What is java library path in linux

java.library.path – What is Java library and how to use

Posted by: Bhagvan Kommadi in Java Basics March 4th, 2014 3 Comments Views

In this tutorial, we will discuss how to set java.library.path. We will explain its definition, and how can be used by Java applications.

The Java Virtual Machine (JVM) uses the java.library.path property in order to locate native libraries. This property is part of the system environment used by Java, in order to locate and load native libraries used by an application.

When a Java application loads a native library using the System.loadLibrary() method, the java.library.path is scanned for the specified library. If the JVM is not able to detect the requested library, it throws an UnsatisfiedLinkError . Finally, the usage of native libraries makes a Java program more platform dependent, as it requires the existence of specific native libraries.

1. What is a java library and why we use it?

A java library consists of software components that are developed by programmers and reusable. They help in providing different services. A java library is in a deployment format called JAR file. The format is based on pkzip file format. A jar file has java classes and resources such as properties, icons, and other files. A java library file can be used in other Java projects by specifying it in the classpath. The classes in the jar file are accessible to java application after the library is specified in the classpath.

2. How to find a library jar and download it?

A java library can be searched in different repositories such as maven, guava, apache-commons, and others. You can download the java library by specifying the version from these repositories. The java library is specified in the classpath and classes from the library are used in java projects. For example, the database driver libraries can be downloaded from the database vendor repositories. Postgres SQL will be available on the PostgreSQL website.

3. How to set the java.library.path property

There are several ways to set the java.library.path property:

Through the command line or terminal: Using the terminal (Linux or Mac) or the command prompt (Windows), we can execute the following command, in order to execute our Java application:

where the path_to_dll argument must be replaced with the path of the required library.

Through Java source code: Inside an application’s code we can set the java.library.path using the following code snippet:

4. Setting the java.library path. using Eclipse

In order to define the java.library.path property in Eclipse , the following steps must be completed:

• Select your project in the Package Explorer area and press a right-click on it.
  1. Select Build Path → Configure Build Path. option.
  2. In the appearing window, select the Libraries tab.
  3. Then, expand the JRE System library option and select the Native library location .
  4. Click on the Edit. button at the right panel.
  5. Locate the required library and then click OK .
  6. Close the window.

If the aforementioned steps have been successfully completed, then the selected project will be executed using the required native library.

5. Setting the java.library path. using Netbeans

In order to define the java.library.path property in Netbeans , the following steps must be completed:

• Select your project in the Projects area and press a right-click on it.
• Select Properties and then, move to the Run tab.
• In the VM Options field, add the following option, based on your library’s path:
  java -Djava.library.path=

Click on OK in order for the window to close.

If the aforementioned steps have been successfully completed, then the selected project will be executed using the required native library.

6. Top 10 Java standard libraries

Top 10 Java standard reusable libraries are mentioned below:

• Core Java Libraries
  • java.lang
  • java.util
  • java.io
  • java.nio
  • java.math
  • java.net
• Java UI Libraries
  • javax.swing
• java.media
• Apache Commons
  • commons.math
  • commons.cli
  • commons.csv
  • commons.io
• spring boot
• google-gson
• hibernate-orm
• Unit Testing Libraries
  • mockito
  • junit
• log4j
• Slf4j

7. Create an example in which you use a library

Let us look at creating a Math Library with public api with methods for product and difference of two integers. MathAPI class is shown as below:

The command used for compilation of the code in the math folder is shown below:

Java library MathAPI.jar is created by using the following command:

The MathAPI library can be used in MathAPIExample as shown below:

The command used for compilation of the code is shown below:

The command used for execution of the code is shown below:

The output of the above command when executed is shown below:

8. Download the Source Code

That was an article about java.library.path: What is Java library and how to use.

Last updated on Oct. 06th, 2020

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How to find path to java?

I needed to update my openJDK to 8 version. And I downloaded the new one this way:

When I check the Java version

But where was it saved? I need to know because I should set this path into AndroidStudio .

4 Answers 4

Simply do (in terminal):

And you’ll get an output like this:

The last line is the place your java is in.

You need to dig into symbolic links. Below is steps to get Java directory

That tells the command java resides in /usr/bin/java.

So, now we know that /usr/bin/java is actually a symbolic link to /etc/alternatives/java .

Dig deeper using the same method above:

So, thats the actual location of java: /usr/local/jre.

You could still dig deeper to find other symbolic links.

To make this seemingly over done setting clearer, on my Ubuntu linux machine with open JDK 8 installed:

but what we need is the path to the directory containing bin of the JDK. So ask for the location of javac and then use dirname twice.

See man update-alternatives for more.

Starting from January 2019, the licensing model for Oracle Java has changed. PPAs such as ‘ppa:webupd8team/java’ used in many Java installation tutorials now become unavailable.

Here I would like to share how I installed Java 8 on Ubuntu 16.04, and set the Java path in terminal.

Installation

I followed the instruction on the official documentation to install Java with .tar.gz

Path setting

The instruction is also from the official documentations. The steps to set up Java path are much simpler here.

After performing all the steps, restart the terminal and run ‘java -version’ to verify installation.

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Where is the java folder for libraries on linux

I need to find \jre\lib\ext under the java folder to add libraries. And I am not sure how to find it

2 Answers 2

Use String extDir = System.getProperty(«java.ext.dirs»); to get the extensions dir path as you want (more info about system properties can be found here), set the path and write the jar files to that directory (be carefull to capture any IOException that could be raise in the writing process because this folders are usually write-protected or require root/admin privileges)

As quoted in the comments, this is something that should only be done in exceptional cases

As most comments say don’t do so, the alternative.

Most applications have an app.jar and a lib folder in which all library jars reside. In the application jar there is a META-INF/MANIFEST.MF with a class path including the lib jars.

As a developer I use maven (like ant, ivy) for the build infra structure and it does it just so. The jars are taken from the local maven repository else from the remote ones. Also maven uses a local repository of all jars in different versions. Jars missing in the remote repositories, like own programming, can be installed there.

BTW /usr/lib/jvm/ contains the java versions (do which java , which javac ).

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How to add .so file to the java.library.path in Linux

I am working with a java application which needs a .dll file in java.library.path in windows. To run same application in Linux I have the respective .so file which should be added to java.library.path in linux machine, I didnt find any easy solution for this so far

I did put the .so in a folder which is already in the class path, but my application still complains there is no required .so file in java.library.path

I’d like to find:

1. Ways to add .so to java.library.path
2. How to know if its already added (when added)

5 Answers 5

Add the containing directory to LD_LIBRARY_PATH before launching the application

Use java -XshowSettings:properties to show the java.library.path (and others) value.

I had a lot of trouble figuring this out, please make sure that you have lib prefix in the library name.

Rename libraries to have lib as a prefix. [Add this as part of build script]

I used java -XshowSettings:properties method and found the path of a previously set folder and copied my so file to that folder

I believe this to be a better way to do it as it only needs one single link to be created, no file edits needed, no exports or running of source before an application is run. And no bashrc lines needed.

That said, if you upgrade it may cause unintentional errors to future java releases as it might load an outdated library, although one link removal also solves this.

This works under ubuntu 18.04 with java 11 opensdk installed.

From the two commands above, you can find the two paths you need to adjust this to your own system.

I made a symlink for java ll open sdk to find the library and mine was as follows because /usr/lib is one of the paths in the output. There is (in my output) a java path you may choose to use instead of /usr/lib if you want to keep java library (even symlinks) together.

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Where can I find the Java SDK in Linux after installing it?

I installed JDK using apt-get install but I don’t know where my jdk folder is. I need to set the path for that. Does any one have a clue on the location?

14 Answers 14

This depends a bit from your package system . if the java command works, you can type readlink -f $(which java) to find the location of the java command. On the OpenSUSE system I’m on now it returns /usr/lib64/jvm/java-1.6.0-openjdk-1.6.0/jre/bin/java (but this is not a system which uses apt-get ).

On Ubuntu, it looks like it is in /usr/lib/jvm/java-6-openjdk/ for OpenJDK, and in some other subdirectory of /usr/lib/jvm/ for Suns JDK (and other implementations as well, I think).

For any given package you can determine what files it installs and where it installs them by querying dpkg. For example for the package ‘openjdk-6-jdk’: dpkg -L openjdk-6-jdk

will tell you which java implementation is the default for your system and where in the filesystem it is installed. Check the manual for more options.

should give you something like

This question will get moved but you can do the following

Use find to located it. It should be under /usr somewhere:

When running the command, if there are too many «Permission denied» message obfuscating the actual found results then, simply redirect stderr to /dev/null

Another best way to find Java folder path is to use alternatives command in Fedora Linux (I know its for Ubuntu but I hit this post from google just by its headline). Just want to share incase people like me looking for answers for fedora flavour.

To display all information regarding java

Three Step Process: First: open Terminal-> $ whereis java it would give output like this: java: /usr/bin/java /usr/share/java /usr/share/man/man1/java.1.gz

Second: ls -l /usr/bin/java It would give output like this: lrwxrwxrwx 1 root root 22 Feb 9 10:59 /usr/bin/java -> /etc/alternatives/java

Third: ls -l /etc/alternatives/java output is the JDK path: lrwxrwxrwx 1 root root 46 Feb 9 10:59 /etc/alternatives/java -> /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java

It’s /usr/local/java/jdk[version]

the command: sudo update-alternatives —config java will find the complete path of all installed Java versions

This question still seems relevant, and the answer seems to be a moving target.

On my debian system (buster):

However, if you actually go look there, you’ll see there are multiple directories and symbolic links placed there by the package system to simplify future maintenance.

The actual directory is java-11-openjdk-amd64 , with another symlink of default-java . There is also an openjdk-11 directory, but it appears to only contain a source.zip file.

Given this, for Debian ONLY, I would guess the best value to use is /usr/lib/jvm/default-java , as this should always be valid, even if you decide to install a totally different version of java, or even switch vendors.

The normal reason to want to know the path is because some application wants it, and you probably don’t want that app to break because you did an upgrade that changed version numbers.

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