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Prettypb serialization runtime
There is a newer version: 0.3.5
package net.dongliu.prettypb.runtime.code;

import net.dongliu.prettypb.runtime.include.ProtoType;
import net.dongliu.prettypb.runtime.utils.Constant;

import java.io.Closeable;
import java.io.IOException;
import java.io.OutputStream;

/**
 * write protobuf fields
 *
 * @author Dong Liu
 */
public class ProtoBufWriter implements Closeable {
    private final OutputStream os;

    public ProtoBufWriter(OutputStream os) {
        this.os = os;
    }


    /**
     * write Little-Endian base128 VarInt
     *
     * @param num
     */
    public void writeVarInt(int num) throws IOException {
        for (int i = 0; i < 5; i++) {
            byte b = (byte) (num & 0x7f);
            num = num >> 7;
            if (num != 0) {
                os.write((b | 0x80));
            } else {
                os.write(b);
                break;
            }
        }
    }


    /**
     * write Little-Endian base128 VarInt
     *
     * @param num
     */
    public void writeVarLong(long num) throws IOException {
        for (int i = 0; i < 10; i++) {
            byte b = (byte) (num & 0x7f);
            num = num >> 7;
            if (num != 0) {
                os.write((byte) (b | 0x80));
            } else {
                os.write(b);
                break;
            }
        }
    }

    /**
     * for protobuf sint32 type
     *
     * @param num
     */
    public void writeVarSInt(int num) throws IOException {
        writeVarInt(zigzag(num));
    }

    /**
     * for protobuf sint64 type
     *
     * @param num
     */
    public void writeVarSLong(long num) throws IOException {
        writeVarLong(zigzag(num));
    }

    protected static int zigzag(int num) {
        return (num << 1) ^ (num >> 31);
    }

    protected static long zigzag(long num) {
        return (num << 1) ^ (num >> 63);
    }

    public void writeFixedInt(int num) throws IOException {
        os.write((num & 0xff));
        os.write(((num >> 8) & 0xff));
        os.write(((num >> 16) & 0xff));
        os.write(((num >> 24) & 0xff));
    }

    public void writeFloat(float num) throws IOException {
        int i = Float.floatToRawIntBits(num);
        writeFixedInt(i);
    }

    public void writeDouble(double num) throws IOException {
        long l = Double.doubleToRawLongBits(num);
        writeFixedLong(l);
    }

    public void writeFixedLong(long num) throws IOException {
        os.write((int) (num & 0xff));
        os.write((int) ((num >> 8) & 0xff));
        os.write((int) ((num >> 16) & 0xff));
        os.write((int) ((num >> 24) & 0xff));
        os.write((int) ((num >> 32) & 0xff));
        os.write((int) ((num >> 40) & 0xff));
        os.write((int) ((num >> 48) & 0xff));
        os.write((int) ((num >> 56) & 0xff));
    }

    public void writeString(String str) throws IOException {
        byte[] bytes = str.getBytes(Constant.charset);
        writeVarInt(bytes.length);
        os.write(bytes);
    }

    public void writeBytes(byte[] bytes) throws IOException {
        writeVarInt(bytes.length);
        os.write(bytes);
    }

    public void writeByte(byte b) throws IOException {
        os.write(b);
    }

    public void encodeTag(int wireType, int idx) throws IOException {
        int i = idx << 3 | wireType;
        writeVarInt(i);
    }

    public void encodeTag(ProtoType protoType, int idx) throws IOException {
        encodeTag(protoType.getWireType(), idx);
    }

    @Override
    public void close() throws IOException {
        this.os.close();
    }
}