三种实现servlet的方式有什么区别？--转载

package javax.servlet;

import java.io.IOException;


public interface Servlet {

    public void init(ServletConfig config) throws ServletException;
    
    public ServletConfig getServletConfig();
    

    public void service(ServletRequest req, ServletResponse res)
	throws ServletException, IOException;
	
    public String getServletInfo();
    

    public void destroy();
}

package javax.servlet;

import java.io.IOException;
import java.util.Enumeration;
import java.util.ResourceBundle;

public abstract class GenericServlet 
    implements Servlet, ServletConfig, java.io.Serializable
{
    private static final String LSTRING_FILE = "javax.servlet.LocalStrings";
    private static ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);

    private transient ServletConfig config;
    

    public GenericServlet() { }
    
    
    public void destroy() {
    }
    
    
    public String getInitParameter(String name) {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getInitParameter(name);
    }
    
    
    public Enumeration<String> getInitParameterNames() {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getInitParameterNames();
    }   
     
   
    public ServletConfig getServletConfig() {
	return config;
    }
 
    public ServletContext getServletContext() {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getServletContext();
    }

    public String getServletInfo() {
	return "";
    }


    public void init(ServletConfig config) throws ServletException {
	this.config = config;
	this.init();
    }


    public void init() throws ServletException {

    }
    

      
    public void log(String msg) {
	getServletContext().log(getServletName() + ": "+ msg);
    }
   

    public void log(String message, Throwable t) {
	getServletContext().log(getServletName() + ": " + message, t);
    }
    
    public abstract void service(ServletRequest req, ServletResponse res)
	throws ServletException, IOException;
    
    public String getServletName() {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getServletName();
    }
}