Programmer's Life: Recipe 4.3 Including Tomcat JAR files in the Build File Classpath

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Recipe 4.3 Including Tomcat JAR files in the Build File Classpath

Problem

You
want to establish an Ant classpath that includes various Tomcat
JAR files.

Solution

Use a path-like structure to define the classpath, then refer to this
classpath whenever you need it. Specify the directories where the
necessary JAR files are located with an external properties file.

Discussion

Before you can compile a servlet using Ant, you must ensure that the
servlet API classes are available on the classpath that the Ant build
file is using for compilation. For example, the
<Tomcat-installation-directory>/common/lib
directory contains servlet.jar, which includes
the necessary classes for compiling a servlet. In addition, you might
want to include the mail.jar component from the
same directory to compile a servlet that uses the JavaMail API. A
different
directory�<Tomcat-installation-directory>/common/endorsed�includes
the xmlParserAPIs.jar file, which you might
specify on the classpath to use the associated SAX and DOM XML
programming classes.

Example 4-3 defines a classpath using a
path XML element. A
compile-servlet target further down in the XML
file then uses the defined classpath to compile a servlet.

Example 4-3. Defining a classpath including Tomcat JAR files

<project name="Cookbook" default="compile-servlet" basedir=".">

  <!-- include compiled-servlet and tomcat-dir properties -->
  <property file="global.properties" />
  
<path id="servlet-classpath">
    <fileset dir="${tomcat.dir}/common/lib">
        <include name="*.jar" />
    </fileset>
    <fileset dir="${tomcat.dir}/common/endorsed">
        <include name="*.jar" />
    </fileset>
</path>

<target name="compile-servlet">
    <echo message="Compiling the servlet...."/>
    <javac srcdir="${src}" destdir="${build}">
        <include name="${compiled.servlet}.java" />
                <classpath refid="servlet-classpath "/>
    </javac>
</target>

</project>

Using the path element, the classpath can be
defined similarly to an instance variable of a Java class, and its
value can then be used throughout the build file. The advantage of
this approach is that the classpath may be very complex, but it has
to be defined only once. Whenever there is a need for a classpath in
an Ant file, the
classpath element and its
refid attribute can be used to pull in the defined
classpath. In Example 4-3, the path element is given
a unique ID, "servlet-classpath."
The developer creates this name to uniquely identify the path-like
structure.

Another core type of Ant task is a
fileset. filesets are elements
that represent groups of files. The two nested
filesets in the example have
dir attributes that specify two
directories under the Tomcat installation directory:
./common/lib and
./common/endorsed. These are directories that
contain many important Java libraries, such as
servlet.jar and mail.jar. A
fileset element's nested
include element creates a pattern (with the
name attribute) that specifies the types of files
to include in each fileset. The example includes
all files in the specified directories ending in
".jar".

If you wanted to further refine the types of JAR files that are
included in a fileset, you could use the
fileset's nested
exclude element:

<fileset dir="${tomcat.dir}/common/lib">
     <include name="*.jar" />
     <exclude name="commons*.jar"/>
</fileset>

The pattern "commons*.jar" excludes
all the JAR files from the classpath that begin with the word
"commons," followed by zero or more
characters and a ".jar" suffix.

The compile.servlet target in Example 4-3 echoes a message to the console, then uses the
javac task to compile a servlet.

This
code from Example 4-3 makes two properties that are
defined in another file available to the Ant build file:

<property file="global.properties" />

Here is what the global.properties file looks
like:

tomcat.dir=k:/jakarta-tomcat-4.1.12
compiled.servlet=MyTask
src=.\src
build=.\build

The property compiled.servlet evaluates to the
name of the Java source file that is being compiled. The
tomcat.dir file is the file path to the Tomcat
root directory.

In Example 4-3, the
classpath element is nested inside the
javac task, as in:

<javac srcdir="${src}" destdir="${build}">
        <include name="${compiled.servlet}.java" />
        <classpath refid="servlet-classpath"/>
</javac>

The classpath element's
refid attribute pulls in the
classpath that was defined earlier in the build file (including all
the Tomcat JARs in ./common/lib and
./common/endorsed). The value of the
refid attribute is the id of
the path element
("servlet-classpath"). In other
words, the path element in Example 4-3 represents a classpath; the
element's id or name is
"servlet-classpath."

If it is necessary to add more classes or JARs to the classpath that
you are defining in an Ant file, then add another nested
fileset to the
path element. Example 4-4
adds all of the contents of the build directory
to the classpath defined by Example 4-3 (along with
the Tomcat-related JARs) by adding a third nested
fileset.

Example 4-4. Nesting three filesets in a path structure

<path id="servlet-classpath">

    <fileset dir="${tomcat.dir}/common/lib">
      <include name="*.jar" />
    </fileset>

    <fileset dir="${tomcat.dir}/common/endorsed">
      <include name="*.jar" />
    </fileset>

        <fileset dir="./build"/>

</path>

An idiom that often appears in path-related patterns is
**
, which
means zero or more directories. For example, the following
fileset tag includes all of the files contained in
any nested images folders
(src is a property name pointing to the source
directory of this fileset), no matter how deeply
they are nested:

<fileset dir="${src}">
    <include name="**/images/*"/>
</fileset>

Programmer's Life

Friday, October 23, 2009

Recipe 4.3 Including Tomcat JAR files in the Build File Classpath

Recipe 4.3 Including Tomcat JAR files in the Build File Classpath

Problem

Solution

Discussion

Example 4-3. Defining a classpath including Tomcat JAR files

Example 4-4. Nesting three filesets in a path structure

See Also

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