Marshalling (computer science)

To "serialize" an object means to convert its state into a byte stream in such a way that the byte stream can be converted back into a copy of the object.

The term "marshal" is used for a specific type of "serialization" in the Python standard library[2] – storing internal python objects:

The marshal module exists mainly to support reading and writing the “pseudo-compiled” code for Python modules of .pyc files.

…

If you’re serializing and de-serializing Python objects, use the pickle module instead

— The Python Standard Library[3]

In the Java-related RFC 2713, marshalling is used when serialising objects for remote invocation. An object that is marshalled records the state of the original object and it contains the codebase (codebase here refers to a list of URLs where the object code can be loaded from, and not source code). Hence, in order to convert the object state and codebase(s), unmarshalling must be done. The unmarshaller interface automatically converts the marshalled data containing codebase(s) into an executable Java object in JAXB. Any object that can be deserialized can be unmarshalled. However, the converse need not be true.

To "marshal" an object means to record its state and codebase(s) in such a way that when the marshalled object is "unmarshalled," a copy of the original object is obtained, possibly by automatically loading the class definitions of the object. You can marshal any object that is serializable or remote (that is, implements the java.rmi.Remote interface). Marshalling is like serialization, except marshalling also records codebases. Marshalling is different from serialization in that marshalling treats remote objects specially.

…

Any object whose methods can be invoked [on an object in another Java virtual machine] must implement the java.rmi.Remote interface. When such an object is invoked, its arguments are marshalled and sent from the local virtual machine to the remote one, where the arguments are unmarshalled and used.

— Schema for Representing Java(tm) Objects in an LDAP Directory (RFC 2713)[4]

In Microsoft .NET, marshalling is also used to refer to serialization when using remote calls:

When you marshal an object by value, a copy of the object is created and serialized to the server. Any method calls made on that object are done on the server

— How To Marshal an Object to a Remote Server by Value by Using Visual Basic .NET (Q301116)[5]

Marshalling is used within implementations of different remote procedure call (RPC) mechanisms, where it is necessary to transport data between processes and/or between threads. In Microsoft's Component Object Model (COM), interface pointers must be marshalled when crossing COM apartment boundaries.[6][7] In the .NET Framework, the conversion between an unmanaged type and a CLR type, as in the P/Invoke process, is also an example of an action that requires marshalling to take place.[8]

Additionally, marshalling is used extensively within scripts and applications that use the XPCOM technologies provided within the Mozilla application framework. The Mozilla Firefox browser is a popular application built with this framework, that additionally allows scripting languages to use XPCOM through XPConnect (Cross-Platform Connect).

XML is one means of transferring data between systems. Microsoft, for example, uses it as the basis of the file formats of the various components (Word, Excel, Access, PowerPoint, etc.) of the Microsoft Office suite (see Office Open XML). While this typically results in a verbose wire format, XML's fully-bracketed "start-tag", "end-tag" syntax allows provision of more accurate diagnostics and easier recovery from transmission or disk errors. In addition, because the tags occur repeatedly, one can use standard compression methods to shrink the content—all the Office file formats are created by zipping the raw XML.[10] Alternative formats such as JSON (JavaScript Object Notation) are more concise, but correspondingly less robust for error recovery.

Once the data is transferred to a program or an application, it needs to be converted back to an object for usage. Hence, unmarshalling is generally used in the receiver end of the implementations of Remote Method Invocation (RMI) and Remote procedure call (RPC) mechanisms to unmarshal transmitted objects in an executable form.

public class Student
{
    private char name[150];
    private int ID;
    public String getName()
    {
        return this.name;
    }
    public int getID()
    {
        return this.ID;
    }
    void setName(String name)
    {
        this.name = name;
    }
    void setID(int ID)
    {
        this.ID = ID;
    }
}

<!-- Code Snippet 1 -->

<?xml version="1.0" encoding="UTF-8"?>
    <student id="11235813">
        <name>Jayaraman</name>
    </student>
    <student id="21345589">
        <name>Shyam</name>
    </student>

// Code Snippet 2

Student s1 = new Student();
s1.setID(11235813);
s1.setName("Jayaraman");
Student s2 = new Student();
s2.setID(21345589);
s2.setName("Shyam");

Look up marshalling in Wiktionary, the free dictionary.

• Free and open-source graphics device driver#Software architecture
• Component Object Model
• CORBA
• Pickle (Python)
• Protocol Buffers
• Java Architecture for XML Binding