Wagon HTTP(S) transport

From Maven 3.0.4 onwards, Wagon HTTP(S) transport is based on Apache HTTP client 4.1.2. This also added the HTTP connection pooling support. By default, the connection pool size is 20 per destination. Wagon HTTP transport can be further tuned via settings.xml.

Maven artifact repositories can be defined in the application POM and will also inherit from the super POM file. The super POM file has defined the following repository with the id central tag:

<repositories>
  <repository>
    <snapshots>
      <enabled>false</enabled>
    </snapshots>
    <id>central</id>
    <name>Central Repository</name>
    <url>http://repo.maven.apache.org/maven2</url>
  </repository>
</repositories>

As the connectivity to the repository defined in the previous configuration is over HTTP, Wagon will use its HTTP implementation. You can see that the value of the url element is set to an HTTP endpoint.

The Wagon HTTP connection can be configured per repository by its id via MAVEN_HOME/conf/settings.xml. If we want to change the read timeout period of the HTTP connection to the previous Maven repository with the id central tag, add the following child element under the <servers/> element. The value of the readTimeout element defines the timeout period in milliseconds. If needed, the timeout can be defined per HTTP verb. Here, it's defined only for HTTP GET. The value of the id element must match with what is defined under <repository> element in the pom.xml file.

<server>
  <id>central</id>
  <configuration>
    <httpConfiguration>
      <get>
 <readTimeout>100000</readTimeout>
 </get>
    </httpConfiguration>
  </configuration>
</server>

How about the connection timeout? The connection timeout is different from the connection read timeout, as discussed before. The connection timeout is the waiting time to make the initial connection, while the connection read timeout is the waiting time to read data from the connection after it is established. The following configuration shows how to change the default connection timeout. The value of the connectionTimeout element is defined in milliseconds:

<server>
  <id>central</id>
  <configuration>
    <httpConfiguration>
      <get>
 <connectionTimeout>100000</connectionTimeout> 
 </get>
    </httpConfiguration>
  </configuration>
</server>

There can be a case where a remote repository server expects certain HTTP headers in the request. To add custom headers, you can have the following configuration:

<server>
  <id>central</id>
  <configuration>
    <httpHeaders>
 <httpHeader>
 <name>CUSTOM_HEADER_NAME</name>
 <value>CUSTOM_HEADER_VALUE</value>
 </httpHeader>
    </httpHeaders>
  </configuration>
</server>

As we discussed before, Wagon HTTP(S) transport is based on Apache HTTP client 4.1.2. Apache HTTP client has many configuration parameters to alter its default behavior. Any of these parameters can be configured in Wagon HTTP transport for Maven, as shown in the following configuration:

<server>
  <id>central</id>
  <configuration>
    <httpConfiguration>
      <get>
        <params>
          <param>
 <name>PARAM_NAME</name>
 <value>PARAM_VALUE</value>
 </param>
        </params>
      </get>
    </httpConfiguration>
  </configuration>
</server>

To ask an HTTP client to ignore cookies for all HTTP GET requests, you need to set the value of http.protocol.cookie-policy to ignore:

<server>
  <id>central</id>
  <configuration>
    <httpConfiguration>
      <get>
        <params>
          <param>
 <name>http.protocol.cookie-policy</name>
 <value>ignore</value>
 </param>
        </params>
      </get>
    </httpConfiguration>
  </configuration>
</server>

Wagon system properties

Maven Wagon's default behavior can be altered with the following system properties: