You can use DB2's JDBC support to build both:
If your application or applet uses JDBC, you need to familiarize yourself with the JDBC specification, JDBC: A Java SQL API available from Sun Microsystems. This specification describes how to call JDBC APIs to access a database and manipulate data in that database.
You should also read through this section to learn about DB2's extensions to JDBC and its few limitations (refer to "Extensions"). If you plan to create UDFs or stored procedures in Java, refer to "Creating and Using Java User-Defined Functions" and "Creating and Using Java Stored Procedures", as there are considerations that are different for Java than for other languages.
To help you begin coding your program, sample applications and applets are provided in the sqllib/samples/java directory. If you have created the SAMPLE database, you can also run the samples. See the SQL Reference for your platform for information about the SAMPLE database.