URLClassLoader

URLClassLoader

java.net

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Java 1.2

This ClassLoader provides a useful way to load untrusted Java code from a search path of arbitrary URLs, where each URL represents a directory or JAR file to search. Use the inherited loadClass( ) method to load a named class with a URLClassLoader . Classes loaded by a URLClassLoader have whatever permissions are granted to their java.security. CodeSource by the system java.security.Policy , plus they have one additional permission that allows the class loader to read any resource files associated with the class. If the class is loaded from a local file : URL that represents a directory, the class is given permission to read all files and directories below that directory. If the class is loaded from a local file : URL that represents a JAR file, the class is given permission to read that JAR file. If the class is loaded from a URL that represents a resource on another host, that class is given permission to connect to and accept network connections from that host. Note, however, that loaded classes are not granted this additional permission if the code that created the URLClassLoader in the first place would not have had that permission.

You can obtain a URLClassLoader by calling one of the URLClassLoader( ) constructors or one of the static newInstance( ) methods . If you call newInstance( ) , the loadClass( ) method of the returned URLClassLoader performs an additional check to ensure that the caller has permission to access the specified package.

Figure 12-28. java.net.URLClassLoader

 public class  URLClassLoader  extends java.security.SecureClassLoader {  // Public Constructors  public  URLClassLoader  (URL[ ]  urls  );        public  URLClassLoader  (URL[ ]  urls  , ClassLoader  parent  );      public  URLClassLoader  (URL[ ]  urls  , ClassLoader  parent  ,       URLStreamHandlerFactory  factory  );  // Public Class Methods  public static URLClassLoader  newInstance  (URL[ ]  urls  );        public static URLClassLoader  newInstance  (URL[ ]  urls  , ClassLoader  parent  );  // Public Instance Methods  public URL[ ]  getURLs  ( );  // Protected Methods Overriding SecureClassLoader  protected java.security.PermissionCollection  getPermissions  (java.security.      CodeSource  codesource  );  // Public Methods Overriding ClassLoader  public URL  findResource  (String  name  );        public java.util.Enumeration<URL>  findResources  (String  name  )       throws java.io.IOException;  // Protected Methods Overriding ClassLoader  protected Class<?>  findClass  (String  name  ) throws ClassNotFoundException;  // Protected Instance Methods  protected void  addURL  (URL  url  );        protected Package  definePackage  (String  name  , java.util.jar.Manifest  man  ,       URL  url  ) throws IllegalArgumentException;   }