chapter 12. jdbc

this chapter covers jdbc ( java database connectivity), which is a set of classes and methods available for the java programming language. the use of jdbc with java is a simple, generic, and portable way of interacting with different types of databases. for this chapter, some existing knowledge of how to program in java is assumed.

the jdbc interfaces, defined by sun, cover all of the interactions you can have with a standard sql database. the vendor (in this case, postgresql) supplies concrete implementations that implement these interfaces. these concrete implementations handle the vendor-specific interactions with the database: connecting, logging in, using stored procedures, and so forth. these interfaces are designed this way so that a program using jdbc can connect to any jdbc-compliant database, without your having to rewrite the code. however, there are some caveats.

one issue is that jdbc does not do any client-side sql parsing or syntax checking. sql statements are passed off transparently to the database, whether or not they are valid. therefore, if the sql is valid on one vendor's database, but invalid on another vendor's database the implementation won't know until the actual connection is made and the sql is sent across. sun is attempting to deal with this problem, and there may be some provisions made to correct this, either in later versions of jdbc or in a different standard.

another issue is that each vendor has additional helper classes specific to that vendor. for instance, postgresql has extensions for geometric data types. other vendors won't support these extensions; they are specific to postgresql. if you use such vendor-specific classes, your program will not work with another jdbc database, despite using the jdbc "standard."

one advantage of the postgresql jdbc driver is that it is a "type 4" driver. this means that it is written in pure java, so it can be taken anywhere, and used anywhere as long as the platform it is used on has tcp/ip capabilities, because the driver only connects via tcp/ip.