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Java Object Serialization. You thought serialized data was safe? Think again. Ted Neward.
Published on April 0. Updated: April 2. Learn more. Connect more. The new developer. Works Premium membership program provides an. Java developers).
Safari Books Online, deep discounts on premier developer. O'Reilly conferences, and more. Sign up today. A few years ago, while working with a software team writing an application. Java language, I experienced the benefit of knowing a little more. Java Object Serialization.
A year or so prior, a developer responsible for managing the application's. Hashtable. then serialize the Hashtable down to disk for persistence.
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Short of running some kind of data conversion. Hashtable would be the application's storage. About this series. So you think you know about Java programming? The fact is, most.
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Java platform, learning just. In this series, Ted Neward digs beneath the core functionality of the.
Java platform to uncover little known facts that could help you solve. The team felt stuck, but only because they didn't know something crucial. Java Serialization: it was built to allow for. Once I showed them how to do automatic. Hash. Map. proceeded as planned. This article is the first in a series dedicated to uncovering useful trivia.
Java platform — obscure stuff that comes in handy for. Java programming challenges. Java Object Serialization is a great API to start with because it's been. JDK 1. 1. The five things you'll learn about.
Serialization in this article should convince you to look twice at even. Java APIs. Java Serialization 1. Java Object Serialization, introduced as part of the ground- breaking. JDK 1. 1, serves as a mechanism to transform a. Java objects into an array of bytes for storage or transmission. Java objects. In essence, the idea of Serialization is to .
All this happens more. Object. Input. Stream/Object. Output. Stream classes. Serializable. Personpackage com. Person. implements java. Serializable. . Deserializing.
Personpublic class Ser. Test. . We'll use Person. Java Object Serialization. Serialization allows for. Serialization permits a certain amount of class variation, such that even. Object. Input. Stream will still read it just.
The critical things that the Java Object Serialization. Adding new fields to a class. Changing the fields from static to nonstatic. Changing the fields from transient to nontransient. Going the other way (from nonstatic to static or nontransient to transient). Refactoring a serialized. Knowing that Serialization allows for refactoring, let's see what happens.
Person class. Person. V2, shown in Listing 3, introduces a field for gender to. Person class. Listing 3.
Adding a new field to. Personenum Gender.
What we need. therefore, is the serial. Version. UID field, which is calculated. JDK serialver command against the original (or. V1) version of the Person class. Once we have Person's serial. Version. UID, not only.
Person. V2 objects out of the original object's. Serialization is not. It often comes as an unpleasant surprise to Java developers that the.
Serialization binary format is fully documented and entirely reversible. When. making remote method calls via RMI, for example, any private fields in the. Fortunately, Serialization gives us the ability to . We can do this by providing a. Object method on a Serializable object. Obscuring serialized data. Suppose the sensitive data in the Person class were the age.
We can obscure this data by rotating the bits once to the left. It's important to get the details right on both of.
Listing 4, the code will silently fail, and. Person's age will be visible to anyone who looks. Listing 4. Obscuring serialized. Person. implements java. Serializable. ? And, because the format is fully documented.
Serialized data can be signed and. The previous tip assumes that you want to obscure serialized data, not. Although cryptographic. Object and read. Object, there's a better. If you need to encrypt and sign an entire object, the simplest thing is to. Sealed. Object and/or. Signed. Object wrapper.
Both are serializable, so. Sealed. Object creates a sort of . You need a symmetric key to do the. Likewise, you can. Signed. Object for data verification, and again the.
Together, these two objects let you seal and sign serialized data without. Serialization can put a proxy in. From time to time, a class contains a core element of data from which the. In those cases. serializing the entirety of the object is unnecessary.
You could mark the. Given the principal concern is serialization, it's better to nominate a.
Providing a. write. Replace method on the original Person. Resolve method is found during.
Packing and unpacking the. Together, the write. Replace and read.
Resolve. methods enable a Person class to pack a. Person. Proxy with all of its data (or some core subset of it). Listing 5. You complete me, I. Person. Proxy. implements java. Serializable. . Often this means the proxy will need to be an. Person to have access to private fields. The. Proxy will also sometimes need to track down other object references and.
Person's spouse. This trick is one of the few that isn't required to be read/write balanced. Similarly, it could. Replace method to take old classes and. Trust, but validate. It would be nice to assume that the data in the serialized stream is always.
But, as a former. President of the United States once pointed out, it's a safer policy to.
If something looks amiss when it is. Invalid. Object. Exception. In conclusion. Java Object Serialization is more flexible than most Java developers. Fortunately, coding gems like these are scattered all across the JVM. It's. just a matter of knowing about them, and keeping them handy for when a. Next up in the series: Java Collections.
Until then, have fun twisting. Serialization to your evil will! Downloadable resources. Subscribe me to comment notifications.