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Professor Jane who has three tutees, Able, Baker, and Charlie, all of whom have Professor Jane as their tutor. Issues can arise if writeUnshared() and readUnshared() methods are used with these classes as demonstrated in the following noncompliant code example.
Noncompliant Code Example
This noncompliant code example attempts to serialize the data from the example above using writeUnshared(). However, when the data is deserialized using readUnshared(), the checkTutees() method no longer returns true because the tutor objects of the three students are different from the original Professor object.
| Code Block | ||
|---|---|---|
| ||
String filename = "serial";
try {
// Serializing using writeUnshared
ObjectOutputStream oos = new ObjectOutputStream
(new FileOutputStream(filename));
oos.writeUnshared(jane);
oos.close();
// Deserializing using readUnshared
ObjectInputStream ois = new ObjectInputStream
(new FileInputStream(filename));
Professor jane2 = (Professor)ois.readUnshared();
ois.close();
System.out.println("checkTutees returns: " +
jane3.checkTutees());
// prints "checkTutees returns: false"
} catch(Exception e) {
System.out.println("Exception during deserialization" + e);
} |
Compliant Solution
This compliant solution overcomes the problem of the noncompliant code example by using writeObject() and readObject(), ensuring that the tutor object referred to by the three students has a one-to-one mapping with the original Professor object.
| Code Block | ||
|---|---|---|
| ||
String filename = "serial";
try {
System.out.println("Serializing using writeObject");
ObjectOutputStream oos = new ObjectOutputStream
(new FileOutputStream(filename));
oos.writeObject(jane);
oos.close();
System.out.println("Deserializing using readObject");
ObjectInputStream ois = new ObjectInputStream
(new FileInputStream(filename));
Professor jane2 = (Professor)ois.readObject();
ois.close();
System.out.println("checkTutees returns: " +
jane2.checkTutees());
// prints "checkTutees returns: true"
} catch(Exception e) {
System.out.println("Exception during deserialization" + e);
}
|
Applicability
Using the writeUnshared() and readUnshared() methods may produce unexpected results.
Automated detection is straightforward.
Bibliography
[API 2011] | Classes ObjectOutputStream and ObjectInputStream |
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