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从零写一个具有IOC-AOP-MVC功能的框架---学习笔记---10. MVC 结果渲染器的编写

1. 本章需要完成的内容

完成请求处理器接口RequestProcessor的编写
完成ResultRender渲染器接口的编写
完成DefultResultRender默认渲染器类的编写
完成InternalErrorResultRender内部异常渲染器类的编写
完成JsonResultRender Json渲染器类的编写
完成ResourceNotFoundResultRender 资源未找到时使用的渲染器类编写
完成ViewResultRender 页面渲染器类的编写
完成DispatcherServlet http请求拦截器的编写
完成RequestProcessorChain 责任链类的编写

2. 第一部分内容

该部分完成DispatcherServlet与RequestProcessorChain类的编写

2.1 DispatcherServlet类

2.1.1 需要完成的代码如下：

package com.wuyiccc.helloframework.mvc;

import com.wuyiccc.helloframework.aop.AspectWeaver;
import com.wuyiccc.helloframework.core.BeanContainer;
import com.wuyiccc.helloframework.injection.DependencyInjector;
import com.wuyiccc.helloframework.mvc.processor.RequestProcessor;
import com.wuyiccc.helloframework.mvc.processor.impl.ControllerRequestProcessor;
import com.wuyiccc.helloframework.mvc.processor.impl.JspRequestProcessor;
import com.wuyiccc.helloframework.mvc.processor.impl.PreRequestProcessor;
import com.wuyiccc.helloframework.mvc.processor.impl.StaticResourceRequestProcessor;
import lombok.extern.slf4j.Slf4j;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

/**
 * @author wuyiccc
 * @date 2020/7/14 21:42
 * 岂曰无衣，与子同袍~
 */
@WebServlet("/*")
@Slf4j
public class DispatcherServlet extends HttpServlet {

    private static final String HELLOFRAMEWORK_CONFIG_FILE = "config/helloframework-config.properties";


    private List<RequestProcessor> PROCESSOR = new ArrayList<>();

    @Override
    public void init() throws ServletException {

        // 1. 初始化容器
        BeanContainer beanContainer = BeanContainer.getInstance();

        beanContainer.loadBeans(getHelloFrameworkScanPackages());
        new AspectWeaver().doAop();
        new DependencyInjector().doIoc();
        // 2. 初始化请求处理器责任链
        PROCESSOR.add(new PreRequestProcessor());
        PROCESSOR.add(new StaticResourceRequestProcessor(getServletContext()));
        PROCESSOR.add(new JspRequestProcessor(getServletContext()));
        PROCESSOR.add(new ControllerRequestProcessor());
    }

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1. 创建责任链对象实例
        RequestProcessorChain requestProcessorChain = new RequestProcessorChain(PROCESSOR.iterator(), req, resp);
        // 2. 通过责任链模式来依次调用请求处理器对请求进行处理
        requestProcessorChain.doRequestProcessorChain();
        // 3. 对处理结果进行渲染
        requestProcessorChain.doRender();
    }

    private String getHelloFrameworkScanPackages() {
        Properties properties = new Properties();
        InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(HELLOFRAMEWORK_CONFIG_FILE);
        try {
            properties.load(in);
        } catch (IOException e) {
            log.warn("The config/helloframework.properties can not load");
            e.printStackTrace();
        }

        String scanPackages = properties.getProperty("helloframework.scan.packages");
        log.info("this is scanPackages: {}", scanPackages);
        return scanPackages;
    }
}

2.1.2 DIspatcherServlet类相关代码讲解：

从零写一个具有IOC-AOP-MVC功能的框架---学习笔记---10. MVC 结果渲染器的编写

2.2 RequestProcessorChain类

2.2.1 需要完成的代码如下:

package org.myframework.mvc;

/**
 * @author wuyiccc
 * @date 2020/6/16 18:48
 * 岂曰无衣，与子同袍~
 */

import lombok.Data;
import lombok.extern.slf4j.Slf4j;
import org.myframework.mvc.processor.RequestProcessor;
import org.myframework.mvc.render.DefaultResultRender;
import org.myframework.mvc.render.InternalErrorResultRender;
import org.myframework.mvc.render.ResultRender;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Iterator;

/**
 * 1. 以责任链的模式执行注册的请求处理器
 * 2. 委派给特定的Render实例对处理后的结果进行渲染
 */
@Data
@Slf4j
public class RequestProcessorChain {

    // 请求处理器迭代器
    private Iterator<RequestProcessor> requestProcessorIterator;

    private HttpServletRequest request;

    private HttpServletResponse response;

    // http请求方法
    private String requestMethod;

    // http请求路径
    private String requestPath;

    // http响应状态码
    private int responseCode;

    // 请求结果渲染器
    private ResultRender resultRender;


    public RequestProcessorChain(Iterator<RequestProcessor> requestProcessorIterator, HttpServletRequest request, HttpServletResponse response) {
        this.requestProcessorIterator = requestProcessorIterator;
        this.request = request;
        this.response = response;
        this.requestMethod = request.getMethod();
        this.requestPath = request.getPathInfo();
        this.responseCode = HttpServletResponse.SC_OK;
    }

    /**
     * 以责任链的模式执行请求链
     */
    public void doRequestProcessorChain() {
        // 1. 通过迭代器遍历注册的请求处理器实现类列表
        try {
            while (requestProcessorIterator.hasNext()) {
                // 2. 知道某个请求处理器执行后返回为false为止
                if (!requestProcessorIterator.next().process(this)) {
                    break;
                }
            }
        } catch (Exception e) {
            // 3. 期间如果出现异常，则交给内部异常渲染器处理
            this.resultRender = new InternalErrorResultRender(e.getMessage());
            log.error("doRequestProcessorChain error: ", e);
        }

    }


    /**
     * 执行处理器
     */
    public void doRender() {
        // 1. 如果请求处理器实现类均未选择合适的渲染器，则使用默认的
        if (this.resultRender == null) {
            this.resultRender = new DefaultResultRender();
        }
        // 2. 调用渲染器的render方法对结果进行渲染
        try {
            this.resultRender.render(this);
        } catch (Exception e) {
            log.error("doRender error: ", e);
            throw new RuntimeException(e);
        }

    }
}

从零写一个具有IOC-AOP-MVC功能的框架---学习笔记---10. MVC 结果渲染器的编写