What is rt.jar and why do you need it?
rt.jar stands for runtime jar and it is a file that contains all of the compiled class files for the base Java Runtime Environment (JRE). It includes the bootstrap classes, which are the run time classes that comprise the Java platform core API. These are essential for running any Java application or applet.
If you are using Java Development Kit (JDK), you will find rt.jar in the jre/lib directory of your JDK installation. If you are using Java Runtime Environment (JRE) only, you will find it in the lib directory of your JRE installation.
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rt.jar contains classes from various packages such as java.lang, java.util, java.io, java.net, java.awt, javax.swing, and many more. These packages provide basic functionality such as strings, collections, input/output, networking, graphics, user interface components, and so on.
In this article, we will show you how to download rt.jar for Java 7, how to use it in your Java projects, and what are some common issues with it and how to fix them.
How to download rt.jar for Java 7?
If you want to use rt.jar for Java 7, you need to download the JDK 7 from the Oracle website. Here are the steps to do so:
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Go to the and scroll down to find Java SE 7.
Select the JDK 7 version that matches your operating system and architecture (e.g. Windows x64, Linux x86, etc.).
Accept the license agreement and click on the download link.
Save the zip file to your computer and extract it to a folder of your choice.
Once you have downloaded and extracted the JDK 7, you can find the rt.jar file in the jre/lib directory of the JDK 7 folder. For example, if you extracted the JDK 7 to C:\jdk1.7.0_80, you will find rt.jar in C:\jdk1.7.0_80\jre\lib.
To use rt.jar in your Java projects, you have two options:
Copy the rt.jar file to your desired location or add it to your classpath.
Add rt.jar as a dependency in your build tool (e.g. Maven, Gradle) or IDE (e.g. Eclipse, IntelliJ IDEA).
How to use rt.jar in your Java projects?
In this section, we will show you how to use rt.jar in your Java projects using both options mentioned above.
Option 1: Copy or add rt.jar to your classpath
If you want to use rt.jar without any build tool or IDE, you can simply copy the rt.jar file to your project folder or any other location that you prefer. Alternatively, you can add rt.jar to your classpath, which is a list of directories and files that Java uses to find classes and resources.
To copy rt.jar to your project folder, you can use the following command in Windows:
copy C:\jdk1.7.0_80\jre\lib\rt.jar C:\myproject\lib
This will copy rt.jar from the JDK 7 folder to the lib folder of your project.
To add rt.jar to your classpath, you can use the following command in Windows:
set CLASSPATH=%CLASSPATH%;C:\jdk1.7.0_80\jre\lib\rt.jar
This will append rt.jar to your existing classpath. You can also use the -cp or -classpath option when running your Java application or applet to specify the classpath.
Option 2: Add rt.jar as a dependency in your build tool or IDE
If you are using a build tool such as Maven or Gradle, or an IDE such as Eclipse or IntelliJ IDEA, you can add rt.jar as a dependency in your project configuration. This will allow you to use the classes from rt.jar without copying or adding it manually.
To add rt.jar as a dependency in Maven, you can use the following snippet in your pom.xml file:
<dependency>
<groupId>com.oracle</groupId>
<artifactId>rt</artifactId>
<version>1.7</version>
<scope>system</scope>
<systemPath>C:\jdk1.7.0_80\jre\lib\rt.jar</systemPath>
</dependency>
This will tell Maven to use rt.jar from the system path specified. Note that you need to use the system scope for this dependency, as it is not available in any public repository.
To add rt.jar as a dependency in Gradle, you can use the following snippet in your build.gradle file:
dependencies
compile files('C:\jdk1.7.0_80\jre\lib\rt.jar')
This will tell Gradle to use rt.jar from the file path specified.
To add rt.jar as a dependency in Eclipse, you can follow these steps:
Right-click on your project and select Properties.
Select Java Build Path and then Libraries.
Click on Add External JARs and browse to C:\jdk1.7.0_80\jre\lib\rt.jar.
Click on OK and then Apply and Close.
This will tell Eclipse to use rt .jar as a library in your project.
To add rt.jar as a dependency in IntelliJ IDEA, you can follow these steps:
Right-click on your project and select Open Module Settings.
Select Modules and then Dependencies.
Click on the + sign and select JARs or directories.
Browse to C:\jdk1.7.0_80\jre\lib\rt.jar and click on OK.
Click on Apply and then OK.
This will tell IntelliJ IDEA to use rt.jar as a library in your project.
What are some common issues with rt.jar and how to fix them?
In this section, we will discuss some common issues that you may encounter when using rt.jar and how to fix them.
Issue 1: Access restriction on class due to restriction on required library rt.jar
If you are using Eclipse, you may see this error message when you try to use a class from rt.jar:
Access restriction: The type 'SomeClass' is not API (restriction on required library 'C:\jdk1.7.0_80\jre\lib\rt.jar')
This means that Eclipse is enforcing some access rules on the classes from rt.jar, which are considered internal and not part of the public API. This is done to prevent accidental use of unsupported or unstable classes that may change or be removed in future versions of Java.
To fix this issue, you have two options:
Change the compiler compliance level to match the JDK version that you are using. For example, if you are using JDK 7, you should set the compiler compliance level to 1.7. This will tell Eclipse to use the same access rules as the JDK.
Disable the access rules for rt.jar in Eclipse. To do this, go to Properties -> Java Build Path -> Libraries -> rt.jar -> Access rules and change the resolution to "Accessible". This will tell Eclipse to ignore the access rules for rt.jar and allow you to use any class from it.
Issue 2: Missing or outdated classes in rt.jar
If you are using an older or different version of JDK than the one that you are targeting, you may find that some classes are missing or outdated in rt.jar. For example, if you are using JDK 6 but targeting Java 8, you may not find some classes that were added or updated in Java 8, such as java.time or java.util.stream.
To fix this issue, you have two options:
Update your JDK version to match the one that you are targeting. For example, if you are targeting Java 8, you should use JDK 8. This will ensure that you have the latest and most compatible version of rt.jar.
Use a different source for rt.jar that matches the one that you are targeting. For example, if you are targeting Java 8, you can use OpenJDK 8, which is an open source implementation of Java 8. You can download OpenJDK 8 from and use its rt.jar instead of the one from Oracle JDK.
Conclusion
In this article, we have learned what rt.jar is and why we need it. We have also shown you how to download rt.jar for Java 7, how to use it in your Java projects, and what are some common issues with it and how to fix them.
Here are some tips and recommendations for using rt.jar:
Use the appropriate version of rt.jar that matches your target Java version and platform.
Avoid using internal or unsupported classes from rt.jar that may cause compatibility or security issues.
Keep your JDK updated to get the latest bug fixes and improvements for rt.jar.
FAQs
What is the difference between rt.jar and classes.jar?
A: classes.jar is the equivalent of rt.jar for MacOSX prior to JDK 7. They both contain the core Java classes.
What is the difference between rt.jar and tools.jar?
A: tools.jar contains additional classes for development tools such as javac, javadoc, and jconsole. It is not required for running Java applications.
What is the difference between rt.jar and jrt-fs.jar?
A: jrt-fs.jar is a jar file that provides access to the JRT file system, which is a new way of storing the Java runtime classes since Java 9. It replaces the rt.jar file.
How can I view the source code of rt.jar?
A: You can use a decompiler tool (e.g. JD-GUI, CFR) to view the source code of the class files in rt.jar. Alternatively, you can download the source code of OpenJDK, which contains most of the classes in rt.jar.
How can I create my own rt.jar?
A: You should not create your own rt.jar, as it may cause compatibility or security issues. However, if you really want to, you can use the jar tool to create a jar file with your own classes and resources.
I hope you have found this article helpful and informative. If you have any questions or feedback, please feel free to leave a comment below. Thank you for reading! 44f88ac181