我的MVC框架————GothaMVC（3）view层的实现

众所周知现在的前端模板有很多，像JSP，FreeMarker，Velocity等。
面向对象的程序设计要遵守六大设计原则之一的开闭原则，即对扩展开放——对修改关闭。
所以view层的代码，在我这里的核心在于策略模式的实现。
首先，我们写一个view层的接口

package viewTemplate;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import modelWrapper.Model;

public interface IView {

    void viewRender(Model m,HttpServletRequest req,HttpServletResponse resp);
}

然后，依照策略模式，我们需要定义一个“锦囊”来放置各种策略。

package viewTemplate;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import modelWrapper.Model;

public class ViewContext {
    //这里用来放置需要的view
    private IView view;
    //属性注入
    public ViewContext(IView view){
        this.view=view;
    }

    public void render(Model m,HttpServletRequest req,HttpServletResponse resp){
        view.viewRender(m,req, resp);
    }
}

接下来，我们书写JSP的view形式的代码

package viewTemplate;

import java.io.IOException;
import java.util.Set;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import modelWrapper.Model;

public class Jsp implements IView {

    @Override
    public void viewRender(Model model,HttpServletRequest req, HttpServletResponse resp) {

         if(model!=null){
                Set<String> keys=model.getModel().keySet();
                for(String key:keys){
                    req.setAttribute(key, model.getModel().get(key));
                }
            }
            try {
                req.getRequestDispatcher(model.getView()).forward(req, resp);
            } catch (ServletException | IOException e) {
                e.printStackTrace();
            }

    }

}

然后，是FreeMarker和velocity的代码。我懒得去写了，你们自己填空吧，当然也可以自己去扩展IView接口去实现其他你们喜欢的模板，哈哈。

package viewTemplate;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import modelWrapper.Model;

public class FreeMarker implements IView {

    @Override
    public void viewRender(Model m,HttpServletRequest req, HttpServletResponse resp) {

    }

}

package viewTemplate;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import modelWrapper.Model;

public class Velocity implements IView {

    @Override
    public void viewRender(Model m,HttpServletRequest req, HttpServletResponse resp) {

    }

}

最后还没完，我们需要建立一个工厂来维护这些类

package viewTemplate;

public class ViewFactory {
//工厂模式
    public static ViewContext getView(IView view){
        return new ViewContext(view);
    }

    public static Jsp getJsp(){
        return new Jsp();
    }

    public static FreeMarker getFreeMarker(){
        return new FreeMarker();
    }

    public static Velocity getVelocity(){
        return new Velocity();
    }
}