04-------Servlet适配器设计模式解决代码丑陋之GenericServlet

超、凢脫俗 2021-11-09 15:26 224阅读 0赞

[适配器模式][Link 1]

**1、目前编写的Java Servlet类实现javax.servlet.Servlet接口。但是Servlet接口中大部分情况下都是在编写service方法，其它方法可能很少用，每一次都把所有的方法全部实现，代码丑陋，可以使用适配器设计模式解决这个问题。**

**2、提供一个抽象类GenericServlet【标准通用的Servlet】，该类作为Servlet接口的适配器，以后编写Servlet类不再直接实现Servlet接口了，继承GenericServlet即可。重点实现service方法。**

**3、GenericServlet适配器将来会被Java Servlet类继承，方便子类的使用。编写Java Servlet继承GenericServlet，只重写(实现)service方法。**

**GenericServlet文档如下：**

public abstract class GenericServlet
    extends Object
    implements Servlet, ServletConfig, Serializable
    Defines a generic, protocol-independent servlet. To write an HTTP servlet for use on the Web, extend HttpServlet instead.
    
    GenericServlet implements the Servlet and ServletConfig interfaces. GenericServlet may be directly extended by a servlet, although it's more common to extend a protocol-specific subclass such as HttpServlet.
    
    GenericServlet makes writing servlets easier. It provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface. GenericServlet also implements the log method, declared in the ServletContext interface.
    
    To write a generic servlet, you need only override the abstract service method.

**简写一个GenericServlet：**

import java.io.IOException;
    import java.util.Enumeration;
    
    import javax.servlet.Servlet;
    import javax.servlet.ServletConfig;
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    //适配器
    public abstract class GenericServlet implements Servlet {
    
    	private ServletConfig config;
    	
    	@Override
    	public final void init(ServletConfig config) throws ServletException {
    		this.config = config;
    		this.init();
    	}
    
    	//子类应该重写的函数
    	public void init() {
    	}
    
    	@Override
    	public ServletConfig getServletConfig() {
    		return config;
    	}
    
    	@Override
    	public abstract void service(ServletRequest req, ServletResponse res)
    			throws ServletException, IOException;
    
    	@Override
    	public String getServletInfo() {
    		return "";
    	}
    
    	@Override
    	public void destroy() {
    	}
    	
    	//改造的时候可以额外再添加一些函数，以供子类使用。
    	public ServletContext getServletContext(){
    		return getServletConfig().getServletContext();
    	}
    	
    	public Enumeration<String> getInitParameterNames(){
    		return getServletConfig().getInitParameterNames();
    	}
    	
    	public String getInitParameter(String name){
    		return getServletConfig().getInitParameter(name);
    	}
    	
    	//................
    	
    
    }

编写Java Servlet都继承GenericServlet：

import java.io.IOException;
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    
    public class HelloServlet extends javax.servlet.GenericServlet {
    
    	@Override
    	public void service(ServletRequest request, ServletResponse response)
    			throws ServletException, IOException {
    		response.setContentType("text/html;charset=UTF-8");
    		ServletContext application = this.getServletContext();
    		response.getWriter().print("Hello Servlet!<br>application=" + application);
    	}
    }

**希望对你有帮助，祝你有一个好心情，加油！**

**若有错误、不全、可优化的点，欢迎纠正与补充！**

[Link 1]: https://blog.csdn.net/cheng_feng_xiao_zhan/article/details/103892113