Head First Servlet&JSP 3. Mini MVC Tutorial

本章构建并部署一个 MVC web app.

a web application my constant

static content
JSP pages
servlet classes
the deployment descriptor (DD)
tag libraries
JAR files
Java class files

DD 元素的目标和语义

error-page
init-param
mime-mapping
servlet
servlet-class
servlet-mapping
servlet-name
welcome-file

体会一整套的构建过程

development environment
deployment environment
iterative development an testing

POJO (Plain Old Java Object)
Architecture

部署目录不仅要符合 Servlets and JSP specifications，还要慢速 Container-specific rules，且不同的容易规定的部署目录有不同，比如 Tomcat 要求部署到 webapps 目录下。

构建一个 app 的路线图：

reviewed the user views
looked at the architecture
setup the development and deployment environments for creating and deploying the app
creating the app
- Build and test the HTML
- Build and test version 1 (invoked via the HTML form and prints the parameter it receives) of the controller servlet
- Build a test class
- Upgrade the servlet to version 2 (adds the capability of calling the model class to get beer advice)
- Build the JSP, upgrade the servlet to version 3 (which adds the capability of dispatching to the JSP)

书中引入了极限编程（extreme programming）、迭代开发（iterative development）的方法学，and mangle them for out own evil purposes… ; )

开发目录

beerV1
 ├─classes
 │  └─com
 │      └─example
 │          ├─model
 │          └─web
 ├─etc
 │      web.xml
 │
 ├─lib
 ├─src
 │  └─com
 │      └─example
 │          ├─model
 │          │      BeerExpert.java
 │          │
 │          └─web
 │                  BeerSelect.java
 │
 └─web
         form.html
         result.jsp

部署目录（已在 webapps 下）

Beer-v1
 │  form.html
 │  result.jsp
 │
 └─WEB-INF
     │  web.xml
     │
     ├─classes
     │  └─com
     │      └─example
     │          ├─model
     │          └─web
     └─lib

DD web.xml 模板

<?xml version="1.0" encoding="UTF-8"?>  
  
<web-app version="2.5"  
xmlns="http://java.sun.com/xml/ns/javaee"  
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  

</web-app>

URL + <form> 标签的 action 属性 = request URL
eg. /Beer-v1 + /SelectBeer.do = /Beer-v1/SlectBeer.do
".do"不是真的文件后缀，而是一个逻辑名称。

命令行编译遇到的问题：

注：-cp = -classpath

因为 Java 安装在 Program Files 文件夹，空格导致断开，命令行无法识别。

D:\Development\eclipse-workplace\HW>javac -cp %CLASSPATH%;. -d classes src\com\example\web\BeerSelect.javajavac: 无效的标记: Files\Java\jdk1.8.0_192\lib\tools.jar;;.
用法: javac
-help 用于列出可能的选项
处理办法，重命名环境变量，短名称
 处理办法2，用%引用
 处理办法3，创建软连接
 %~d0
how-are-the-digits-after-assigned-in-windows-short-file-names)
how-does-progra1-path-notation-work
wikipedia 8.3_filename
how-to-disable-8-3-file-name-creation-on-ntfs-partitions

最后的解决办法：放到没有空格的路径下。不要自找麻烦。

HttpServlet，setContentType 不要打错成 HttpServer, SelectContentType

package com.example.web;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class BeerSelect extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("Beer Selection Advice<br>");
        String c = request.getParameter("color");
        out.println("<br>Got beer color " + c);
    }
}

# windows
.;D:\Program Files\Java\jdk1.8.0_192\lib\*.jar
# unix
.;D:/Program Files/Java/jdk1.8.0_192/lib/*.jar
# -cp 指定 classpath，这里需要tomcat含有的servlet-api，需要本项目下的classes(？这里仍然有疑问)，需要当前目录., -d 指定编译后的 .class 存放的目录
$javac -cp D:\Development\tomcat\apache-tomcat-8.5.37\lib\servlet-api.jar;classes;. -dclasses src\com\example\web\BeerSelect.java

Model 应该独立。

package com.example.model;
import java.util.*;

public class BeerExpert {
    public List getBrands(String color){
        List brands = new ArrayList();
        if(color.equals("amber")){
            brands.add("Jack Amber");// 警告: [unchecked] 对作为原始类型List的成员的add(E)的调用未经过检查
            brands.add("Red Moose");// 警告: [unchecked] 对作为原始类型List的成员的add(E)的调用未经过检查
        }else{
            brands.add("Jail Pale Ale");// 警告: [unchecked] 对作为原始类型List的成员的add(E)的调用未经过检查
            brands.add("Gout Stout");// 警告: [unchecked] 对作为原始类型List的成员的add(E)的调用未经过检查
        }
        return (brands);
    }
}
//注: src\com\example\model\BeerExpert.java使用了未经检查或不安全的操作。
//注: 有关详细信息, 请使用 -Xlint:unchecked 重新编译。

编译警告的解决办法：类前面加注解：@SuppressWarnings(“unchecked”)

修改 servlet 类

package com.example.web;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*; // List, Iterator
import com.example.model.*;

public class BeerSelect extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("Beer Selection Advice<br>");
        String c = request.getParameter("color");
        // out.println("<br>Got beer color " + new BeerExpert().getBrands(c));
        BeerExpert be = new BeerExpert();
        List result = be.getBrands(c);
        Iterator it = result.iterator();
        while (it.hasNext()) {
            out.print("<br>try: " + it.next());
        }
    }
}

调试的时候要注意清空 Firefox 的缓存，否则 form.html 的改动不会被加载进来。

修改 call JSP

BeerSelect.java

package com.example.web;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*; // List, Iterator
import com.example.model.*;

public class BeerSelect extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        // response.setContentType("text/html");
        // PrintWriter out = response.getWriter();
        // out.println("Beer Selection Advice<br>");
        String c = request.getParameter("color");
        BeerExpert be = new BeerExpert();
        List result = be.getBrands(c);
        
        request.setAttribute("styles",result);
        RequestDispatcher view = request.getRequestDispatcher("result.jsp");
        view.forward(request, response);
    }
}

result.jsp

<%@ page import="java.util.*" %>
<html>

<body>
    <h1 align="center">Beer Recommendations JSP</h1>
    <P>

        <%
        List styles = (List)request.getAttribute("styles");
        Iterator it = styles.iterator();
        while(it.hasNext()){
            out.print("<br>try: "+it.next());
        }
        %>
    </P>
</body>

</html>

至此，相当于第一次打通 B/S 端。
source code

Head First Servlet&JSP 3. Mini MVC Tutorial

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