动手写web框架(7): 请求转发器

类似于Spring MVC中的DispatcherServlet，所以我们也需要编写一个Servlet，让它处理所有的请求。

1. 从HttpServletRequest对象中获取请求方法和请求路径；
2. 通过ControllerHelper获取Request对应的Handler，Handler包括Controller的类以及处理方法Method；
3. 从HttpServletRequest对象中获取所有参数，封装到一个Param对象中；
4. 通过反射调用Controller实例中对应的Method方法，并获取返回值；
5. 如果返回值是View类型，则返回一个Jsp页面；如果是Data类型，则返回一个JSON数据。

DispatcherServlet

package org.smart4j.framework;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.StringUtils;
import org.smart4j.framework.bean.Data;
import org.smart4j.framework.bean.Handler;
import org.smart4j.framework.bean.Param;
import org.smart4j.framework.bean.View;
import org.smart4j.framework.helper.BeanHelper;
import org.smart4j.framework.helper.ConfigHelper;
import org.smart4j.framework.helper.ControllerHelper;
import org.smart4j.framework.util.CodecUtil;
import org.smart4j.framework.util.JsonUtil;
import org.smart4j.framework.util.ReflectionUtil;
import org.smart4j.framework.util.StreamUtil;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
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.PrintWriter;
import java.lang.reflect.Method;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by Roger on 2016/11/23.
 */
@WebServlet(urlPatterns = "/*", loadOnStartup = 0)
public class DispatcherServlet extends HttpServlet {

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);

        // 初始化Helper类
        HelperLoader.init();

        ServletContext servletContext = config.getServletContext();
        // 注册处理jsp的servlet
        // 传入一个"jsp"参数, 意味着从容器中获取JspServlet(这个Servlet由容器实现, The JSP page compiler and execution servlet)
        ServletRegistration jspServlet = servletContext.getServletRegistration("jsp");
        jspServlet.addMapping(ConfigHelper.getAppJspPath() + "*");

        // 注册处理静态资源的默认servlet
        // 传入一个"default"参数, 意味着从容器中获取DefaultServlet(这个Servlet由容器实现, 它负责处理普通的静态资源响应)
        ServletRegistration defaultServlet = servletContext.getServletRegistration("default");
        defaultServlet.addMapping(ConfigHelper.getAppAssetPath() + "*");
    }

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获取请求方法与请求路径
        String requestMethod = req.getMethod().toLowerCase();
        String requestPath = req.getPathInfo();

        // 获取Action处理器
        Handler handler = ControllerHelper.getHandler(requestMethod, requestPath);
        if (handler != null) {
            // 获取Controller类及其实例
            Class<?> controllerCls = handler.getControllerClass();
            Object controllerBean = BeanHelper.getBean(controllerCls);

            // 创建请求参数对象
            Map<String, Object> paramMap = new HashMap<>();
            Enumeration<String> paramNames = req.getParameterNames();
            while (paramNames.hasMoreElements()){
                String paramName = paramNames.nextElement();
                String paramValue = req.getParameter(paramName);
                paramMap.put(paramName, paramValue);
            }

            String body = CodecUtil.decodeURL(StreamUtil.getString(req.getInputStream()));
            if (StringUtils.isNotEmpty(body)){
                String[] params = StringUtils.split(body, "&");
                if (ArrayUtils.isNotEmpty(params)){
                    for (String param: params){
                        String[] array = StringUtils.split(param, "=");
                        if (ArrayUtils.isNotEmpty(array)){
                            String paramName = array[0];
                            String paramValue = array[1];
                            paramMap.put(paramName, paramValue);
                        }
                    }
                }
            }

            Param param = new Param(paramMap);
            // 调用Action方法
            Method actionMethod = handler.getActionMethod();
            Object result = ReflectionUtil.invokeMethod(controllerBean, actionMethod, param);
            // 处理Action方法返回值
            if (result instanceof View){
                View view = (View) result;
                String path = view.getPath();
                if (StringUtils.isNotEmpty(path)){
                    if (path.startsWith("/")){
                        resp.sendRedirect(req.getContextPath() + path);
                    }else {
                        Map<String, Object> model = view.getModel();
                        for (Map.Entry<String, Object> entry: model.entrySet()){
                            req.setAttribute(entry.getKey(), entry.getValue());
                        }
                        req.getRequestDispatcher(ConfigHelper.getAppJspPath() + path).forward(req, resp);
                    }
                }
            }else if (result instanceof Data){
                // 返回json数据
                Data data = (Data) result;
                Object model = data.getModel();
                if (model != null){
                    resp.setContentType("application/json");
                    resp.setCharacterEncoding("UTF-8");
                    PrintWriter writer = resp.getWriter();
                    writer.write(JsonUtil.toJson(model));
                    writer.flush();
                    writer.close();
                }
            }

        }
    }
}

Param

package org.smart4j.framework.bean;

import org.smart4j.framework.util.CastUtil;

import java.util.Map;

/**
 * 请求参数对象
 * Created by Roger on 2016/11/23.
 */
public class Param {

    private Map<String, Object> paramMap;

    public Param(Map<String, Object> paramMap) {
        this.paramMap = paramMap;
    }

    public long getLong(String name){
        return CastUtil.castLong(paramMap.get(name));
    }

    public int getInt(String name){
        return CastUtil.castInt(paramMap.get(name));
    }

    public double getDouble(String name){
        return CastUtil.castDouble(paramMap.get(name));
    }

    public boolean getBoolean(String name){
        return CastUtil.castBoolean(paramMap.get(name));
    }

    public Map<String, Object> getParamMap() {
        return paramMap;
    }
}

View

package org.smart4j.framework.bean;

import java.util.HashMap;
import java.util.Map;

/**
 * 视图对象
 * Created by Roger on 2016/11/23.
 */
public class View {

    /**
     * 视图路径
     */
    private String path;

    /**
     * 模型数据
     */
    private Map<String, Object> model;

    public View(String path) {
        this.path = path;
        model = new HashMap<>();
    }

    public View addAttr(String key, Object value){
        model.put(key, value);
        return this;
    }

    public String getPath() {
        return path;
    }

    public Map<String, Object> getModel() {
        return model;
    }
}

Data

package org.smart4j.framework.bean;

/**
 * 数据对象
 * Created by Roger on 2016/11/23.
 */
public class Data {

    /**
     * 模型数据
     */
    private Object model;

    public Data(Object model) {
        this.model = model;
    }

    public Object getModel() {
        return model;
    }
}

StreamUtil

package org.smart4j.framework.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

/**
 * 流操作工具集
 * Created by Roger on 2016/11/23.
 */
public final class StreamUtil {

    private static final Logger LOGGER = LoggerFactory.getLogger(StreamUtil.class);

    public static String getString(InputStream is){
        StringBuilder sb = new StringBuilder();
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            String line;
            while ((line = br.readLine()) != null){
                sb.append(line);
            }
        } catch (IOException e) {
            LOGGER.error("get string failure", e);
            throw new RuntimeException(e);
        }
        return sb.toString();
    }
}

CodecUtil

package org.smart4j.framework.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;

/**
 * 编码与解码工具集
 * Created by Roger on 2016/11/23.
 */
public final class CodecUtil {

    private static final Logger LOGGER = LoggerFactory.getLogger(CodecUtil.class);

    /**
     * 将URL编码
     * @param source
     * @return
     */
    public static String encodeURL(String source){
        String target;
        try {
            target = URLEncoder.encode(source, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            LOGGER.error("encode url failure", e);
            throw new RuntimeException(e);
        }
        return target;
    }

    /**
     * 将URL解码
     * @param source
     * @return
     */
    public static String decodeURL(String source){
        String target;
        try {
            target = URLDecoder.decode(source, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            LOGGER.error("decode url failure", e);
            throw new RuntimeException(e);
        }
        return target;
    }
}

JsonUtil

package org.smart4j.framework.util;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;

/**
 * Created by Roger on 2016/11/23.
 */
public final class JsonUtil {

    private static final Logger LOGGER = LoggerFactory.getLogger(JsonUtil.class);

    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

    public static <T> String toJson(T obj){
        String json;
        try {
            json = OBJECT_MAPPER.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            LOGGER.error("convert POJO to JSON failure", e);
            throw new RuntimeException(e);
        }
        return json;
    }

    public static <T> T fromJson(String json, Class<T> type){
        T pojo;
        try {
            pojo = OBJECT_MAPPER.readValue(json, type);
        } catch (IOException e) {
            LOGGER.error("convert JSON to POJO failure", e);
            throw new RuntimeException(e);
        }
        return pojo;
    }
}