What are the default values for @QueryParam when @DefaultValue is not specified?

Short answer

The parameter values will be:

• valString: null
• valInt: 0
• valBool: false

A bit longer answer

Quoting the Java EE 7 tutorial about extracting request parameters:

If @DefaultValue is not used in conjunction with @QueryParam, and
the query parameter is not present in the request, the value will be
an empty collection for List, Set, or SortedSet; null for
other object types; and the default for primitive types.

The default values for primitive types are described in the Java Tutorials from Oracle:

 Primitive       Default Value
-------------------------------
 byte            0
 short           0
 int             0
 long            0L
 float           0.0f
 double          0.0d
 char            '\u0000'
 boolean         false

As you already know, this behavior can be changed by using the @DefaultValue annotation as following:

@GET
@Path("/foo")
public String myMethod(@DefaultValue("foo") @QueryParam("valString") String valString,
                       @DefaultValue("1") @QueryParam("valInt") int valInt,
                       @DefaultValue("true") @QueryParam("valBool") boolean valBool) {
    ....
}