Building Web Applications with Maven 2[转自官网]

官网：http://today.java.net/pub/a/today/2007/03/01/building-web-applications-with-maven-2.html

 

You may have heard of Maven 2--it's often touted by
technologists as a replacement for Ant. You may have even taken
some time to browse around on the Maven 2 site , but
maybe the documentation has left you a little bit unclear on where and
how to go about getting started.

In this article, we will take a look at using Maven 2 to help
build a simple web application (a bit of business logic in a JAR
and a JSP-based web application). By the end of this article, you
should feel comfortable working with Maven 2, and ready to start
using it as a much more satisfactory tool than Ant (or even your
IDE).

Getting Started

These instructions assume that you have installed Java 5 and Maven
2 . The following two commands shown should work at your command
line:

C

:

\&gt

;

java 

-

version


 java version 

"1.5.0_06"


 

Java

(

TM

)

 

2

 

Runtime

 

Environment

,

 

Standard

 

Edition

 

(

build 

1.5

.

0_06

-

b05

)


 

Java

 

HotSpot

(

TM

)

 

Client

 VM 

(

build 

1.5

.

0_06

-

b05

,

 mixed mode

,

 sharing

)



C

:

\&gt

;

mvn 

-

v


Maven

 version

:

 

2.0

.

5

Everything else required for this project will be downloaded for
you automatically by Maven 2 (obviously, a working internet
connection is also required). I used my Windows system to write
this article, but everything here should work fine on Mac OS X,
Linux, Solaris, etc.

From a high level, the project will be organized into two
subprojects (one for the JAR and one for the WAR). Let's start by
creating the base directory for the project. This directory serves
as the base for the other folders.

C

:

\&gt

;

mkdir maven2example


C

:

\&gt

;

cd maven2example


C

:

\maven2example

&

gt

;

Now, let's create the two subprojects. Maven 2 supports the
notion of creating a complete project template with a simple
command. The project templates (called “archetypes” in
Maven) shown below are a subset of the full list of archetypes built in to Maven 2.

Project Template (Archetype)	Purpose
maven-archetype-archetype	Create your own project template (archetype).
maven-archetype-j2ee-simple	Creates a J2EE project (EAR), with directories and subprojects for the EJBs, servlets, etc.
maven-archetype-mojo	Create your own Maven 2 plugins.
maven-archetype-quickstart	Simple Java project, suitable for JAR generation. Maven 2 default.
maven-archetype-site	Documentation-only site, with examples in several formats. You can run this archetype on top of an existing Maven 2 project to add integrated documentation.
maven-archetype-webapp	Creates a web application project (WAR), with a simple Hello World JSP.

These archetypes are analogous to the sample projects you might
find in your IDE as defaults for standard "New
Project…" options.

To create a simple Java project, you simply execute the command
as shown.

mvn archetype

:

create


   

-

DgroupId

=[

your project

's group id]


   -DartifactId=[your project'

s artifact id

]

The mvn command invokes the Maven 2 system, in this
case a request to run the archetype plugin with the
create command. The - D commands are simply setting
Java system properties, thereby passing configuration information
to Maven 2. Per the Maven 2 FAQ, the groupID should
follow the package name (reversed DNS of your website), and can
contain subgroups as appropriate. For example, the sample code for
my books might use com . cascadetg . hibernate or
com . cascadetg . macosx . In this case, let's use the
com . attainware . maven2example .

The artifactID is specific to each artifact and by
convention should be the filename, excluding extension. In this
case, we would like to create two artifacts, a JAR file containing
the logic and a WAR file containing the web application. First,
let's create the JAR file using the command as shown below. Maven 2
tends to be quite verbose, and so I have trimmed the output shown
here and and many of the other listings in this article to focus on
the elements of interest.

<b>

C:\maven2example&gt;mvn archetype:create


       -DgroupId=com.attainware.maven2example


     -DartifactId=maven2example_logic



</b>

[INFO]   Scanning for projects...


[INFO] Searching repository for plugin with prefix: 'archetype'.


[INFO]   -----------------------------------------------------


[INFO] Building Maven Default Project


   

<i>

&lt;snip&gt;


</i>

[INFO] Archetype created in dir:   


                        C:\maven2example\maven2example_logic


[INFO]   -----------------------------------------------------


[INFO] BUILD SUCCESSFUL


[INFO]   -----------------------------------------------------


[INFO] Total time: 1 second


[INFO] Finished at: Sun Feb 04 10:42:33 PST 2007


[INFO] Final Memory: 4M/8M


[INFO]   -----------------------------------------------------



C:\maven2example&gt;

Looking at the resulting file structure, we can see that Maven 2
has done several things for us. It's created a fairly complete
directory structure, following many best practices for organizing
code. The source code is broken into two directories, one for the
code itself and one for the test cases. The package structure is
taken from the groupId , and is mirrored in both the
main code and the test case directory structure.

Figure 1. Source for JAR project layout

Clicking through the results, you will see folders and two Java
source files--so far, nothing surprising.

In the root folder, however, we notice a file called pom.xml .

Figure 2. Maven 2 project file for JAR project

This file is essentially analogous to an IDE project file: it
contains all of the information about a project, and is the file
that Maven 2 uses to act upon to execute commands. The contents of
pom.xml :

&

lt

;

project xmlns

=

 

http

:

//maven.apache.org/POM/4.0.0




      xmlns

:

xsi

=

"http://www.w3.org/2001/XMLSchema-instance"


        xsi

:

schemaLocation

=

"http://maven.apache.org/POM/4.0.0   


       

http://maven.apache.org/maven-v4_0_0.xsd"

&

gt

;




     

&

lt

;

modelVersion

&

gt

;

4.0

.

0

&

lt

;

/modelVersion>


     <groupId>com.attainware.maven2example</

groupId

&

gt

;


        

&

lt

;

artifactId

&

gt

;

maven2example_logic

&

lt

;

/artifactId>


     <packaging>jar</

packaging

&

gt

;


     

&

lt

;

version

&

gt

;

1.0

-

SNAPSHOT

&

lt

;

/version>


     <name>maven2example_logic</

name

&

gt

;


     

&

lt

;

url

&

gt

;

http

:

//maven.apache.org</url>


     

&

lt

;

dependencies

&

gt

;


       

&

lt

;

dependency

&

gt

;


         

&

lt

;

groupId

&

gt

;

junit

&

lt

;

/groupId>


         <artifactId>junit</

artifactId

&

gt

;


           

&

lt

;

version

&

gt

;

3.8

.

1

&

lt

;

/version>


         <scope>test</

scope

&

gt

;


       

&

lt

;

/dependency>


     </

dependencies

&

gt

;


 

&

lt

;/

project

&

gt

;

There really isn't a lot in the standard pom.xml file. We
can see the groupId and artifactId , that
the project is intended to build a JAR, and that the current
version is to 1.0-SNAPSHOT. The project uses JUnit 3.8.1 for unit
tests. We could change the URL to point to our company or project
website and/or update the version number to something more
appropriate, but for now this is fine. If you are curious, you can
review the schema for Maven pom.xml files.

Maven 2 makes heavy use of standard directory layouts to reduce
clutter. It assumes that the source code and test code will be
found in the directory created by the project template. By
specifying standard directory layouts , it easier to immediately start work on a project with spending a lot of time relearning the build
process. While it is possible to reconfigure Maven 2 to use custom
directory layouts, I have found that it's generally less work to
simply use the Maven 2 layout. I have converted several projects of
small to medium size from Ant to Maven 2, and found that the size
and complexity of my build files (from custom Ant build.xml
files to Maven 2 pom.xml files) dropped by an order of magnitude.
By using Maven 2 templates (archetypes) and simply copying source
files into the proper locations, I found that I wound up with much
more comprehensible project structures than the slowly accreted,
custom Ant build.xml projects. While it is possible to force Maven
2 to fit into arbitrary directory structures, that's probably not
the place to start.

Maven 2 Commands

Maven 2 supports two kinds of commands that can be run on
projects (pom.xml files). The first type of command is a
plugin command. Plugin commands include things like "copy a
set of files," "compile a source tree," etc. The other type of
command is a lifecycle command. A lifecycle command is a
series of plugin commands strung together. For example, the test
lifecycle command might include several plugin commands in a
series.

Let's execute the lifecycle command mvn
test on our pom.xml file. As can
be seen in the following listing, this command executes several
plugins (additional output omitted for readability).

C

:

\maven2example\maven2example_logic

&

gt

;

mvn test



[

INFO

]

 

Scanning

 

for

 projects

...


[

INFO

]

   

-------------------------------------------------------


[

INFO

]

 

Building

 maven2example_logic


[

INFO

]

    task

-

segment

:

 

[

test

]


[

INFO

]

   

-------------------------------------------------------


<b>

[

INFO

]

 

[

resources

:

resources

]


[

INFO

]

 

[

compiler

:

compile

]


[

INFO

]

 

[

resources

:

testResources

]


[

INFO

]

 

[

compiler

:

testCompile

]


[

INFO

]

 

[

surefire

:

test

]


</

b

>[

INFO

]

   

------------------------------------------------------


[

INFO

]

 BUILD SUCCESSFUL



C

:

\maven2example\maven2example_logic

&

gt

;

What we can see is that the mvn test lifecycle
command is bound to several plugins, including
resources , compiler , and
surefire . These plugins in turn are called with
different goals, such as compile or
testCompile . So, by simply calling mvn
with a single lifecycle command, we execute a number of plugins--no additional configuration necessary. If you want to specify a
plugin directly, that's fine. For example:

C

:

\maven2example\maven2example_logic

&

gt

;

mvn compiler

:

compile



[

INFO

]

 

Scanning

 

for

 projects

...


[

INFO

]

 

Searching

 repository 

for

 plugin 

with

 prefix

:

 

'compiler'

.


[

INFO

]

 

--------------------------------------------------------


[

INFO

]

 

Building

 maven2example_logic


[

INFO

]

    task

-

segment

:

 

[

compiler

:

compile

]


[

INFO

]

 

--------------------------------------------------------


[

INFO

]

 

[

compiler

:

compile

]


[

INFO

]

 

Nothing

 to compile 

-

 all classes are up to date


[

INFO

]

 

--------------------------------------------------------


[

INFO

]

 BUILD SUCCESSFUL


[

INFO

]

 

--------------------------------------------------------



C

:

\maven2example\maven2example_logic

&

gt

;

Now that we have seen both lifecycle commands and plugin
commands in action, let's look at some of the typical lifecycle
commands.

mvn clean	Cleans out all Maven-2-generated files.
mvn compile	Compiles Java sources.
mvn test-compile	Compiles JUnit test classes.
mvn test	Runs all JUnit tests in the project.
mvn package	Builds the JAR or WAR file for the project.
mvn install	Installs the JAR or WAR file in the local Maven repository (use this if you have multiple interdependent local projects).

A complete list of lifecycle commands can be found at on the Maven 2 site.

Similarly, here is a list of some of the more popular plugin
commands, analogous to the popular tasks in Ant or commands in an
IDE. Note that a lifecycle command name is a single word, whereas
a plugin command name is broken into a plugin and a specific goal
with a colon:

clean:clean	Cleans up after the build.
compiler:compile	Compiles Java sources.
surefire:test	Runs the JUnit tests in an isolated classloader.
jar:jar	Creates a JAR file.
eclipse:eclipse	Generates an Eclipse project file from the pom.xml file.

You may want to take some time perusing the list of plugins
that are available to Maven 2 by default. It is possible to add
additional plugins by either writing them yourself or by grabbing
them from a repository (repositories are discussed later in this
article).

You can configure plugins on a per-project basis by updating
your pom.xml file. For example, if you wish to force compilation
on Java 5, simply pass in the following option under the build
configuration in the pom.xml file:

&

lt

;

project xmlns

=

"http://maven.apache.org/POM/4.0.0"

 


xmlns

:

xsi

=

  

"http://www.w3.org/2001/XMLSchema-instance"

 


xsi

:

schemaLocation

=

  

"http://maven.apache.org/POM/4.0.0   


http://maven.apache.org/maven-v4_0_0.xsd"

&

gt

;


       

&

lt

;

build

&

gt

;


         

&

lt

;

plugins

&

gt

;


           

&

lt

;

plugin

&

gt

;


              

&

lt

;

groupId

&

gt

;

org

.

apache

.

maven

.

plugins

&

lt

;

/groupId>


              <artifactId>maven-compiler-plugin</

artifactId

&

gt

;


              

&

lt

;

configuration

&

gt

;


                   

&

lt

;

source

&

gt

;

1.5

&

lt

;

/source>


                   <target>1.5</

target

&

gt

;


              

&

lt

;

/configuration>


           </

plugin

&

gt

;


         

&

lt

;

/plugins>


       </

build

&

gt

;


 

&

lt

;/

project

&

gt

;

Each plugin listed on the Maven 2 site includes documentation on the various configuration options available.

Maven 2 Versus Ant?

If you are familiar with Ant, you may be wondering why
lifecycles and plugins are an improvement over targets and tasks.
While you can cleanly separate your Ant targets from the various
directories and artifacts, it's surprisingly difficult to do. For
example, let's say that you have several directories, with several
artifacts (multiple JAR files, which get combined into a WAR, for
example). Every command that you write for each Ant target will
require properties for the source, and various dependencies,
typically passed around via a combination of Ant variables.
Dependencies in particular require a lot of custom handholding,
with JAR files downloaded and managed by hand.

Maven 2, on the other hand, assumes that given a pom.xml file, you
are probably always going to be doing the same general kind of
things with your code. You are probably going to want to build a
JAR file from that lump of code over there . You are probably
going to want to build a WAR file from that set of files over
there . So those actions (or goals) are written in Java as
reusable chunks of code (plugins). Instead of complicated lumps of
thousands of lines of custom build.xml files, you just call a
plugin with a specific goal.

There are several advantages to this approach. For one, the
Maven 2 Java-based plugins are a lot smarter than the lower-level
commands found in Ant tasks. You don't have to write custom tasks
that handle compilation, and then have to worry about keeping your
clean task in sync with your compile and packaging tasks; Maven 2
just takes care of this stuff for you.

Another advantage of this model is that it encourages reuse of
plugins in a much more robust way than Ant tasks. Later in this
article, we will show how simply adding a few lines to a pom.xml
file will automatically download and launch Jetty (a lightweight
servlet/JSP container), seamlessly installing and running the WAR
file.

Adding Some Business Logic

Let's add a tiny bit of pseudo-business logic to our
application. First, we write a simple test cast that looks for a
String, updating C:\maven2example\maven2example_logic\src\test\java\com\attainware\maven2example\AppTest.java .

 

package

 com

.

attainware

.

maven2example

;


 

import

 junit

.

framework

.

Test

;


 

import

 junit

.

framework

.

TestCase

;


 

import

 junit

.

framework

.

TestSuite

;


 

import

 com

.

attainware

.

maven2example

.

App

;


 


 

public

 

class

 

AppTest

 

extends

 

TestCase


 

{


       

public

 

void

 testApp

()

  


       

{


           assertTrue

(

 

App

.

now

().

length

()

 

&

gt

;

 

0

 

);


       

}


 

}

Opening the file
C:\maven2example\maven2example_logic\src\main\java\com\attainware\maven2example\App.java ,
we update the contents to:

package

 com

.

attainware

.

maven2example

;



public

 

class

 

App


{


       

public

 

static

 

String

 now

()


       

{


            

return

 

new

 java

.

util

.

Date

().

toString

();

  


       

}


 

}

Running the command mvn install , as shown below,
causes several plugins to run (status messages omitted for
readability).

 C

:

\maven2example\maven2example_logic

&

gt

;

mvn install



 

[

INFO

]

 

[

resources

:

resources

]


 

[

INFO

]

 

[

compiler

:

compile

]


 

[

INFO

]

 

[

resources

:

testResources

]


 

[

INFO

]

 

[

compiler

:

testCompile

]


 

[

INFO

]

 

[

surefire

:

test

]


 

[

INFO

]

 

[

jar

:

jar

]


 

[

INFO

]

 

[

install

:

install

]


 

[

INFO

]

 BUILD SUCCESSFUL



 C

:

\maven2example\maven2example_logic

&

gt

;

By running the mvn install lifecycle command, Maven
2 finishes by installing the JAR file into the local repository,
making this resulting JAR file available to other projects on this
system. This allows this JAR file to be available for inclusion in
our WAR file.

Creating the WAR file

Now that we have created our JAR file, creating the WAR file is
straightforward--we just pass in a different archetype ID.

C

:

\maven2example

&

gt

;<

b

>

mvn archetype

:

create


   

-

DgroupId

=

com

.

attainware

.

maven2example


   

-

DartifactId

=

maven2example_webapp


   

-

DarchetypeArtifactId

=

maven

-

archetype

-

webapp

</

b

>



[

INFO

]

 

Scanning

 

for

 projects

...


[

INFO

]

 

Searching

 repository 

for

 plugin 

with

 prefix

:

 

'archetype'

.


[

INFO

]

 

---------------------------------------------------------


[

INFO

]

 

Building

 

Maven

 

Default

 

Project


[

INFO

]

 

[

archetype

:

create

]


[

INFO

]

 

Archetype

 created 

in

 dir

:

 


                        C

:

\maven2example\maven2example_webapp


[

INFO

]

 

---------------------------------------------------------


[

INFO

]

 BUILD SUCCESSFUL


[

INFO

]

 

---------------------------------------------------------



C

:

\maven2example

&

gt

;

As shown in Figure 3, we now have a directory structure you
would expect to see for a WAR. Note that the JAR file is
automatically pulled into the WAR file from the local
repository.

Figure 3. WAR project directory structure

Simply executing the command mvn package creates
our WAR file (again, omitting most of the status messages besides
the plugin list).

In this case, the mvn package command builds the
WAR file but does not install it into the local repository
(repositories will be discussed later). As you build larger, more
sophisticated projects with more complex dependencies, you may wish
to be more deliberate about using the mvn package and
mvn install commands to control inter-project
dependencies. Because the WAR file is the final artifact we are
creating, we can save a few compute cycles merely by packaging the
WAR file in the local target directory.

 C

:

\maven2example\maven2example_webapp

&

gt

;

mvn 

package



 

[

INFO

]

 

Scanning

 

for

 projects

...


 

[

INFO

]

 

--------------------------------------------------------


 

[

INFO

]

 

Building

 maven2example_webapp 

Maven

 

Webapp


 

[

INFO

]

    task

-

segment

:

 

[

package

]


 

[

INFO

]

 

--------------------------------------------------------


 

[

INFO

]

 

[

resources

:

resources

]


 

[

INFO

]

 

[

compiler

:

compile

]


 

[

INFO

]

 

[

resources

:

testResources

]


 

[

INFO

]

 

[

compiler

:

testCompile

]


 

[

INFO

]

 

[

surefire

:

test

]


 

[

INFO

]

 

[

war

:

war

]


 

[

INFO

]

 

Building

 war

:

 


         C

:

\maven2example\maven2example_webapp\


             target\maven2example_webapp

.

war


 

[

INFO

]

 

-------------------------------------------------------


 

[

INFO

]

 BUILD SUCCESSFUL


 

[

INFO

]

 

-------------------------------------------------------



 C

:

\maven2example\maven2example_webapp

&

gt

;

As we can see in Figure 4, we now have a WAR file.

Figure 4. Resulting WAR file

Now that we have a WAR file, we would like to be able to run the
application. To do this, we simply add the Jetty plugin to the
pom.xml for this web application as shown:

&

lt

;

project xmlns

=

  

"http://maven.apache.org/POM/4.0.0"


   xmlns

:

xsi

=

  

"http://www.w3.org/2001/XMLSchema-instance"


  xsi

:

schemaLocation

=

  

"http://maven.apache.org/POM/4.0.0   


  

http://maven.apache.org/maven-v4_0_0.xsd"

&

gt

;




     

&

lt

;

modelVersion

&

gt

;

4.0

.

0

&

lt

;

/modelVersion>


     <groupId>com.attainware.maven2example</

groupId

&

gt

;


     

&

lt

;

artifactId

&

gt

;

maven2example_webapp

&

lt

;

/artifactId>


     <packaging>war</

packaging

&

gt

;


     

&

lt

;

version

&

gt

;

1.0

-

SNAPSHOT

&

lt

;

/version>


     <name>maven2example_webapp   Maven Webapp</

name

&

gt

;


     

&

lt

;

url

&

gt

;

http

:

//maven.apache.org</url>


     

&

lt

;

dependencies

&

gt

;


       

&

lt

;

dependency

&

gt

;


         

&

lt

;

groupId

&

gt

;

junit

&

lt

;

/groupId>


         <artifactId>junit</

artifactId

&

gt

;


           

&

lt

;

version

&

gt

;

3.8

.

1

&

lt

;

/version>


         <scope>test</

scope

&

gt

;


       

&

lt

;

/dependency>


     </

dependencies

&

gt

;


     

&

lt

;

build

&

gt

;


       

&

lt

;

finalName

&

gt

;

maven2example_webapp

&

lt

;

/finalName>


         <b>&lt;plugins&gt;


             &lt;plugin&gt;


                  &lt;groupId&gt;org.mortbay.jetty&lt;/

groupId

&

gt

;


                  

&

lt

;

artifactId

&

gt

;

maven

-

jetty

-

plugin

&

lt

;

/artifactId&gt;


             &lt;/

plugin

&

gt

;


         

&

lt

;

/plugins&gt;


</

b

>

   

&

lt

;

/build&gt;


 &lt;/

project

&

gt

;

By adding the plugins entry with the Jetty information, we can
now run our web application by simply typing the command as shown
below.

 C

:

\maven2example\maven2example_webapp

&

gt

;<

b

>

mvn jetty

:

run


</

b

>


 

[

INFO

]

 

Scanning

 

for

 projects

...


 

[

INFO

]

 

Searching

 repository 

for

 plugin 

with

 prefix

:

 

'jetty'

.


 

[

INFO

]

   

----------------------------------------------------


 

[

INFO

]

 

Building

 maven2example_webapp 

Maven

 

Webapp


 

[

INFO

]

    task

-

segment

:

   

[

jetty

:

run

]


 

[

INFO

]

   

----------------------------------------------------


 

[

INFO

]

 

Preparing

 jetty

:

run


 

[

INFO

]

 

[

resources

:

resources

]


 

[

INFO

]

 

[

compiler

:

compile

]


 

[

INFO

]

 

[

jetty

:

run

]


 

[

INFO

]

 

Starting

 jetty 

6.1

.

0pre0

   

...


 

[

INFO

]

 

Classpath

 

=

   


   

[

file

:

/C:/

maven2example

/

maven2example_webapp

/

target

/

classes

/]


   

2007

-

02

-

04

 

12

:

41

:

24.015

::

INFO

:


    

Started

 

SelectChannelConnector

 

@

   

0.0

.

0.0

:

8080


 

[

INFO

]

 

Started

 

Jetty

 

Server

We can now open our web browser to localhost:8080/maven2example_webapp
to see our web application (as shown in Figure 5). Type
Ctrl -C in the console window to shut down the
server. Note that we didn't have to download and install Jetty
separately--Maven 2 automatically downloads and configures
Jetty.

Figure 5. Hello World Web Application

Tying Together the Logic and Web Application

Now, we simply have to tie together the logic in our JAR file
and the web application. First, we want to set up a dependency
between our JAR and the web application. This will tell Maven 2
that we want to use this JAR file in our WAR, which will cause
Maven 2 to automatically copy the JAR file when we package our WAR
file.

First, we add the dependency on this other JAR file to our
pom.xml for the web application as shown below.

&

lt

;

project xmlns

=

  

"http://maven.apache.org/POM/4.0.0"


 xmlns

:

xsi

=

  

"http://www.w3.org/2001/XMLSchema-instance"

 


 xsi

:

schemaLocation

=

  

"http://maven.apache.org/POM/4.0.0   


 

http://maven.apache.org/maven-v4_0_0.xsd"

&

gt

;




     

&

lt

;

modelVersion

&

gt

;

4.0

.

0

&

lt

;

/modelVersion>


     <groupId>com.attainware.maven2example</

groupId

&

gt

;


     

&

lt

;

artifactId

&

gt

;

maven2example_webapp

&

lt

;

/artifactId>


     <packaging>war</

packaging

&

gt

;


     

&

lt

;

version

&

gt

;

1.0

-

SNAPSHOT

&

lt

;

/version>


     <name>maven2example_webapp   Maven Webapp</

name

&

gt

;


     

&

lt

;

url

&

gt

;

http

:

//maven.apache.org</url>


     

&

lt

;

dependencies

&

gt

;


       

&

lt

;

dependency

&

gt

;


         

&

lt

;

groupId

&

gt

;

junit

&

lt

;

/groupId>


         <artifactId>junit</

artifactId

&

gt

;


           

&

lt

;

version

&

gt

;

3.8

.

1

&

lt

;

/version>


         <scope>test</

scope

&

gt

;


       

&

lt

;

/dependency>


   <b>    &lt;dependency&gt;


           &lt;groupId&gt;com.attainware.maven2example&lt;/

groupId

&

gt

;


            

&

lt

;

artifactId

&

gt

;

maven2example_logic

&

lt

;

/artifactId&gt;


           &lt;version&gt;1.0-SNAPSHOT&lt;/

version

&

gt

;


       

&

lt

;

/dependency&gt;


</

b

>

     

&

lt

;

/dependencies&gt;


     &lt;build&gt;


       &lt;finalName&gt;maven2example_webapp&lt;/

finalName

&

gt

;


         

&

lt

;

plugins

&

gt

;


              

&

lt

;

plugin

&

gt

;


                

&

lt

;

groupId

&

gt

;

org

.

mortbay

.

jetty

&

lt

;

/groupId&gt;


                &lt;artifactId&gt;maven-jetty-plugin&lt;/

artifactId

&

gt

;


              

&

lt

;

/plugin&gt;


         &lt;/

plugins

&

gt

;


     

&

lt

;

/build&gt;


 &lt;/

project

&

gt

;

We then update our JSP file to use our fancy new business
logic.

&

lt

;

html

&

gt

;


 

&

lt

;

body

&

gt

;


 

&

lt

;

h2

&

gt

;

Fancy

 

Clock

&

lt

;

/h2>


 <%= com.attainware.maven2example.App.now() %>


 </

body

&

gt

;


&

lt

;/

html

&

gt

;

Next, we run the command mvn package to rebuild the
WAR file.

 C

:

\maven2example\maven2example_webapp

&

gt

;

mvn 

package



 

[

INFO

]

 

Scanning

 

for

 projects

...


 

[

INFO

]

   

---------------------------------------------------


 

[

INFO

]

 

Building

 maven2example_webapp 

Maven

 

Webapp


 

[

INFO

]

    task

-

segment

:

   

[

package

]


 

[

INFO

]

   

---------------------------------------------------


 

[

INFO

]

 

[

resources

:

resources

]


 

[

INFO

]

 

[

compiler

:

compile

]


 

[

INFO

]

 

[

resources

:

testResources

]


 

[

INFO

]

 

[

compiler

:

testCompile

]


 

[

INFO

]

 

[

surefire

:

test

]


 

[

INFO

]

 

[

war

:

war

]


 

[

INFO

]

 

Building

 war

:

   


     C

:

\maven2example\maven2example_webapp\


          target\maven2example_webapp

.

war


 

[

INFO

]

   

---------------------------------------------------


 

[

INFO

]

 BUILD SUCCESSFUL


 

[

INFO

]

 

-----------------------------------------------------

Notice that the JAR file is now copied into WAR file, as shown
in Figure 6.

Figure 6. Verifying the JAR copied into the WAR

When we execute the mvn jetty : run command and view
the results in our browser, we see the results as shown in Figure
7.

Figure 7. WAR running with business logic from JAR

To recap, we now have two independent projects running on our
system. When we run mvn install on the logic, the JAR
file installed in the local repository will be updated. When we run
mvn package on the web application, it will pick up
the latest copy installed into the local repository.

We would like to be able to run a single command to update both
the JAR file and the WAR file. To do this, we create another
pom.xml file that invokes both projects.

&

lt

;

project

&

gt

;


     

&

lt

;

name

&

gt

;

Maven

 

2

 

Example

&

lt

;

/name>


         <url>http:/

/

www

.

attainware

.

com

/&

lt

;

/url>


     <modelVersion>4.0.0</

modelVersion

&

gt

;


   


     

&

lt

;

groupId

&

gt

;

com

.

attainware

.

maven2example

&

lt

;

/groupId>


        <version>1.0</

version

&

gt

;


     

&

lt

;

artifactId

&

gt

;

maven2example_package

&

lt

;

/artifactId>


     <packaging>pom</

packaging

&

gt

;


   


     

&

lt

;

modules

&

gt

;


       

&

lt

;

module

&

gt

;

maven2example_logic

&

lt

;

/module>


       <module>maven2example_webapp</

module

&

gt

;


     

&

lt

;

/modules>


 </

project

&

gt

;

This pom.xml file lives right above the other projects
and serves as a "master" project file.

Figure 8. Location of master project file

Now, we can simply execute a single command, mvn install , and do a full build on both projects.

<b>

C:\maven2example&gt;mvn install


</b>


 [INFO] Scanning for   projects...


 [INFO] Reactor build order:


 [INFO]   maven2example_logic


 [INFO]   maven2example_webapp Maven Webapp


 [INFO]   Maven 2   Example


 [INFO]   -----------------------------------------------------


 [INFO] Building maven2example_logic


 [INFO]    task-segment: [install]


 [INFO]   -----------------------------------------------------


 [INFO] [resources:resources]


 [INFO] [compiler:compile]


 [INFO] [resources:testResources]


 [INFO] [compiler:testCompile]


 [INFO] [surefire:test]


 [INFO] [jar:jar]


 [INFO] [install:install]


 [INFO]   -----------------------------------------------------


 [INFO] Building maven2example_webapp Maven Webapp


 [INFO]    task-segment:   [install]


 [INFO]   -----------------------------------------------------


 [INFO] [resources:resources]


 [INFO] [compiler:compile]


 [INFO] [resources:testResources]


 [INFO] [compiler:testCompile]


 [INFO] [surefire:test]


 [INFO] [war:war]


 [INFO] [install:install]


 [INFO] [site:attach-descriptor]


 [INFO] [install:install]


 [INFO]   -----------------------------------------------------


 [INFO] Reactor Summary:


 [INFO]   -----------------------------------------------------


 [INFO] maven2example_logic   ................ SUCCESS [2.281s]


 [INFO] maven2example_webapp Maven Webapp .... SUCCESS [0.563s]


 [INFO] Maven 2 Example   .................... SUCCESS [1.156s]


 [INFO]   -----------------------------------------------------


 [INFO] BUILD SUCCESSFUL


 [INFO] -------------------------------------------------------

To summarize, we now have a project that now compiles and tests
a JAR, which is then built and installed into a WAR, which is then
in turn installed into a local web server (which is downloaded and
automatically configured). All of this with a few tiny
pom.xml files.

Repositories

You may be wondering about the use of the term
"repository." We have glossed over the use of the term,
but in brief, Maven 2 makes use of two kinds of repository: local
and remote. These repositories serve as locations for Maven 2 to
automatically pull dependencies. For example, our pom.xml
file above makes use the local repository for managing the
dependency on the JAR file, and the default Maven 2 remote
repository for managing the dependencies on JUnit and Jetty.

Generally speaking, dependencies come from either the local
repository or remote repositories. The local repository is used by
Maven 2 to store downloaded artifacts from other repositories. The
default location is based on your system. Figure 9 shows the local
repository on my laptop as of the writing of this article.

Figure 9. Local repository example

If Maven 2 can't resolve a dependency in the local repository,
it will try to resolve the dependency using a remote
repository.

The default remote repository, known as Ibiblio , includes many of the most popular open source packages. You can browse the wide range of packages on Ibiblio with the URL above and add dependencies as needed. For example, let's say that you would like to use Hibernate in your project. Navigating to www.ibiblio.org/maven/org.hibernate/poms ,
we can see there are a wide number of releases of Hibernate
available. Opening up a sample Hibernate pom file , we can see that we
simply need to add the appropriate groupId ,
artifactId , and version entries to our
business logic pom.xml file (the scope flag tells Maven 2 which
lifecycle is interested in the dependency).

&

lt

;

dependency

&

gt

;


        

&

lt

;

groupId

&

gt

;

org

.

hibernate

&

lt

;

/groupId>


        <artifactId>hibernate</

artifactId

&

gt

;


        

&

lt

;

version

&

gt

;

3.2

.

1.ga

&

lt

;

/version>


        <scope>compile</

scope

&

gt

;


 

&

lt

;/

dependency

&

gt

;

Simply adding this dependency to the pom.xml file will
cause Maven 2 to automatically download Hibernate and make the
appropriate JAR files available to both the business logic JAR file
and the WAR file.

You can set up your own remote repository, and add an entry to
the pom.xml file to look in that repository for artifacts.
This is extremely useful for enterprises that make use of shared
resources (for example, one group may wish to publish JAR files
that are used to access a particular piece of middleware).

Finally, you may instead wish to install your own JARs into the
local repository. For example, if you have a
Simple.jar file that someone gave you, use the command
shown below (choosing groupId and
artifactId values that are highly likely to be unique
to avoid a namespace collision).

mvn install

:

install

-

file


     

-

Dfile

=

Sample

.

jar


     

-

DgroupId

=

uniquesample


     

-

DartifactId

=

sample_jar


     

-

Dversion

=

2.1

.

3b2


     

-

Dpackaging

=

jar


     

-

DgeneratePom

=

true

Summary

In this article, we looked at how a few commands and some tiny
XML files allow us to create, compile, test, bundle, and manage
project dependencies. We built a simple web application and
deployed it to a web server with just a few commands, and we still
haven't touched on many of the features of Maven 2. For example,
additional commands generate integrated Javadocs across multiple
projects, code coverage reports, or even a complete website with
documentation. With luck, this orientation to Maven 2 has given you
enough information to begin the transition. Eventually, tools such
as Eclipse and NetBeans will almost certainly support Maven 2 (or
something like it) natively. In the meantime, you can dramatically
reduce your use of raw Ant (and spend a lot less time fighting XML
build scripts) by switching even small projects over to Maven
2.