The goal of protostuff is to generate a schema whether at compile-time or runtime and use that for reading/writing to various formats via the provided IO libs.

Schema

A class that encapsulates:

• the serialization logic of an object
• the deserialization logic of an object
• the validation of an object’s required fields
• the mapping of an object’s field names to field numbers
• the instantiation of the object.

For existing objects, use protostuff-runtime which uses reflection.

If you prefer to manually write the schema (to validate some fields), take a look at the example pojo below and it's corresponding schema.

User.java

public final class User
{
    String firstName;
    String lastName;
    String email;
    List<User> friends;

    public User() {}

    public User(String email)
    {
        this.email = email;
    }

    // getters and setters
}

This is how your hand-written schema would look like:

UserSchema.java

public class UserSchema implements Schema<User>
{
    public boolean isInitialized(User user)
    {
        return user.getEmail() != null;
    }

    public void mergeFrom(Input input, User user) throws IOException
    {
        while (true)
        {
            int number = input.readFieldNumber(this);
            switch(number)
            {
                case 0:
                    return;
                case 1:
                    user.setEmail(input.readString());
                    break;
                case 2:
                    user.setFirstName(input.readString());
                    break;
                case 3:
                    user.setLastName(input.readString());
                    break;
                case 4:
                    if (message.friends == null)
                        message.friends = new ArrayList<User>();
                    message.friends.add(input.mergeObject(null, this));
                    break;
                default:
                    input.handleUnknownField(number, this);
            }
        }
    }

    public void writeTo(Output output, User user) throws IOException
    {
        if (user.getEmail() == null)
            throw new UninitializedMessageException(user, this);

        output.writeString(1, user.getEmail(), false);

        if (user.getFirstName() != null)
            output.writeString(2, user.getFirstName(), false);

        if (user.getLastName() != null)
            output.writeString(3, user.getLastName(), false);

        if (message.friends != null)
        {
            for (User friend : message.friends)
            {
                if (friend != null)
                    output.writeObject(4, friend, this, true);
            }
        }
    }

    public User newMessage()
    {
        return new User();
    }

    public Class<User> typeClass()
    {
        return User.class;
    }

    public String messageName()
    {
        return User.class.getSimpleName();
    }

    public String messageFullName()
    {
        return User.class.getName();
    }

    // the mapping between the field names to the field numbers.

    public String getFieldName(int number)
    {
        switch(number)
        {
            case 1:
                return "email";
            case 2:
                return "firstName";
            case 3:
                return "lastName";
            case 4:
                return "friends";
            default:
                return null;
        }
    }

    public int getFieldNumber(String name)
    {
        Integer number = fieldMap.get(name);
        return number == null ? 0 : number.intValue();
    }

    private static final HashMap<String,Integer> fieldMap = new HashMap<String,Integer>();    
    static
    {
        fieldMap.put("email", 1);
        fieldMap.put("firstName", 2);
        fieldMap.put("lastName", 3);
        fieldMap.put("friends", 4);
    }
}