接續上一篇文章自定義Java web框架(五)
本章主要講解請求轉發到後端之後如何處理的請求轉發，也叫路由。
實現思路如下：
我們需要編寫一個Servlet，讓它來處理所有的請求，從HttpServletRequest物件中獲取請求方法與請求路徑，通過ControllerHelper#getHandler方法來獲取Handler物件。當拿到這個Handler物件之後，可以獲取Controller的類，進而通過BeanHelper來獲取Controller例項物件，然後獲取Action方法，返回View物件或者是Json資料。
首先，封裝請求引數物件如下：

public class Param {

    private Map<String, Object> paramMap;

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

    /**
     * 根據引數名獲取 long 型引數值
     * @param name
     * @return
     */
    public long getLong(String name) {
        return CastUtil.castLong(paramMap.get(name));
    }

    /**
     * 獲取所有欄位資訊
     * @return
     */
    public Map<String, Object> getMap() {
        return paramMap;
    }
}
 

然後，封裝返回檢視資料如下：

public class View {

    /**
     * 檢視路徑
     */
    private String path;

    /**
     * 模型資料
     */
    private Map<String, Object> model;

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

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

    public String getPath() {
        return path;
    }

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

封裝返回JSON資料如下：

public class Data {

    private Object model;

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

    public Object getModel() {
        return model;
    }
}

核心請求轉發器類如下：

public class DispatcherServlet extends HttpServlet {

    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        //初始化相關 Helper類
        HelperLoader.init();
        //獲取ServletContext物件(用於註冊Servlet)
        ServletContext servletContext = servletConfig.getServletContext();
        //註冊處理JSP的Servlet
        ServletRegistration jspServlet = servletContext.getServletRegistration("jsp");
        jspServlet.addMapping(ConfigHelper.getAppJspPath() + "*");
        //註冊處理靜態資源的預設servlet
        ServletRegistration defaultServlet = servletContext.getServletRegistration("default");
        defaultServlet.addMapping(ConfigHelper.getAppAssetPath() + "*");
    }

    @Override
    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //獲取請求方法與請求路徑
        String requestMethod = request.getMethod().toLowerCase();
        String requestPath = request.getPathInfo();
        //獲取Action處理器
        Handler handler = ControllerHelper.getHandler(requestMethod, requestPath);
        if (handler != null) {
            //獲取 Controller 類及其 Bean例項
            Class<?> controllerClass = handler.getControllerClass();
            Object controllerBean = BeanHelper.getBean(controllerClass);
            // 建立請求引數物件
            Map<String, Object> paramMap = new HashMap<>();
            Enumeration<String> paramNames = request.getParameterNames();
            while (paramNames.hasMoreElements()) {
                String paramName = paramNames.nextElement();
                String paramValue = request.getParameter(paramName);
                paramMap.put(paramName, paramValue);
            }
            String body = CodecUtil.decodeURL(StreamUtil.getString(request.getInputStream()));
            if (StringUtils.isNotEmpty(body)) {
                String[] params = StringUtils.split(body, "&");
                if (ArrayUtil.isNotEmpty(params)) {
                    for (String param : params) {
                        String[] array =StringUtils.split(param, "=");
                        if (ArrayUtil.isNotEmpty(array) && array.length == 2) {
                            String paramName = array[0];
                            String paramValue = array[1];
                            paramMap.put(paramName, paramValue);
                        }
                    }
                }
            }

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

}
 

相關的工具類如下：

public class CastUtil {


    /**
     * 轉為long型別
     * @param obj
     * @return
     */
    public static long castLong(Object obj){
        return CastUtil.castLong(obj,0);
    }

    /**
     * 轉為long
     * @param obj
     * @param defaultValue
     * @return
     */
    public static long castLong(Object obj,long defaultValue){
        long value = defaultValue;
        if (obj!=null){
            String strValue = castString(obj);
            if (StringUtils.isNotEmpty(strValue)){
                try{
                    value = Long.parseLong(strValue);
                }catch (NumberFormatException e){
                    value = defaultValue;
                }
            }
        }
        return value;
    }

    /**
     * 轉為String
     * @param obj
     * @return
     */
    public static String castString(Object obj){
        return CastUtil.castString(obj,"");
    }

    /**
     * 轉為String
     * @param obj
     * @param defaultValue
     * @return
     */
    public static String castString(Object obj,String defaultValue){
        return obj!=null?String.valueOf(obj):defaultValue;
    }


}

public final class CodecUtil {

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

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

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

public class StreamUtil {

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

    /**
     * 從輸入流中獲取字串
     * @param inputStream
     * @return
     */
    public static String getString(InputStream inputStream) {
        StringBuilder sb = new StringBuilder();
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
        } catch (Exception e) {
            LOGGER.error("get String failure", e);
            throw new RuntimeException(e);
        }
        return sb.toString();
    }
}

到這裡簡單的MVC框架已經完成，接下來需要寫些簡單的業務功能程式碼，進一步熟悉下整個處理流程。
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