How to hot deploy Java EE applications in Docker containers

I know this question is a little old but I want to share my knowledge about how to develop java EE apps with a tomee server in Docker.

Preparing the Docker image

The first thing to do is to enable logging. I use the official base image and redirect the logs to stdout in order to see it on my console:

# you can change the base image of courseFROM tomee:8-jre-1.7.5-jaxrsRUN ln -s /dev/stdout /usr/local/tomee/logs/catalina.out RUN echo '<?xml version="1.0" encoding="utf-8"?><tomcat-users><role rolename="tomee-admin"/><user username="tomee" password="tomee" roles="tomee-admin,manager-gui,manager-script"/></tomcat-users>' > /usr/local/tomee/conf/tomcat-users.xml

The log addition may not seem like a big deal but it is. With this enabled, you are able to see the success (or failure) of your deployment imediately.The ugly xml snippet is actually very important. It enables a user named tomee with all important permissions to deploy applications.

You can build the image with ordinary docker tooling:

docker build -t tomee-dev .

Preparing the development environment

I use a standard maven directory layout. Here is an example:

pom.xmlsrc | - main    |    - java    |   |    |   - boundary    |        |    |        - TestResource.java    - webapp        |        - WEB-INF            |            - web.xml

The content of those files can be found at the bottom of this answer.

Start the container like this:

docker run -it --rm -p 8080:8080 tomee-dev

The last piece of the puzzle is our maven configuration. You can use the tomee maven plugin for redeployment

<build>    <plugins>        <plugin>            <groupId>org.apache.tomcat.maven</groupId>            <artifactId>tomcat7-maven-plugin</artifactId>            <version>2.2</version>            <configuration>                <url>http://localhost:8080/manager/text</url>                <username>tomee</username>                <password>tomee</password>                                    <path>/${project.artifactId}</path>            </configuration>        </plugin>    </plugins></build>

You can now use mvn clean tomcat7:deploy and mvn clean tomcat7:redeploy commands to deploy/redeploy your application.

Appendix

here is the content of the source and config files I used in the example:

src/main/java/boundary/TestResource.java

import javax.ws.rs.GET;import javax.ws.rs.Path;import javax.ws.rs.core.Response;@Path("/")public class TestResource {    @GET    @Path("test")    public Response test1() {        return Response.ok("this is a test").build();    }}

src/main/java/webapp/WEB-INF/web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://java.sun.com/xml/ns/javaee"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"         version="3.0">    <module-name>hot-deploy</module-name>    <servlet>        <servlet-name>javax.ws.rs.core.Application</servlet-name>        <load-on-startup>1</load-on-startup>    </servlet>    <servlet-mapping>        <servlet-name>javax.ws.rs.core.Application</servlet-name>        <url-pattern>/resources/*</url-pattern>    </servlet-mapping></web-app>

pom.xml

<?xml version="1.0" encoding="UTF-8"?><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/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0</modelVersion>    <artifactId>hot-reload</artifactId>    <groupId>org.test.stackoverflow.answers</groupId>    <version>1.0.0-snapshot</version>    <packaging>war</packaging>    <properties>        <maven.compiler.source>1.8</maven.compiler.source>        <maven.compiler.target>1.8</maven.compiler.target>        <tomee-plugin.pwd>tomee</tomee-plugin.pwd>        <tomee-plugin.user>tomee</tomee-plugin.user>    </properties>    <dependencies>        <dependency>            <groupId>javax</groupId>            <artifactId>javaee-api</artifactId>            <scope>provided</scope>            <version>7.0</version>        </dependency>    </dependencies>    <build>        <plugins>            <plugin>                <groupId>org.apache.tomcat.maven</groupId>                <artifactId>tomcat7-maven-plugin</artifactId>                <version>2.2</version>                <configuration>                    <url>http://localhost:8080/manager/text</url>                    <username>tomee</username>                    <password>tomee</password>                                        <path>/${project.artifactId}</path>                </configuration>            </plugin>        </plugins>    </build></project>

If you mount the host's volume to a few containers read-only, make sure tomcat does not "explode" the war files, at least not to the same folder, then I think you have the hot-deployment, at least to the level tomcat can support. Replacing the .war file in the host folder should trigger a redeploy.