原文地址:http://www.cnblogs.com/cping1982/archive/2007/11/12/2258094.html
我們大家都知道,每個運行中的線程都有一個成員contextClassLoader,用來在運行時動態地載入其它類。
系統默認的contextClassLoader是systemClassLoader,所以一般而言java程序在執行時可以使用JVM自帶的類、$JAVA_HOME/jre/lib/ext/中的類和$CLASSPATH/中的類,對於非默認的jar,一般只能手動在配置環境添加。
但事實上,我們可以通過Thread.currentThread().setContextClassLoader()更改當前線程的contextClassLoader行爲,實現在程序內加載外部jar。
PS:
ClassLoader的工作原理是:
1) 線程需要用到某個類時,contextClassLoader將被請求來載入該類
2) contextClassLoader請求它的父ClassLoader來完成該載入請求
3) 如果父ClassLoader無法載入類,則contextClassLoader試圖自己來載入
package org.loon.framework.jar;
/**
* <p>Title: LoonFramework</p>
* <p>Description:JarLoader,用於jar包的外部操作</p>
* <p>Copyright: Copyright (c) 2007</p>
* <p>Company: LoonFramework</p>
* @author chenpeng
* @email:[email protected]
* @version 0.1
*/
import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;
import java.util.jar.Manifest;
public class JarLoader extends ClassLoader {
//資源緩存
public static Hashtable resources = new Hashtable();
public static JarLoader loader = new JarLoader();
public static Class load(byte[] resource) throws Exception {
// 主函數所在類全稱
String mainClassName = "";
//class資源及實體緩存
ArrayList classNames = new ArrayList();
ArrayList classBuffers = new ArrayList();
// 存儲依賴類
HashMap depends = new HashMap();
// 將byte[]轉爲JarInputStream
JarInputStream jar = new JarInputStream(new ByteArrayInputStream(
resource));
Manifest manifest = jar.getManifest();
// 當Main-Class被聲明時,獲得主函數所在類全稱
if (manifest != null) {
mainClassName = manifest.getMainAttributes().getValue("Main-Class");
}
// 依次獲得對應JAR文件中封裝的各個被壓縮文件的JarEntry
JarEntry entry;
while ((entry = jar.getNextJarEntry()) != null) {
// 當找到的entry爲class時
if (entry.getName().toLowerCase().endsWith(".class")) {
// 將類路徑轉變爲類全稱
String name = entry.getName().substring(0,
entry.getName().length() - ".class".length()).replace(
'/', '.');
// 加載該類
byte[] data = getResourceData(jar);
// 緩存類名及數據
classNames.add(name);
classBuffers.add(data);
} else {
// 非class結尾但開頭字符爲'/'時
if (entry.getName().charAt(0) == '/') {
resources.put(entry.getName(), getResourceData(jar));
// 否則追加'/'後緩存
} else {
resources.put("/" + entry.getName(), getResourceData(jar));
}
}
}
//當獲得的main-class名不爲空時
while (classNames.size() > 0) {
//獲得類路徑全長
int n = classNames.size();
for (int i = classNames.size() - 1; i >= 0; i--) {
try {
//查詢指定類
loader.defineClass((String) classNames.get(i),
(byte[]) classBuffers.get(i), 0,
((byte[]) classBuffers.get(i)).length);
//獲得類名
String pkName = (String) classNames.get(i);
if (pkName.lastIndexOf('.') >= 0) {
pkName = pkName
.substring(0, pkName.lastIndexOf('.'));
if (loader.getPackage(pkName) == null) {
loader.definePackage(pkName, null, null, null,
null, null, null, null);
}
}
//查詢後刪除緩衝
classNames.remove(i);
classBuffers.remove(i);
} catch (NoClassDefFoundError e) {
depends.put((String) classNames.get(i), e.getMessage()
.replaceAll("/", "."));
} catch (UnsupportedClassVersionError e) {
//jre版本錯誤提示
throw new UnsupportedClassVersionError(classNames.get(i)
+ ", " + System.getProperty("java.vm.name") + " "
+ System.getProperty("java.vm.version") + ")");
}
}
if (n == classNames.size()) {
for (int i = 0; i < classNames.size(); i++) {
System.err.println("NoClassDefFoundError:"
+ classNames.get(i));
String className = (String) classNames.get(i);
while (depends.containsKey(className)) {
className = (String) depends.get(className);
}
}
break;
}
}
try {
//加載
Thread.currentThread().setContextClassLoader(loader);
// 獲得指定類,查找其他類方式相仿
return Class.forName(mainClassName, true, loader);
} catch (ClassNotFoundException e) {
String className = mainClassName;
while (depends.containsKey(className)) {
className = (String) depends.get(className);
}
throw new ClassNotFoundException(className);
}
}
/**
* 獲得指定路徑文件的byte[]形式
* @param name
* @return
*/
final static public byte[] getDataSource(String name) {
FileInputStream fileInput;
try {
fileInput = new FileInputStream(new File(name));
} catch (FileNotFoundException e) {
fileInput = null;
}
BufferedInputStream bufferedInput = new BufferedInputStream(fileInput);
return getDataSource(bufferedInput);
}
/**
* 獲得指定InputStream的byte[]形式
* @param name
* @return
*/
final static public byte[] getDataSource(InputStream is) {
if (is == null) {
return null;
}
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
byte[] arrayByte = null;
try {
byte[] bytes = new byte[8192];
bytes = new byte[is.available()];
int read;
while ((read = is.read(bytes)) >= 0) {
byteArrayOutputStream.write(bytes, 0, read);
}
arrayByte = byteArrayOutputStream.toByteArray();
} catch (IOException e) {
return null;
} finally {
try {
if (byteArrayOutputStream != null) {
byteArrayOutputStream.close();
byteArrayOutputStream = null;
}
if (is != null) {
is.close();
is = null;
}
} catch (IOException e) {
}
}
return arrayByte;
}
/**
* 獲得指定JarInputStream的byte[]形式
* @param jar
* @return
* @throws IOException
*/
final static private byte[] getResourceData(JarInputStream jar)
throws IOException {
ByteArrayOutputStream data = new ByteArrayOutputStream();
byte[] buffer = new byte[8192];
int size;
while (jar.available() > 0) {
size = jar.read(buffer);
if (size > 0) {
data.write(buffer, 0, size);
}
}
return data.toByteArray();
}
/**
* 重載的getResource,檢查是否重複包含
*/
public URL getResource(String name) {
if (resources.containsKey("/" + name)) {
try {
return new URL("file:///" + name);
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
return super.getResource(name);
}
/**
* 執行指定class類
* @param clz
* @param methodName
* @param args
*/
public static void callVoidMethod(Class clz, String methodName,
String[] args) {
Class[] arg = new Class[1];
arg[0] = args.getClass();
try {
Method method = clz.getMethod(methodName, arg);
Object[] inArg = new Object[1];
inArg[0] = args;
method.invoke(clz, inArg);
} catch (Exception e) {
System.err.println(e.getMessage());
}
}
/**
* 重載的getResourceAsStream,檢查是否重複包含
*/
public InputStream getResourceAsStream(String name) {
if (name.charAt(0) == '/') {
name = name.substring(1);
}
if (resources.containsKey("/" + name)) {
return new ByteArrayInputStream((byte[]) resources.get("/" + name));
}
return super.getResourceAsStream(name);
}
}
運行示例:
public class JarTest {
public static void main(String[] args) {
//將jar包轉爲byte[]
byte[] resource = JarLoader.getDataSource("D:/fps_test.jar");
try {
//通過byte[]獲得主函數所在類
Class clz = JarLoader.load(resource);
//調用main函數
JarLoader.callVoidMethod(clz, "main", new String[] {""});
} catch (Exception e) {
e.getStackTrace();
}
}
}