java自学day4-JVM核心机制-自定义文件类加载器

自定义文件类加载器

package cn.xqh.reflection;

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

public class FileSystemClassLoader extends java.lang.ClassLoader{
	
	private String rootdir;
	
	public FileSystemClassLoader(String rootdir) {
		this.rootdir=rootdir;
	}
	
	@Override
	protected Class<?> findClass(String name) throws ClassNotFoundException {
		Class c = findLoadedClass(name);
		if(null!=c) {
			return c;
		}else {
			ClassLoader parent = this.getParent();
			try {
				c = parent.loadClass(name);
			} catch (Exception e) {
			
			}
			if(null!=c) {
				return c;
			}else {
				byte[] b =getclassdata(name);
				if(null==b) {
					throw new ClassNotFoundException();
				}else {
					c = defineClass(name, b, 0, b.length);
					return c;
				}
			}
		}
	}
	
	private byte[] getclassdata(String name) {
		String path = rootdir + "/"+ name.replace(".", "/")+".class";
		InputStream is = null;
		ByteArrayOutputStream bos = new ByteArrayOutputStream();		
		
		try {
			is = new FileInputStream(path);
			byte[] car = new byte[1024];
			int temp = 0;
			while((temp=is.read(car))!=-1) {
				bos.write(car, 0, temp);
			}
			return bos.toByteArray();
	
		} catch (Exception e) {
			e.printStackTrace();
			return null;
		}finally {
			if(is!=null) {
				try {
					is.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
		
	}
}



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