Effective Java

---

ITEM 90: CONSIDER SERIALIZATION PROXIES INSTEAD OF SERIALIZED INSTANCES
363
Item 90: Consider serialization proxies instead of serialized 
instances
As mentioned in Items 85 and 86 and discussed throughout this chapter, the deci-
sion to implement 
Serializable
increases the likelihood of bugs and security
problems as it allows instances to be created using an extralinguistic mechanism
in place of ordinary constructors. There is, however, a technique that greatly
reduces these risks. This technique is known as the 
serialization proxy pattern
.
The serialization proxy pattern is reasonably straightforward. First, design a
private static nested class that concisely represents the logical state of an instance
of the enclosing class. This nested class is known as the 
serialization proxy
of the
enclosing class. It should have a single constructor, whose parameter type is the
enclosing class. This constructor merely copies the data from its argument: it need
not do any consistency checking or defensive copying. By design, the default
serialized form of the serialization proxy is the perfect serialized form of the
enclosing class. Both the enclosing class and its serialization proxy must be
declared to implement 
Serializable
.
For example, consider the immutable 
Period
class written in Item 50 and
made serializable in Item 88. Here is a serialization proxy for this class. 
Period
is
so simple that its serialization proxy has exactly the same fields as the class: