To set up the Struts 2 development environment in Java, you need to follow these steps:

1. Download and install Java: Struts 2 is a Java-based web application framework, so you need to install the latest version of Java Development Kit (JDK) on your computer. You can download it from the official website of Oracle or OpenJDK.

2. Download and install Apache Tomcat: Apache Tomcat is a popular web server that supports the Java Servlet and JavaServer Pages (JSP) technologies. You can download the latest version of Apache Tomcat from its official website and install it on your computer.

3. Download and install Struts 2: Once you have installed Java and Apache Tomcat, you need to download the latest version of Struts 2 from its official website. The downloaded file will be in a compressed format, so you need to extract it to a folder on your computer.

4. Create a new Struts 2 project: To create a new Struts 2 project, you need to use an Integrated Development Environment (IDE) such as Eclipse, IntelliJ IDEA, or NetBeans. You can create a new web application project and add the required Struts 2 libraries to the project.

5. Configure the project: You need to configure the Struts 2 project by adding the required configuration files, such as struts.xml, web.xml, and log4j.properties. These files contain the necessary settings and configurations for the Struts 2 framework to work properly.

6. Run the project: Once the project is configured, you can run it on Apache Tomcat. You can start the Apache Tomcat server from the IDE or from the command line, and then access the application using a web browser.

Overall, setting up the Struts 2 development environment requires downloading and installing Java, Apache Tomcat, and Struts 2, creating a new project, and configuring the project. Once the environment is set up, you can start building web applications using Struts 2.