Maven dependent mechanism

Outline

Automatically download all the necessary dependencies in Maven dependent mechanism of help, and keep the version upgrade. Let's look at a case study to learn how it works. Suppose you want to use Log4j as the logging project. What are you doing here?

The traditional way

• Access http://logging.apache.org/log4j/
• Download the Log4j jar library
• Copy the jar to the project classpath
• Manual to include it to rely project
• The management needs to do everything all by themselves

If there Log4j version upgrade, you need to repeat the above steps once.

Maven way

• You need to know Maven coordinates log4j, for example:

    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>

• It will automatically download the 1.2.17 version of log4j library

• Statement Maven pom.xml file is converted into coordinates

    <dependencies>
        <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
        </dependency>
    </dependencies>

• When Maven build or construct, log4j will automatically download the jar and put it in the local Maven repository

• All managed by Maven

explain

See the difference? So in the end what happened in Maven? When creating a Maven project, pom.xml file will be parsed, if you see Maven coordinates log4j, and then Maven search log4j library in this order:

• In the local repository search log4j Maven
• In the Maven central repository search log4j
• (If defined in pom.xml) in Maven remote repository search log4j

Maven dependencies management is a very good tool for you to save a lot of work