || (access & (Opcodes.ACC_STATIC | Opcodes.ACC_TRANSIENT)) == 0)
            {
                svuidFields.add(new Item(name, mods, desc));
            }
        }

        return super.visitField(access, name, desc, signature, value);
    }

    /*
     * Add the SVUID if class doesn't have one
     */
    public void visitEnd() {
        // compute SVUID and add it to the class
        if (computeSVUID && !hasSVUID) {
            try {
                cv.visitField(Opcodes.ACC_FINAL + Opcodes.ACC_STATIC,
                        "serialVersionUID",
                        "J",
                        null,
                        new Long(computeSVUID()));
            } catch (Throwable e) {
                throw new RuntimeException("Error while computing SVUID for "
                        + name, e);
            }
        }

        super.visitEnd();
    }

    // ------------------------------------------------------------------------
    // Utility methods
    // ------------------------------------------------------------------------

    /**
     * Returns the value of SVUID if the class doesn't have one already. Please
     * note that 0 is returned if the class already has SVUID, thus use
     * <code>isHasSVUID</code> to determine if the class already had an SVUID.
     * 
     * @return Returns the serial version UID
     * @throws IOException
     */
    protected long computeSVUID() throws IOException {
        ByteArrayOutputStream bos = null;
        DataOutputStream dos = null;
        long svuid = 0;

        try {
            bos = new ByteArrayOutputStream();
            dos = new DataOutputStream(bos);

            /*
             * 1. The class name written using UTF encoding.
             */
            dos.writeUTF(name.replace('/', '.'));

            /*
             * 2. The class modifiers written as a 32-bit integer.
             */
            dos.writeInt(access
                    & (Opcodes.ACC_PUBLIC | Opcodes.ACC_FINAL
                            | Opcodes.ACC_INTERFACE | Opcodes.ACC_ABSTRACT));

            /*
             * 3. The name of each interface sorted by name written using UTF
             * encoding.
             */
            Arrays.sort(interfaces);
            for (int i = 0; i < interfaces.length; i++) {
                dos.writeUTF(interfaces[i].replace('/', '.'));
            }

            /*
             * 4. For each field of the class sorted by field name (except
             * private static and private transient fields):
             * 
             * 1. The name of the field in UTF encoding. 2. The modifiers of the
             * field written as a 32-bit integer. 3. The descriptor of the field
             * in UTF encoding
             * 
             * Note that field signatutes are not dot separated. Method and
             * constructor signatures are dot separated. Go figure...
             */
            writeItems(svuidFields, dos, false);

            /*
             * 5. If a class initializer exists, write out the following: 1. The
             * name of the method, <clinit>, in UTF encoding. 2. The modifier of
             * the method, java.lang.reflect.Modifier.STATIC, written as a
             * 32-bit integer. 3. The descriptor of the method, ()V, in UTF
             * encoding.
             */
            if (hasStaticInitializer) {
                dos.writeUTF("<clinit>");
                dos.writeInt(Opcodes.ACC_STATIC);
                dos.writeUTF("()V");
            } // if..

            /*
             * 6. For each non-private constructor sorted by method name and
             * signature: 1. The name of the method, <init>, in UTF encoding. 2.
             * The modifiers of the method written as a 32-bit integer. 3. The
             * descriptor of the method in UTF encoding.
             */
            writeItems(svuidConstructors, dos, true);

            /*
             * 7. For each non-private method sorted by method name and
             * signature: 1. The name of the method in UTF encoding. 2. The
             * modifiers of the method written as a 32-bit integer. 3. The
             * descriptor of the method in UTF encoding.
             */
            writeItems(svuidMethods, dos, true);

            dos.flush();

            /*
             * 8. The SHA-1 algorithm is executed on the stream of bytes
             * produced by DataOutputStream and produces five 32-bit values
             * sha[0..4].
             */
            byte[] hashBytes = computeSHAdigest(bos.toByteArray());

            /*
             * 9. The hash value is assembled from the first and second 32-bit
             * values of the SHA-1 message digest. If the result of the message
             * digest, the five 32-bit words H0 H1 H2 H3 H4, is in an array of
             * five int values named sha, the hash value would be computed as
             * follows:
             * 
             * long hash = ((sha[0] >>> 24) & 0xFF) | ((sha[0] >>> 16) & 0xFF) <<
             * 8 | ((sha[0] >>> 8) & 0xFF) << 16 | ((sha[0] >>> 0) & 0xFF) <<
             * 24 | ((sha[1] >>> 24) & 0xFF) << 32 | ((sha[1] >>> 16) & 0xFF) <<
             * 40 | ((sha[1] >>> 8) & 0xFF) << 48 | ((sha[1] >>> 0) & 0xFF) <<
             * 56;
             */
            for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {
                svuid = (svuid << 8) | (hashBytes[i] & 0xFF);
            }
        } finally {
            // close the stream (if open)
            if (dos != null) {
                dos.close();
            }
        }

        return svuid;
    }

    /**
     * Returns the SHA-1 message digest of the given value.
     * 
     * @param value the value whose SHA message digest must be computed.
     * @return the SHA-1 message digest of the given value.
     */
    protected byte[] computeSHAdigest(final byte[] value) {
        try {
            return MessageDigest.getInstance("SHA").digest(value);
        } catch (Exception e) {
            throw new UnsupportedOperationException(e);
        }
    }

    /**
     * Sorts the items in the collection and writes it to the data output stream
     * 
     * @param itemCollection collection of items
     * @param dos a <code>DataOutputStream</code> value
     * @param dotted a <code>boolean</code> value
     * @exception IOException if an error occurs
     */
    private void writeItems(
        final Collection itemCollection,
        final DataOutputStream dos,
        final boolean dotted) throws IOException
    {
        int size = itemCollection.size();
        Item items[] = (Item[]) itemCollection.toArray(new Item[size]);
        Arrays.sort(items);
        for (int i = 0; i < size; i++) {
            dos.writeUTF(items[i].name);
            dos.writeInt(items[i].access);
            dos.writeUTF(dotted
                    ? items[i].desc.replace('/', '.')
                    : items[i].desc);
        }
    }

    // ------------------------------------------------------------------------
    // Inner classes
    // ------------------------------------------------------------------------

    static class Item implements Comparable {

        String name;

        int access;

        String desc;

        Item(final String name, final int access, final String desc) {
            this.name = name;
            this.access = access;
            this.desc = desc;
        }

        public int compareTo(final Object o) {
            Item other = (Item) o;
            int retVal = name.compareTo(other.name);
            if (retVal == 0) {
                retVal = desc.compareTo(other.desc);
            }
            return retVal;
        }
    }
}