自定義classloader的實現

轉自：http://www.blogjava.net/realsmy/archive/2007/04/06/108889.html

 

/** * classloader single * @author zhaojiucheng * @version 1.1 * 新增兩個loadClass的重載方法 * 在1.0的基礎上實現從指定jar包中加載指定的類文件 */ package zhao; import java.io.ByteArrayOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.Enumeration; import java.util.Hashtable; import java.util.List; import java.util.jar.JarEntry; import java.util.jar.JarFile; import java.util.jar.JarInputStream; /** * 自定義類加載器 */ public class MyClassLoader extends ClassLoader { private static String MyClasspath = new String(""); private static ArrayList loadClassList = new ArrayList(); private static Hashtable loadClassHashTable = new Hashtable(); public MyClassLoader() { } /** * 構造自定義的加載器 參數1：路徑名 */ public MyClassLoader(String MyClasspath) { if (!MyClasspath.endsWith("//")) { MyClasspath = MyClasspath + "//"; } this.MyClasspath = MyClasspath; } /** * 設置加載路徑 參數1：路徑名 */ public void SetMyClasspath(String MyClasspath) { if (!MyClasspath.endsWith("//")) { MyClasspath = MyClasspath + "//"; } this.MyClasspath = MyClasspath; } /** * 查找類並加載 參數1：文件名 被 loadClass() 調用 */ public Class findClass(String name) { byte[] classData = null; try { classData = loadClassData(name); } catch (IOException e) { e.printStackTrace(); } Class c = defineClass(name, classData, 0, classData.length); loadClassHashTable.put(name, c); System.out.println("加載" + name + "類成功。"); return c; } /** * 讀取文件字節碼 參數1：文件名 被 findClass() 調用 */ private byte[] loadClassData(String name) throws IOException { String filePath = searchFile(MyClasspath, name + ".class"); System.out.println(filePath); if (!(filePath == null || filePath == "")) { FileInputStream inFile = new FileInputStream(filePath); byte[] classData = new byte[inFile.available()]; inFile.read(classData); inFile.close(); return classData; } System.out.println("讀取字節碼失敗。"); return null; } /** * 加載類 參數1：字節碼數組 參數2：類名 */ public Class loadClass(byte[] classData, String className) throws ClassNotFoundException { Class c = defineClass(className, classData, 0, classData.length); loadClassHashTable.put(className, c); System.out.println("加載" + className + "類成功。"); return c; } /** * 加載類 參數1：類名 */ public Class loadClass(String name) throws ClassNotFoundException { return loadClass(name, false); } /** * 加載類 參數1：類名 參數2：是否分析這個類 */ protected Class loadClass(String name, boolean resolve) throws ClassNotFoundException { byte[] classData = null; Class temp = null; // 如是系統類直接裝載並記錄後返回 if (name.startsWith("java.")) { temp = findSystemClass(name); // 調用父類方法 loadClassHashTable.put(name, temp); System.out.println("loadClass: SystemLoading " + name); return temp; } try { temp = findLoadedClass(name);// here need try again it is how to // work if (temp != null) { System.out.println(name + " have loaded"); return (temp); } try { temp = findClass(name); } catch (Exception fnfe) { } if (temp == null) { temp = findSystemClass(name); } if (resolve && (temp != null)) { resolveClass(temp); } return temp; } catch (Exception e) { throw new ClassNotFoundException(e.toString()); } } /** * 加載類 參數1：要加載的類名 參數2：類所在的jar包名 */ protected Class loadClass(String className, String jarName) throws ClassNotFoundException { String jarPath = searchFile(MyClasspath, jarName + ".jar"); JarInputStream in = null; if (!(jarPath == null || jarPath == "")) { try { in = new JarInputStream(new FileInputStream(jarPath)); JarEntry entry; while ((entry = in.getNextJarEntry()) != null) { // System.out.println(entry.getName()); String outFileName = entry.getName().substring( entry.getName().lastIndexOf("/") + 1, entry.getName().length()); // System.out.println(outFileName); if (outFileName.equals(className + ".class")) { if (entry.getSize() == -1) { System.out.println("錯誤：無法讀取該文件！"); return null; } byte[] classData = new byte[(int) entry.getSize()]; in.read(classData); return loadClass(classData, className); } } } catch (IOException e) { e.printStackTrace(); } finally { try { in.close(); } catch (IOException e) { e.printStackTrace(); } } } else { System.out.println("don't find the " + jarName + ".jar"); return null; } return null; } /** * 查詢文件 參數1：路徑名 參數2：文件名 */ public String searchFile(String classpath, String fileName) { File f = new File(classpath + fileName); // 測試此路徑名錶示的文件是否是一個標準文件 if (f.isFile()) { return f.getPath(); } else { // 返回由此抽象路徑名所表示的目錄中的文件和目錄的名稱所組成字符串數組 String objects[] = new File(classpath).list(); for (int i = 0; i < objects.length; i++) { // 測試此抽象路徑名錶示的文件是否是一個目錄 if (new File(classpath + f.separator + objects[i]) .isDirectory()) { // 迭代遍歷。separator是與系統有關的默認名稱分隔符 return searchFile(classpath + f.separator + objects[i] + f.separator, fileName); } } } System.out.println("沒有找到文件：" + fileName); return null; }; public static void main(String[] args) { MyClassLoader cl = new MyClassLoader("e://test"); try { // 從tools.jar包中加載ContentSigner類 cl.loadClass("ContentSigner", "tools"); } catch (ClassNotFoundException e) { e.printStackTrace(); } } } 

 

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此代碼可以從jar包中提取class