Java System.load() – Syntax & Examples
In this tutorial, we will learn about the Java System.load() function, and learn how to use this function to load a native library into System, with the help of examples.
load(String filename)
System.load() loads the native library specified by the filename argument.
The filename must be an absolute path to the file you would like to load.
Syntax
The syntax of load() function is
Java Program
Loading dll.. Loading finished.
Example 2 – load(String filename) – File Path Incorrect
In this example, we will provide an incorrect path as filename to load() method. load() method should throw java.lang.UnsatisfiedLinkError .
Java Program
Loading dll.. Exception in thread "main" java.lang.UnsatisfiedLinkError: Can't load library: C:\nothing.dll at java.base/java.lang.ClassLoader.loadLibrary(Unknown Source) at java.base/java.lang.Runtime.load0(Unknown Source) at java.base/java.lang.System.load(Unknown Source) at Example.main(Example.java:6)
Example 3 – load(filename) – Null filename
In this example, we will provide a null value as filename to load() method. load() method should throw java.lang.NullPointerException .
Java Program
Loading dll.. Exception in thread "main" java.lang.NullPointerException at java.base/java.io.File.(Unknown Source) at java.base/java.lang.Runtime.load0(Unknown Source) at java.base/java.lang.System.load(Unknown Source) at Example.main(Example.java:6)
Conclusion
In this Java Tutorial, we have learnt the syntax of Java System.load() function, and also learnt how to use this function with the help of examples.
The difference between System.load and System.loadLibrary in Java
sonic0002 2019-02-05 05:49:28 24,158 1
When writing code using native library in Java, normally the first step is loading some native library.
JDK provides two ways to load libraries:
This post will try to explain the differences of these two ways.
According to Java Doc on System.load(), it has below description.
Loads the native library specified by the filename argument. The filename argument must be an absolute path name.
The parameter of this method should be an absolute file path with the extension name.
According to Java Doc on System.loadLibrary(), it has below description:
Loads the native library specified by the libname argument. The libname argument must not contain any platform specific prefix, file extension or path.
The library normally would be loaded from system library path. What is system library path? Let’s take an example, we have below code to load a library.
The exception says it cannot find the library Hello in java.library.path, let’s find out what is the java.library.path?
public static void main(String[] args)
It will print a list of paths in the system. You just need to put the lib under any path printed in the above statement.
Another difference between these is related to dependency between native libraries. Let’s assume there are two native libraries A.dll and B.dll and A.dll is statically linked to B.dll, if using System.load(«D:/A.dll») , it would throw exception even if B.dll is under the same directory as A.dll. In this case, JVM finds that A.ddl depends on B.dll when trying to load A.dll, it will try to find B.dll under java.library.path but B.dll is not found.
There two solutions for this
- Call System.load(«D:/B.dll»), then call System.load(«D:/A.dll»)
- Put A.dll and B.dll under java.library.pat h and then call System.loadLibrary(«A»)
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1 COMMENT
I think that there is minor wrong in «There two solutions for this:». The #2 is wrong. The other needed DLL despite located in java.library.path still errors. The solution, I found is instead to set the PATH environment variable to where the other DLL is. I tested this both in Windows and Linux. It is the PATH that must be set in order that the other DLL is to be found. Else, it is never found even if it is beside. Please rectify.