JavaWeb 多个Servlet整合优化

由于一个Servlet只能接收一个地址的http请求，如果系统复杂度提高，就会有很多Servlet类。例如，对销售系统来说，可能会有OederInsertServlet, OrderUpdateServlet, OrderDeleteSerlvet, OrderQueryServlet等多个OrderServlet来处理订单这一种业务。看着就会很杂。如下图。同时如果请求前或请求后有一些处理的话，对应的方法就需要写很多次，维护难度也会提升

优化-同一个模块多个操作

可以只用一个Servlet接收Order这一种业务所有的接口，通过在接口添加类似operate的标志参数对不同的操作进行区分。

代码示例

protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String operate = req.getParameter("operate");
        if (null == operate){
            doRequireOperate(req, resp);
        }
        SUtils.logInfo("调用前操作");
        System.out.println("获取到的操作名为：" + operate);
        switch (operate){
            case "insert":{
                System.out.println("do insert");
                doInsertOperate(req, resp);
                break;
            }
            case "update":{
                System.out.println("do update");
                doUpdateOperate(req, resp);
                break;
            }
            case "delete":{
                System.out.println("do delete");
                doDeleteOperate(req, resp);
                break;
            }
            case "query":{
                System.out.println("do query");
                doQueryOperate(req, resp);
                break;
            }
            default:{
                System.out.println("error");
            }
            SUtils.logInfo("调用后操作");
        }
    }

测试

本地访问 http://localhost:8080/mvc/ver1?operate=insert

服务器日志输出如下

优化-使用反射

目前，对业务的操作是通过switch-case进行匹配处理的，如果操作数量增多则需要多增加case语句，代码就会显得臃肿。可以考虑通过反射调用具体的执行方法

示例代码

下面展示的是核心代码

String operate = req.getParameter("operate");
System.out.println("获取到的操作名为：" + operate);
        // 通过反射获取对应的方法
        // 假定方法名均为do+${operate}+operate，驼峰，如operate为insert时，要调用的方法就是doInsertOperate
        // Method[] methods = this.getClass().getMethods();
        char[] chars = operate.toCharArray();
        chars[0] -= 32;
        String methodName = "do" + String.valueOf(chars) + "Operate";
        // Optional<Method> targetMethod = Arrays.stream(methods).filter(m -> m.getName().equals(methodName)).findFirst();
        try {
            Method taragetMethod = this.getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            taragetMethod.setAccessible(true);
            taragetMethod.invoke(this, req, resp);
        } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
            throw new RuntimeException(e);
        }

优化-多个业务模块引入配置文件

当业务增多时，需要在每个业务里面单独写反射调用方法较为复杂，可以也通过反射来调用业务模块，再执行对应的方法，同时可以引入xml配置文件，来匹配对应的业务模块

代码示例

@WebServlet("/mvc/ver3/*")
public class Ver3Servlet extends HttpServlet {

    private Map<String, Object> beanControllerMap = new HashMap<>();

    // 初始化，读取xml文件配置controller
    @Override
    public void init() throws ServletException {
        // super.init();
        System.out.println("aaa");
        try (InputStream beanConfigs = this.getClass().getClassLoader().getResourceAsStream("MvcVer3Config.xml")) {
            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            Document beanDocument = documentBuilder.parse(beanConfigs);
            Element documentElement = beanDocument.getDocumentElement();
            NodeList nodeList = beanDocument.getDocumentElement().getElementsByTagName("bean");
            for (int i = 0; i < nodeList.getLength(); i++) {
                if (Node.ELEMENT_NODE == nodeList.item(i).getNodeType()){
                    Element item = (Element) nodeList.item(i);
                    String beanName = item.getAttribute("id");
                    String className = item.getAttribute("class");
                    Class<?> beanClass = Class.forName(className);
                    Object bean = beanClass.getDeclaredConstructors()[0].newInstance();
                    beanControllerMap.put(beanName, bean);
                }
            }
            // documentElement.get
        } catch (IOException | ParserConfigurationException | SAXException | ClassNotFoundException |
                 InvocationTargetException | InstantiationException | IllegalAccessException e) {
            throw new RuntimeException(e);
        }
        System.out.println("aaa");

    }

    // 读取路径值，获取对应的controller对象，反射调用对应方法
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String servletPath = req.getPathInfo();
        System.out.println(servletPath);
        String controllerName = servletPath.split("/")[1];
        String operateName = servletPath.split("/")[2];
        operateName = "do" + getFirstUpper(operateName) + "Operate";
        Object targetController = beanControllerMap.get(getFirstUpper(controllerName));
        Method targetMethod;
        try {
            targetMethod = targetController.getClass().getDeclaredMethod(operateName, HttpServletRequest.class, HttpServletResponse.class);
        } catch (NoSuchMethodException e) {
            ErrorResponse(req, resp, e.getMessage());
            e.printStackTrace();
            return;
        }
        try {
            targetMethod.invoke(targetController, req, resp);
        } catch (IllegalAccessException | InvocationTargetException e) {
            ErrorResponse(req, resp, e.getMessage());
            e.printStackTrace();
            return;
        }
        System.out.println("调用结束");
    }


    private void ErrorResponse(HttpServletRequest req, HttpServletResponse resp, String errorString) throws IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\n");
        out.println("<HTML lang=\"ch\">");
        out.println("  <HEAD><TITLE>delete Servlet</TITLE></HEAD>");
        out.println("  <BODY>");
        out.print("所访问的模块不存在<br>");
        out.print(errorString);
        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
        System.out.println("所访问的模块不存在");
    }

    private String getFirstUpper(String s){
        char[] chars = s.toCharArray();
        chars[0] -= 32;
        return String.valueOf(chars);
    }
}

解决多个业务配置问题，通过读取配置文件初始化Servlet，在收到请求时，取到对应的Servlet进行处理

配置文件示例

<?xml version="1.0" encoding="utf-8" ?>
<beans>
    <bean id="A" class="com.javawebdemo.mvc.controller.AController"/>
    <bean id="B" class="com.javawebdemo.mvc.controller.BController"/>
    <bean id="C" class="com.javawebdemo.mvc.controller.CController"/>
    <bean id="D" class="com.javawebdemo.mvc.controller.DController"/>
</beans>

测试

启动项目，访问对应路径

http://localhost:8080/mvc/ver3/a/query

页面响应

调用成功