自定义类加载器

packagecom;

importjava.io.*;
importjava.net.*;
importjava.util.*;
importjava.lang.reflect.Method;

publicclassCustomClassLoaderextendsURLClassLoader{
privateFileInputStreaminput=null;//文件输入流
privateByteArrayOutputStreamout=null;//字节数组输出流
privateString[]url=null;//类文件加载路径
privatebyte[]data=null;//类文件字节码
privateStringextensionalName="";//类文件扩展名

publicCustomClassLoader(URL[]urls)throwsException{
super(urls);
this.url=newString[urls.length];
for(inti=0;i<urls.length;i++){
this.url[i]=urls[i].toURI().toString();
}
}

/*
*解析URL
*/
privatevoidsetFilePath(){
for(inti=0;i<this.url.length;i++){
if(this.url[i].substring(0,4).toLowerCase().equals("file")==true){
this.url[i]=this.url[i].substring(5);
}
}
}

/*
*获得指定类名（包名+类名）文件的字节码
*@namenameString
*@returnbyte[]
*/
privatebyte[]getFileData(Stringname){
try{
this.setFilePath();
for(Stringurl:this.url){
StringfileName=url+name.replace('.','/').concat(".")+
this.getExtensionalName();
input=newFileInputStream(newFile(fileName));
if(input!=null){
break;
}
}

out=newByteArrayOutputStream();
data=newbyte[1024];
intlen=-1;
while((len=input.read(data))!=-1){
out.write(data,0,len);
}
data=out.toByteArray();
}catch(Exceptione){
e.printStackTrace();
}finally{
try{
if(input!=null)
input.close();
if(out!=null)
out.close();
returndata;
}catch(Exceptione){
e.printStackTrace();
returnnull;
}
}
}

/*
*根据指定类名查找类文件
*@paramnameString
*@returnClass
*/
protectedClassfindClassByName(Stringname){
try{
byte[]data=this.getFileData(name);
if(data==null){
returnnull;
}
returnthis.defineClass(name,data,0,data.length);
}catch(Exceptione){
e.printStackTrace();
returnnull;
}

}

/*
*重写loadClass()方法
*@paramnameString
*@returnClass
*/
publicClassloadClass(Stringname){
Classc=null;
try{
c=super.loadClass(name);
}catch(ClassNotFoundExceptione){
e.printStackTrace();
}finally{
if(c==null)//父类默认方法没有加载到指定类时，使用自定义方法查找
c=this.findClassByName(name);
returnc;
}
}

publicStringgetExtensionalName(){
returnextensionalName;
}

publicvoidsetExtensionalName(StringextensionalName){
this.extensionalName=extensionalName;
}



publicstaticvoidmain(String[]args)throwsException{
URL[]url=newURL[]{newURL("file:e:/")};//添加你想要加载类的路径
//网络或本地均可
CustomClassLoadercsl=newCustomClassLoader(url);
csl.setExtensionalName("rs");
Classc1=csl.loadClass("com.demo");
Objectobj=c1.newInstance();
Methodmethod=c1.getMethod("printText",null);
method.invoke(obj,null);
}
}