Load jar file at runtime in java

Load jar file at runtime in java

Solution: your attempt is good what ever you are trying to do can help you by below code I hope this will help you The JVM searches for and loads classes in this order: Bootstrap classes, which are classes that comprise the Java platform, including the classes in rt.jar and several other important JAR files. Solution 2: You will have to open it as zip file, go through the names, assume all entries ending in are class files and load them, ignoring nested classes and such.

How to load classes from jar file at runtime? [duplicate]

your attempt is good what ever you are trying to do can help you by below code

URL urls [] = <>; JarFileLoader cl = new JarFileLoader (urls); cl.addFile ("/opt/mysql-connector-java-5.0.4/mysql-connector-java-5.0.4-bin.jar"); System.out.println ("attempt. "); cl.loadClass ("org.gjt.mm.mysql.Driver"); System.out.println ("Success!"); 

I hope this will help you

The JVM searches for and loads classes in this order:

Bootstrap classes, which are classes that comprise the Java platform, including the classes in rt.jar and several other important JAR files.

Extension classes, which use the Java Extension mechanism. These classes are bundled as JAR files and located in the extensions directory.

User classes are classes that are defined by developers and third parties and that do not take advantage of the extension mechanism.

Java — How to load a class which implements a interface, Each class should be implemented an interface that I define the interfaces and at last, all of classes which implemented by a user, archived in a jar file. Users copy the jar files in to class path and then only give the jar file name to my application. My application should be able to load jar file dynamically.

How to load all classes of a jar file at runtime?

The class loader will load a .class file as soon as it’s needed. If it’s not needed, it won’t be loaded.

Why do you think that your approach will be an improvement over what the class loader already does?

You will have to open it as zip file, go through the names, assume all entries ending in .class are class files and load them, ignoring nested classes and such.

If you really want to read classes dynamically, leave that to the pros, who already implemented that. Implementing your own classloader is hard. Believe me. I already tried a few times. Use something like OSGi instead, which provides you dynamic class loading and much more.

Java — Jar files not running correctly and resources not, 0. You need to provide your map resources where your JAR file can access them. The easiest way to do this is to include them in the JAR file when you build it in Eclipse. The directory structure inside the JAR can be whatever you wish. There is no rule that says «res/» must be before «map/».

How to load a resource from an embedded JAR File

This might be a good resource: http://one-jar.sourceforge.net/version-0.95/

The main idea is that the inner JAR is not loaded by the ClassLoader that loaded the outer JAR automatically, you need to do so manually, e.g. by using a StreamClassLoader to load the inner jar

Only then, from your own ClassLoader you can get that resource using getResourceAsStream(. )

Java — Loading a JAR dynamically from memory, You should use custom ClassLoader and set the JAR file to its classpath. Classes are always loaded lazily, you do not explicitly load them. Once the JAR is on classpath of the ClassLoader, you can resolve resources. Share Improve this answer answered Mar 10, 2015 at 13:12 Crazyjavahacking 8,885 2 …

Loading a JAR dynamically from memory

Since you said “at least list all of the files that exist inside the JAR”, let’s begin with that rather easy task.

Suppose, you have your JarFile in a byte array, byte[] buffer :

try(JarInputStream is=new JarInputStream(new ByteArrayInputStream(buffer))) < for(;;) < JarEntry nextEntry = is.getNextJarEntry(); if(nextEntry==null) break; System.out.println(nextEntry); >> 

Loading classes from such a representation doesn’t work out-of-the-box because the standard ClassLoader implementations rely on the JarFile implementation which relies on a physical file rather than an abstraction.

So unless you simply write the buffer into a temporary file, it boils down to implement your own ClassLoader . Since the JRE supports only stream access as shown above, you will have to scan linearly to find a requested resource/class or iterate once and store the entries into a Map .

One alternative to implementing a ClassLoader is to implement a custom URL handler to use together with a URLClassLoader which reduces the task to the lookup as described above:

final Map map=new HashMap<>(); try(JarInputStream is=new JarInputStream(new ByteArrayInputStream(buffer))) < for(;;) < JarEntry nextEntry = is.getNextJarEntry(); if(nextEntry==null) break; final int est=(int)nextEntry.getSize(); byte[] data=new byte[est>0? est: 1024]; int real=0; for(int r=is.read(data); r>0; r=is.read(data, real, data.length-real)) if(data.length==(real+=r)) data=Arrays.copyOf(data, data.length*2); if(real!=data.length) data=Arrays.copyOf(data, real); map.put("/"+nextEntry.getName(), data); > > URL u=new URL("x-buffer", null, -1, "/", new URLStreamHandler() < protected URLConnection openConnection(URL u) throws IOException < final byte[] data = map.get(u.getFile()); if(data==null) throw new FileNotFoundException(u.getFile()); return new URLConnection(u) < public void connect() throws IOException <>@Override public InputStream getInputStream() throws IOException < return new ByteArrayInputStream(data); >>; > >); try(URLClassLoader cl=new URLClassLoader(new URL[]))

You may have to write the jar to the disk first, then you can use the following to add it to the classpath: (full answer here)

URLClassLoader child = new URLClassLoader (myJar.toURL(), this.getClass().getClassLoader()); Class classToLoad = Class.forName ("com.MyClass", true, child); Method method = classToLoad.getDeclaredMethod ("myMethod"); Object instance = classToLoad.newInstance (); Object result = method.invoke (instance); 

If you want to enumerate the content of a jar that is not in the classpath, you can always treat it as a zip file: (see full answer here)

ZipFile zipFile = new ZipFile("testfile.zip"); Enumeration zipEntries = zipFile.entries(); String fname; while (zipEntries.hasMoreElements())

You should use custom ClassLoader and set the JAR file to its classpath.

Classes are always loaded lazily, you do not explicitly load them. Once the JAR is on classpath of the ClassLoader , you can resolve resources.

Java — How to load classes from jar file at runtime?, The JVM searches for and loads classes in this order: Bootstrap classes, which are classes that comprise the Java platform, including the classes in rt.jar and several other important JAR files. Extension classes, which use the Java Extension mechanism. These classes are bundled as JAR files and located in …

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How to load jar files dynamically at runtime in Java?

Java provides a way to load external libraries, called JAR files, at runtime to extend the functionality of a Java application. This can be useful for a variety of purposes, such as adding new features, integrating with other systems, or updating an application without requiring a full recompilation. However, there are some specific steps that must be taken in order to load JAR files dynamically at runtime.

Method 1: Using the ClassLoader

Using the ClassLoader to Load JAR Files Dynamically at Runtime in Java

You can use the ClassLoader to load JAR files dynamically at runtime in Java. Here are the steps:

URL[] urls = new URL[]  new URL("file:path/to/jar/file.jar") >; ClassLoader cl = new URLClassLoader(urls);

Class loadedClass = cl.loadClass("com.example.MyClass");

Object obj = loadedClass.newInstance(); Method method = loadedClass.getMethod("myMethod"); method.invoke(obj);

Here is an example that puts it all together:

import java.net.URL; import java.net.URLClassLoader; public class Main  public static void main(String[] args) throws Exception  URL[] urls = new URL[]  new URL("file:path/to/jar/file.jar") >; ClassLoader cl = new URLClassLoader(urls); Class loadedClass = cl.loadClass("com.example.MyClass"); Object obj = loadedClass.newInstance(); Method method = loadedClass.getMethod("myMethod"); method.invoke(obj); > >

That’s it! You can now load JAR files dynamically at runtime in Java using the ClassLoader .

Method 2: Using the URLClassLoader

Using the URLClassLoader to Load JAR Files Dynamically at Runtime in Java

You can use the URLClassLoader class to load JAR files dynamically at runtime in Java. This class allows you to load classes and resources from a set of URLs, including JAR files.

Here are the steps to load JAR files dynamically at runtime using the URLClassLoader class:

URL jarUrl = new URL("file:/path/to/your/jar/file.jar");

URLClassLoader classLoader = new URLClassLoader(new URL[]  jarUrl >);

Class?> clazz = classLoader.loadClass("com.example.MyClass");

Object instance = clazz.newInstance(); Method method = clazz.getMethod("myMethod"); method.invoke(instance);

Here’s the complete example code:

import java.net.URL; import java.net.URLClassLoader; import java.lang.reflect.Method; public class Main  public static void main(String[] args) throws Exception  URL jarUrl = new URL("file:/path/to/your/jar/file.jar"); URLClassLoader classLoader = new URLClassLoader(new URL[]  jarUrl >); Class?> clazz = classLoader.loadClass("com.example.MyClass"); Object instance = clazz.newInstance(); Method method = clazz.getMethod("myMethod"); method.invoke(instance); > >

In this example, we assume that the JAR file contains a class named com.example.MyClass with a method named myMethod() . You can replace these with the actual class and method names from your JAR file.

That’s it! With these simple steps, you can load JAR files dynamically at runtime using the URLClassLoader class in Java.

Method 3: Using the ServiceLoader

Here are the steps to load JAR files dynamically at runtime using ServiceLoader in Java:

1. Create an interface that defines the functionality of the JAR files you want to load. For example:

public interface MyPlugin  void doSomething(); >

public class MyPluginImpl implements MyPlugin  public void doSomething()  System.out.println("Hello from MyPluginImpl!"); > >

1. Create a new JAR file and include the interface and implementation JAR files. This new JAR file will be the one that is dynamically loaded at runtime.
2. In your main application, use the ServiceLoader class to load the JAR file and get an instance of the implementation. For example:

ServiceLoaderMyPlugin> loader = ServiceLoader.load(MyPlugin.class); for (MyPlugin plugin : loader)  plugin.doSomething(); >

This code will load all implementations of the MyPlugin interface that are available in the classpath and call the doSomething() method on each of them.

1. To run the code, make sure that the JAR files containing the interface and implementation are in the classpath. You can add them to the classpath using the -cp command line option or by setting the CLASSPATH environment variable.

That’s it! With these steps, you can dynamically load JAR files at runtime using ServiceLoader in Java.

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