System load dll java

System load dll java

There are several ways to make it possible for the Java runtime to find and load a dynamic library (DLL) at runtime. I will list them briefly here, followed by examples and further explanation below.

1. Call System.load to load the DLL from an explicitly specified absolute path.
2. Copy the DLL to one of the paths already listed in java.library.path
3. Modify the PATH environment variable to include the directory where the DLL is located.
4. Specify the java.library.path on the command line by using the -D option.
5. If using Eclipse, set the java.library.path in Eclipse for development/debugging.

Note: To help resolve an UnsatisfiedLinkError Runtime Error, see How to Handle the UnsatisfiedLinkError Runtime Error in Java

1. Call System.load to load the DLL from an explicitly specified absolute path.

This choice removes all uncertainty, but embeds a hard-coded path within your Java application. Example:

import com.chilkatsoft.CkZip; public class Test < static < try < System.load("C:/chilkatJava/chilkat.dll"); > catch (UnsatisfiedLinkError e) < System.err.println("Native code library failed to load.\n" + e); System.exit(1); >> public static void main(String argv[]) < CkZip zip = new CkZip(); System.out.println(zip.version()); >>

2. Copy the DLL to one of the paths already listed in java.library.path

To see the current value of the PATH environment variable, open a MS-DOS prompt and type:

Another way of viewing the java.library.path is to run this Java code:

String property = System.getProperty(«java.library.path»); StringTokenizer parser = new StringTokenizer(property, «;»); while (parser.hasMoreTokens())

Note: The java.library.path is initialized from the PATH environment variable. The directories may be listed in a different order, and the current directory «.» should be present in java.library.path, but may not be listed in the PATH environment variable.

The loadLibrary method may be used when the directory containing the DLL is in java.library.path. To load «chilkat.dll», call System.loadLibrary(«chilkat»), as shown here:

import com.chilkatsoft.CkZip; public class Test < static < try < System.loadLibrary("chilkat"); > catch (UnsatisfiedLinkError e) < System.err.println("Native code library failed to load.\n" + e); System.exit(1); >> public static void main(String argv[]) < CkZip zip = new CkZip(); System.out.println(zip.version()); >>

3. Modify the PATH environment variable to include the directory where the DLL is located.

Do this by modifying the PATH environment variable from the Windows Control Panel.

1. Start -> Control Panel -> System -> Advanced
2. Click on Environment Variables, under System Variables, find PATH, and click on it.
3. In the Edit windows, modify PATH by adding the location of the class to the value for PATH. If you do not have the item PATH, you may select to add a new variable and add PATH as the name and the location of the class as the value.
4. Close the window.
5. Reopen Command prompt window, and run your java code.

1. Right click «My Computer» icon
2. Choose «Properties» from context menu
3. Click «Advanced» tab («Advanced system settings» link in Vista)
4. In the Edit windows, modify PATH by adding the location of the class to the value for PATH. If you do not have the item PATH, you may select to add a new variable and add PATH as the name and the location of the class as the value.
5. Reopen Command prompt window, and run your java code.

Important: Setting the PATH environment variable from a MS-DOS command prompt has no effect on java.library.path. For example, this does not work:

set PATH=c:\chilkatJava;%PATH% java Test

Also, modifying the java.library.path from within Java code does not work either:

static < try < // Adding a directory to java.library.path here will not change anything. // System.loadLibrary will still look in the directories listed in java.library.path // as it existed at the very start of the program. // The extra directory path added to java.library.path will not // be searched by loadLibrary. String libpath = System.getProperty("java.library.path"); libpath = libpath + ";C:/chilkatJava"; System.setProperty("java.library.path",libpath); System.loadLibrary("chilkat"); >catch (UnsatisfiedLinkError e) < System.err.println("Native code library failed to load.\n" + e); System.exit(1); >>

4. Specify the java.library.path on the command line by using the -D option.

java -Djava.library.path=c:\chilkatJava TestApp

5. If using Eclipse, set the java.library.path in Eclipse for development/debugging.

1. Open Project->Properties, select «Java Build Path», click on the «Add External JARs. » button and add the «chilkat.jar»
2. (still within the Project Properties dialog) Click on the «Run/Debug Settings», select your Java class, then click on the «Edit. » button. Select the «Arguments» tab, then add -Djava.library.path=»C:\chilkatJava;$» where «C:\chilkatJava» is the directory path containing the «chilkat.dll» file.

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Java System.loadLibrary() – Syntax & Examples

In this tutorial, we will learn about the Java System.loadLibrary() function, and learn how to use this function with the help of examples.

loadLibrary(String libname)

System.loadLibrary(libname) loads the native library specified by the libname argument.

Make sure the library file is present in any of the path specified by java.library.path.

Syntax

The syntax of loadLibrary() function is

loadLibrary(String libname)

Parameter	Description
libname	The name of library.

The function returns void.

Example 1 – loadLibrary(libname)

In this example, we will load a dll present in the Java library path.

awt.dll is present in the location C:\Program Files\Java\jre-10.0.1\bin . And this location is part of java.library.path .

Java Program

Loading Library. Library Loaded.

Example 2 – loadLibrary() – With Extension

In this example, we will provide the extension as well for the library name to loadLibrary() method. loadLibrary() throws java.lang.UnsatisfiedLinkError . So, do not provide the extension in the library name.

Java Program

Loading Library. Exception in thread "main" java.lang.UnsatisfiedLinkError: no awt.dll in java.library.path: [C:\Program Files\Java\jre-10.0.1\bin, C:\WINDOWS\Sun\Java\bin, C:\WINDOWS\system32, ., .] at java.base/java.lang.ClassLoader.loadLibrary(Unknown Source) at java.base/java.lang.Runtime.loadLibrary0(Unknown Source) at java.base/java.lang.System.loadLibrary(Unknown Source) at Example.main(Example.java:5)

Example 3 – loadLibrary(libname) – Null libname

In this example, we will pass null as argument for library name to loadLibrary() method. loadLibrary() throws java.lang.NullPointerException . Make sure that the library name is not null.

Java Program

Loading Library. Exception in thread "main" java.lang.NullPointerException at java.base/java.lang.Runtime.loadLibrary0(Unknown Source) at java.base/java.lang.System.loadLibrary(Unknown Source) at Example.main(Example.java:5)

Example 4 – loadLibrary(libname) – Library not present

In this example, we will try to load a library which is not present anywhere in the Java library paths. In such cases, loadLibrary() throws java.lang.UnsatisfiedLinkError .

Java Program

Loading Library. Exception in thread "main" java.lang.UnsatisfiedLinkError: no nolib in java.library.path: [C:\Program Files\Java\jre-10.0.1\bin, C:\WINDOWS\Sun\Java\bin, C:\WINDOWS\system32, ., .] at java.base/java.lang.ClassLoader.loadLibrary(Unknown Source) at java.base/java.lang.Runtime.loadLibrary0(Unknown Source) at java.base/java.lang.System.loadLibrary(Unknown Source) at Example.main(Example.java:5)

Conclusion

In this Java Tutorial, we have learnt the syntax of Java System.loadLibrary() function, and also learnt how to use this function with the help of examples.

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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.

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