Justin Cave is correct that this can lead to redundant data, but this really depends on how you design your database.
The approach of serializing a whole object into a blob is not as outrageous as most people here think it is. In fact, for some applications, this can be the best design you can do, as I explained here: https://stackoverflow.com/a/12644223/1121352.
Indeed, serializing an object leads to at least two benefits:
1- Reducing impedence mismatch: some Java types are just not available in SQL, particularly if you use a lot of classes and custom types, thus converting back and forth from Java objects to SQL can be a huge hassle, and even lead to ambiguities.
2- More flexibility in your schema. Indeed, relational schemas are really great for data that share the same structure, but if some of your objects within a single class can have different properties depending on conditions at runtime, relational schemas can hamper your workflow significantly.
Thus, there certainly are benefits to this approach (at least these two, but certainly others I did not cite), but of course the huge cost to pay is that you lose almost all relational schemas benefits.
However, you can get the best of both worlds if you design carefully your database: you can still set a relational schema (ie: unique key columns) by using the attributes that are unique for each object, and then store the object in the blob. This way, you can still ensure fast retrieval of your object given some unique identifier that is defined by your object's attributes, also reducing redundancy, while you annihilate the impedence mismatch and keep full flexibility of Java objects.
As a side note, there are a few attempts by some DB makers to blend relational and object models together, like the JSON datatype in PostSQL and PostgreSQL so that you can directly process JSON just like any relational column, and also SQL3 and OQL (Object Query Language) to add (limited) objects support into SQL.
In the end, this is all a matter of design and compromise between the relational model and object model.
/EDIT after reading comments: of course, if your data must be searchable ("queryable"), you should NOT store your data as a blob. But if some parts of your data are not meant to be searchable, but rather some kind of meta-data, then storing this data part as an object inside a blob can be a good solution, especially if this meta-data has a flexible structure and can change from object to object.