Solving the Missing rt.jar Problem in Java 11 with Maven
How to Download and Use rt.jar with Maven
If you are a Java developer, you may have encountered the need to use rt.jar in your project. This file contains all of the compiled class files for the base Java Runtime Environment, as well as the bootstrap classes that comprise the core Java API. It is essential for running and compiling Java applications, but it is not always easy to find or use it with Maven, a popular tool for managing dependencies and building projects. In this article, we will show you how to download and use rt.jar with Maven, as well as some tips and best practices for avoiding common pitfalls.
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How to Download rt.jar
The first step is to locate the rt.jar file in your system. Depending on your operating system and Java version, it may be in different places. Here are some common locations:
Windows: $JAVA_HOME/jre/lib, where $JAVA_HOME refers to the JDK installation directory.
MacOS: /System/Library/Frameworks//Classes, where refers to the Java version number. This is only true for Java versions prior to JDK 1.7. From Java 7 onwards, Apple has stopped distributing Java and you need to install it separately from Oracle. In that case, the location is /Library/Java/JavaVirtualMachines/jdk.jdk/Contents/Home/jre/lib.
Linux: $JAVA_HOME/jre/lib, where $JAVA_HOME refers to the JDK installation directory.
Once you have found the rt.jar file, you can copy or extract it from the JRE lib directory to your desired location. You can also verify its integrity and version by using tools like jar or unzip. For example, you can run the following command in a terminal or command prompt:
jar tvf rt.jar grep META-INF/MANIFEST.MF
This will print out the manifest file of rt.jar, which contains information such as its specification and implementation version, vendor, and signature. You can compare this information with the official documentation of your Java version to ensure that you have the correct file.
How to Use rt.jar with Maven
Now that you have downloaded rt.jar, you can use it with Maven by adding it as a dependency in your pom.xml file. However, there are some caveats that you need to be aware of. First, you need to specify the scope of rt.jar as system, which means that it is provided by the JDK/JRE on your machine and is not available in any repository. Second, you need to provide the system path of rt.jar, which is an absolute or relative path to the file on your file system. Third, you need to avoid conflicts with other dependencies that may contain classes from rt.jar, such as javax.* or org.w3c.* packages. To do this, you can either exclude those dependencies or use a different classloader for them.
Here is an example of how to add rt.jar as a dependency in your pom.xml file:
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<dependency> <groupId>rt</groupId> <artifactId> <artifactId>rt</artifactId> <version>1.0</version> <scope>system</scope> <systemPath>$project.basedir/lib/rt.jar</systemPath> </dependency>
This will tell Maven to use the rt.jar file that is located in the lib directory of your project. You can change the system path according to your preference, but make sure that it is valid and accessible. Note that you also need to specify a version for rt.jar, even though it is not a real artifact in any repository. You can use any arbitrary value for the version, as long as it is consistent with your project.
If you have other dependencies that may contain classes from rt.jar, such as javax.* or org.w3c.* packages, you may encounter conflicts or errors during the compilation or runtime of your project. To avoid this, you can either exclude those dependencies from your project, or use a different classloader for them. For example, if you want to exclude everything under src/test/resources/ from the final jar, put this:
<build> <plugins> <!-- configure JAR build --> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>2.3.1</version> <configuration> <excludes> <exclude>src/test/resources/</exclude> </excludes> </configuration> </plugin> </plugins> </build>
This will exclude all the files under src/test/resources/ from the final jar. You can also use wildcards or patterns to exclude specific files or directories. For more information on how to use dependency exclusions, see .
In this article, we have learned how to download and use rt.jar with Maven. We have seen how to find the location of rt.jar in different operating systems and Java versions, how to copy or extract it from the JRE lib directory, and how to verify its integrity and version. We have also learned how to add rt.jar as a dependency in the pom.xml file, how to specify the scope and system path of rt.jar, and how to avoid conflicts with other dependencies that may contain rt.jar classes.
Using rt.jar with Maven can be useful for some scenarios, such as accessing internal or undocumented Java APIs, or using legacy code that depends on rt.jar classes. However, it is not recommended to use rt.jar for general purposes, as it may cause compatibility or security issues, or violate the Java license agreement. Therefore, you should always check if there are alternatives to using rt.jar, such as official Java APIs, third-party libraries, or custom implementations.
We hope that this article has helped you understand how to download and use rt.jar with Maven. If you have any questions or feedback, please feel free to leave a comment below.
What are some alternatives to using rt.jar with Maven?
Some alternatives to using rt.jar with Maven are: - Using official Java APIs that provide similar or equivalent functionality to the classes in rt.jar. For example, instead of using sun.misc.BASE64Encoder/Decoder, you can use java.util.Base64. - Using third-party libraries that offer more features or better performance than the classes in rt.jar. For example, instead of using sun.net.www.http.HttpClient, you can use Apache HttpClient or OkHttp. - Implementing your own classes or methods that mimic or replace the classes in rt.jar. For example, instead of using sun.reflect.Reflection.getCallerClass(), you can use java.lang.StackWalker or java.lang.invoke.MethodHandles.lookup().
How can I update or replace rt.jar in my project?
If you need to update or replace rt.jar in your project, you can follow these steps: - Download the new version of rt.jar from the official Java website or another source. - Copy or extract the new version of rt.jar to your project's lib directory or another location. - Update the system path of rt.jar in your pom.xml file accordingly. - Rebuild your project and test if everything works as expected.
How can I troubleshoot errors related to rt.jar?
If you encounter errors related to rt.jar in your project, you can try these steps - Try these steps to troubleshoot errors related to rt.jar in your project: - Check if you have the correct version of rt.jar that matches your Java version and platform. - Check if you have the correct scope and system path of rt.jar in your pom.xml file. - Check if you have any conflicting dependencies that may contain classes from rt.jar, and exclude them or use a different classloader for them. - Check if you have any security or access restrictions that may prevent Maven from reading or using rt.jar, and adjust them accordingly. - Check if you have any corrupted or missing files or directories that may affect rt.jar, and fix them or restore them from a backup. - Check the Maven logs and stack traces for any clues or error messages related to rt.jar, and search for solutions online or ask for help from experts.
How can I exclude rt.jar classes from my final artifact?
If you want to exclude rt.jar classes from your final artifact, such as a jar or war file, you can use the Maven Shade Plugin. This plugin allows you to create an uber-jar that contains all of your project's dependencies, and also lets you filter out unwanted classes or resources. For example, you can use this configuration in your pom.xml file:
<build> <plugins> <!-- configure uber-jar build --> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-shade-plugin</artifactId> <version>3.2.4</version