动态加载Jar并实现加载类的对象 [英] Dynamically loading Jar and instanciate an Object of a loaded Class

问题描述

这是类加载器的代码：

  public class ClassLoad {
 
 public static void main（String [] args）{
 
 String filePath = new String（C： /Users/Mehdi/Desktop/JavaClassLoader/jarred.jar）; 
 
 URL myJarFile = null; 
 try {
 myJarFile = new URL（file：//+ filePath）; 
} catch（MalformedURLException e1）{
 System.out.println（1）; 
 e1.printStackTrace（）; 
} 
 
 URLClassLoader cl = URLClassLoader.newInstance（new URL [] {m​​yJarFile}）; 
 
 Class Jarred = null; 
 try {
 Jarred = cl.loadClass（com.jarred.exp.Jarred）; 
} catch（ClassNotFoundException e）{
 System.out.println（2）; 
 e.printStackTrace（）; 
} 
 
方法simpleWrite = null; 
 try {
 simpleWrite = Jarred.getMethod（simpleWrite，new Class [] {String.class}）; 
} catch（SecurityException e）{
 System.out.println（3）; 
 e.printStackTrace（）; 
} catch（NoSuchMethodException e）{
 System.out.println（4）; 
 e.printStackTrace（）; 
} 
 
对象JarredObj = null; 
 try {
 JarredObj = Jarred.newInstance（）; 
} catch（InstantiationException e）{
 System.out.println（5）; 
 e.printStackTrace（）; 
} catch（IllegalAccessException e）{
 System.out.println（6）; 
 e.printStackTrace（）; 
} 
 
 try {
 Object response = simpleWrite.invoke（JarredObj，\Hello Mehdi！It works hamdoulillah：D）; 
} catch（IllegalArgumentException e）{
 e.printStackTrace（）; 
} catch（IllegalAccessException e）{
 e.printStackTrace（）; 
} catch（InvocationTargetException e）{
 e.printStackTrace（）; 
} 
} 
} 
  

和包含的类进入Jar：

  package com.jarred.exp; 
 
 public class Jarred {
 
 public void simpleWrite（String str）{
 System.out.println（str）; 
} 
  

}

它给了我：

  2 
 java.lang.ClassNotFoundException：com.jarred.exp.Jarred 
在java.net.URLClassLoader $ 1.run（未知源）
在java.security.AccessController.doPrivileged（本机方法）
在java.net.URLClassLoader.findClass（未知来源）
在java.lang.ClassLoader.loadClass（未知源）
在java.net.FactoryURLClassLoader.loadClass（未知源）
在java.lang.ClassLoader.loadClass（未知来源）
在ClassLoad。 main（ClassLoad.java:25）
线程main中的异常java.lang.NullPointerException在ClassLoad.main（ClassLoad.java:32）
 
  / pre> 
 
 
你有什么想法吗？谢谢。
解决方案
看起来您的文件网址无效。
 
 
 
 Windows中的文件URI 说
 
 
对于本地Windows文件路径
 
 
 
  C：\Documents and Settings\davris\FileSchemeURIs.doc  
 
 
 
 Windows中相应的有效文件URI ：
 
 
 
  file：/// C：/Documents%20and%20Settings/davris/FileSchemeURIs.doc  
 
 
其中显示冒号后需要  ，而您在
中计算的URL 
 
 
  String filePath = new String（C：/Users/Mehdi/Desktop/JavaClassLoader/jarred.jar）; 
 
 URL myJarFile = null; 
 try {
 myJarFile = new URL（file：//+ filePath）; 
  
在文件之后只有两个斜杠 。可能
  myJarFile = new URL（file：//+ filePath）; 
  
应该是
 code> myJarFile = new URL（file：///+ filePath）; 
  
或者你可以使用  java.io.File.toURI  因此
 文件myJarFile =新文件（C：\\Users\\Mehdi\\Desktop \\JavaClassLoader\\jarred.jar）; 
 if（！myJarFile.isFile（））{
 throw new FileNotFoundException（Missing required JAR：+ myJarFile.toString（））; 
} 
 URL myJarUrl = myJarFile.toURI（）。toURL（）; 
  
具有适当的异常处理。
 
I try to load dynamically a jar into my Java project.

Here's the class loader's code :
public class ClassLoad {

public static void main(String[] args) {

    String filePath = new String("C:/Users/Mehdi/Desktop/JavaClassLoader/jarred.jar");

    URL myJarFile = null;
    try {
        myJarFile = new URL("file://"+filePath);
    } catch (MalformedURLException e1) {
        System.out.println("1");
        e1.printStackTrace();
    }

    URLClassLoader cl = URLClassLoader.newInstance(new URL[]{myJarFile});

    Class Jarred = null;
    try {
        Jarred = cl.loadClass("com.jarred.exp.Jarred");
    } catch (ClassNotFoundException e) {
        System.out.println("2");
        e.printStackTrace();
    }

    Method simpleWrite = null;
    try {
        simpleWrite = Jarred.getMethod("simpleWrite", new Class[] {String.class});
    } catch (SecurityException e) {
        System.out.println("3");
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        System.out.println("4");
        e.printStackTrace();
    }

    Object JarredObj = null;
    try {
        JarredObj = Jarred.newInstance();
    } catch (InstantiationException e) {
        System.out.println("5");
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        System.out.println("6");
        e.printStackTrace();
    }

    try {
        Object response = simpleWrite.invoke(JarredObj, "\nHello Mehdi ! It works hamdoulillah :D");
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    }
}
}
and the Class which is included into the Jar :
package com.jarred.exp;

public class Jarred {

public void simpleWrite(String str) {
    System.out.println(str);
}
}

It gives me : 
2
java.lang.ClassNotFoundException: com.jarred.exp.Jarred
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.net.FactoryURLClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at ClassLoad.main(ClassLoad.java:25)
Exception in thread "main" java.lang.NullPointerException
at ClassLoad.main(ClassLoad.java:32)
Do you have any idea about this ? Thank you.
解决方案
It looks like your file URL is invalid.

"File URIs in Windows" says

  
For the local Windows file path
  
  
C:\Documents and Settings\davris\FileSchemeURIs.doc
  
  
The corresponding valid file URI in Windows is: 
  
  
file:///C:/Documents%20and%20Settings/davris/FileSchemeURIs.doc
which shows that three slashes are needed after the colon, but the URL you are computing in
String filePath = new String("C:/Users/Mehdi/Desktop/JavaClassLoader/jarred.jar");

URL myJarFile = null;
try {
    myJarFile = new URL("file://"+filePath);
has only two slashes after the file:.  Perhaps
    myJarFile = new URL("file://"+filePath);
should be
    myJarFile = new URL("file:///"+filePath);
or alternatively you could use java.io.File.toURI thus
File myJarFile = new File("C:\\Users\\Mehdi\\Desktop\\JavaClassLoader\\jarred.jar");
if (!myJarFile.isFile()) {
  throw new FileNotFoundException("Missing required JAR: " + myJarFile.toString());
}
URL myJarUrl = myJarFile.toURI().toURL();
with appropriate exception handling.

                        
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