Customizing a Java framework or library requires the use of certain tools and resources to modify, test, and document the code. An integrated development environment (IDE) is a software application that provides comprehensive features and tools for developing Java code. Popular IDEs include Eclipse, IntelliJ IDEA, NetBeans, and Visual Studio Code. Version control systems (VCS) are software tools that help manage and track changes to the code. Git, Subversion, and Mercurial are popular VCS for Java. Build tools automate the process of compiling, packaging, and deploying code, as well as managing dependencies and configurations. Maven, Gradle, and Ant are popular build tools for Java. Testing tools verify and validate the functionality and quality of code by creating and running different types of tests. JUnit, TestNG, and Selenium are popular testing tools for Java. Documentation tools generate and maintain documentation in various formats such as HTML, PDF, or Markdown. Javadoc, Doxygen, and Sphinx are popular documentation tools for Java.