Javaweb finishing notes

Paging

• MySQL uses:

limit 起始条数,显示多少条

• Oracle uses:

SELECT * FROM(
       SELECT e.*,ROWNUM rn FROM emp e
       WHERE ROWNUM <=20
)WHERE rn>10;
-- 第10条开始，取10条

• Tab object encapsulates

public class Page<T> {
    private List<T> datas = new ArrayList<T>();// 数据

    private int size;// 显示条数:10
    private int dataCount;// 总120条
    private int pre;// 上一页
    private int now;// 第3页:
    private int count;// 共5页/尾页
    private int next;// 下一页
    private int start;// 显示页码开始
    private int end;// 显示页码结束
    private String url;// 路径
    // 共130条/第3页/共5页
    // 第一页 上一页 [1][2]3[4][5] 下一页 尾页

    /**
     * @param size
     */
    public Page(int size, int dataCount, int nowPage) {
        // 根据数据总条数来计算总页数:count/size如果除不尽则加1
        this.size = size;
        this.dataCount = dataCount;

        if (this.dataCount % this.size == 0) {
            this.count = this.dataCount / this.size;
        } else {
            this.count = (this.dataCount / this.size) + 1;
        }

        if (nowPage <= 0) {
            this.now = 1;
            this.pre = 1;
            this.next = this.now + 1;
        } else if (nowPage >= this.count) {
            this.now = this.count;
            this.pre = this.now - 1;
            this.next = this.count;
        } else {
            this.now = nowPage;
            this.pre = 1;
            this.next = this.now + 1;
        }
        // 显示页码计算
        this.start = this.now - 5;
        this.end = this.now + 5;
        if (this.start <= 0) {
            this.start = 1;
        }
        if (this.end > this.count) {
            this.end = this.count;
        }
    }

    public List<T> getDatas() {
        return datas;
    }

    public void setDatas(List<T> datas) {
        this.datas = datas;
    }

    public int getDataCount() {
        return dataCount;
    }

    public int getSize() {
        return size;
    }

    public int getPre() {
        return pre;
    }

    public int getNow() {
        return now;
    }

    public int getCount() {
        return count;
    }

    public int getNext() {
        return next;
    }

    public int getStart() {
        return start;
    }

    public int getEnd() {
        return end;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }
}

Exception Handling

In web.xml

      <error-page>
       <error-code>404</error-code>
        <location>/fileNotfound.jsp</location>
    </error-page>
   
     <error-page>
        <error-code>405</error-code>
        <location>/methodNotfound.jsp</location>
    </error-page>
   
   <error-page>
       <error-code>500</error-code>
       <location>/exception.jsp</location>
   </error-page>
   
   <error-page>
       <exception-type>javax.servlet.ServletException</exception-type>
       <location>/error-xml.jsp</location>
   </error-page>
   
   <!-- 所有异常使用,不推荐这么用 -->
     <error-page>
       <exception-type>java.lang.Throwable</exception-type>
       <location>/throwable-error.jsp</location>
   </error-page>

path

Relative path: ../ (on a directory) ./ (current directory)

Absolute path: / project name / (web project name from the project start, windows system from the beginning of the letter, linux system starting from the root directory)

Links, form forms, redirect using an absolute path

Forwarding not write the project name, the default path in the project

Cookie application

• Server determines whether the user is the same:

　　When the client first accesses the server, the server creates a session, the session id and added to the aggregate response Cookie head, together with the data server to the client Cookie response to the client, the client generally retain this case Cookie information, when the client access server again, this time to bring together information Cookie server, server id Cookie remove the session look for servers have this session, if the session description is the same client.

• Add Cookie:

       String gender = URLEncoder.encode("男", "utf-8");
        
       Cookie cookie1 = new Cookie("username", "lishi");
       Cookie cookie2 = new Cookie("password", "li123");
       Cookie cookie3 = new Cookie("gender", gender);
       resp.addCookie(cookie1);
       resp.addCookie(cookie2);
       resp.addCookie(cookie3);

• Get Cookie:

   Cookie[] cookies = req.getCookies();
       for (Cookie cookie : cookies) {
           String name = cookie.getName();
           String value = URLDecoder.decode(cookie.getValue(), "utf-8");
           resp.getWriter().println("<h3>"+name + "=" + value+"</h3>");
        }

• Cookie life cycle setup

       Cookie cookie1 = new Cookie("username", "lishi");
       cookie1.setMaxAge(120);//单位秒，即2分钟就消失
       Cookie cookie2 = new Cookie("password", "li123");
       cookie2.setMaxAge(0);//只响应到客户端，到了客户端就消失
       Cookie cookie3 = new Cookie("gender", gender);
       cookie3.setMaxAge(-1);//浏览器结束时消失

• The browser sends a path defined Cookie

The default path is the default Cookie Cookie sent with the next file

Set Cookie transmission path cookie.setPath (request.getContextPath ());

• Cookie restrictions

Cookie can be disabled by the user

Cookie saved to visit end unsafe for sensitive data needs to be encrypted before use to save Cookie

Cookie can only save a small amount of data, about 4kb

Cookie restricted number of

Cookie can only be saved string

Chinese decoder decoding

• 译码： String gender = URLEncoder.encode("男", "utf-8");
• 解码： String value = URLDecoder.decode(cookie.getValue(), "utf-8");

Copy the project to modify the access path

Click on the Eclipse Window> show view> Navigator, click to open the project to modify the access path> points to open the settings> org.eclipse.wst.common.component opening the file, modified

<?xml version="1.0" encoding="UTF-8"?>
 <project-modules id="moduleCoreId" project-version="1.5.0">
    <!-- 修改deploy-name属性 -->
    <wb-module deploy-name="day01-26">
        <wb-resource deploy-path="/" source-path="/WebContent" tag="defaultRootSource" />
        <wb-resource deploy-path="/WEB-INF/classes" source-path="/src" />
        <property name="context-root" value="deploy-name属性值" />
       <property name="java-output-path" value="/deploy-name属性值/build/classes" />
    </wb-module>
</project-modules>

Storing, using deploy-name attribute value when accessing the project as the project name to access

session

session stored on the server for storing user to access the server from a browser session information

session for login:

        if ("login".equals(oper)) {
            // 登录
            String username = (String) req.getParameter("username");
            String password = (String) req.getParameter("password");
            String vcode = (String) req.getParameter("vcode");

            if (username != null && username.equals("111") && password != null && password.equals("123")) {
                System.out.println("密码正确!");
                // 密码正确
                if (vcode == null || !vcode.equalsIgnoreCase((String) req.getSession().getAttribute("code"))) {
                    // 验证码不对
                    System.out.println("验证码不对!");
                    req.setAttribute("msg", "验证码输入有误!");
                    req.getRequestDispatcher("login.jsp").forward(req, resp);
                } else {
                    System.out.println("验证码正确!");
                    req.getSession().setAttribute("loginUser", "loginUser");
                    // session.setMaxInactiveInterval(20);//设置不活跃间隔，单位秒
                    req.getRequestDispatcher("list.do").forward(req, resp);
                    // resp.sendRedirect("pageList.do");// 去员工列表
                }
            } else {

                req.setAttribute("msg", "用户名或者密码输入错误!");
                req.getRequestDispatcher("login.jsp").forward(req, resp);
            }
        } else if ("logout".equals(oper)) {
            // 退出登录
            req.getSession().invalidate();
            resp.sendRedirect("login.jsp");
        }

Verification code

public class ValidateCode extends HttpServlet {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public void service(HttpServletRequest request, HttpServletResponse response) throws IOException {
        // 创建空白图片
        BufferedImage image = new BufferedImage(100, 30, BufferedImage.TYPE_INT_RGB);
        // 获取图片画笔
        Graphics g = image.getGraphics();
        Random r = new Random();
        // 设置画笔颜色
        g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
        // 绘制矩形的背景
        g.fillRect(0, 0, 100, 30);
        // 调用自定义的方法，获取长度为5的字母数字组合的字符串
        String number = getNumber(5);
        // 插入session
        HttpSession session = request.getSession();
        session.setAttribute("code", number);
        
        g.setColor(new Color(0, 0, 0));
        g.setFont(new Font(null, Font.BOLD, 24));
        // 设置颜色字体后，绘制字符串
        g.drawString(number, 5, 25);
        // 绘制8条干扰线
        for (int i = 0; i < 8; i++) {
            g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
            g.drawLine(r.nextInt(100), r.nextInt(30), r.nextInt(100), r.nextInt(30));
        }
        response.setContentType("image/jpeg");
        // 写入响应头中
        OutputStream ops = response.getOutputStream();
        ImageIO.write(image, "jpeg", ops);
        ops.close();
    }

    private String getNumber(int size) {
        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        String number = "";
        Random r = new Random();
        for (int i = 0; i < size; i++) {
            number += str.charAt(r.nextInt(str.length()));
        }
        return number;
    }
}

filter

Insertable web component, the filter needs to implement a write Filter interface, a plurality Filter perform the mapping information sequence

Filter advantages: implementation code "pluggable", either to increase or decrease a function module does not affect the normal operation program,

Monitor

• Life cycle events

httpRequestListener

HttpSessionListener

HttpServletContextListener

• Binding data related events

EL expression

And then click Find pagecontext, request, session, application

Calculation: empty is determined whether the air

    用户名:${name}
    用户名:${requestScope.user.name}
    <!-- EL表达式常用的逻辑运算符
    &&或者and 且
    ||或者or  或
    !或者not 非
    ==或者eq 等于
    !=或者ne 不等于
    <或者lt 小于
    >或者gt 大于
    <=或者le 小于等于
    >=或者ge 大于等于
     -->
     <!-- param使用于request.getParameter(arg0) -->
    用户名:${param.name}
    爱好:${paramValues.interest[0]}
    爱好:${paramValues.interest[1]}

JSTL expression

    <!-- if -->
    <c:if test="${user.score.score>=60}" var="s" scope="request">及格</c:if>
    <c:if test="${!s}">不及格</c:if>  <br />
    <!-- 集合遍历count从1开始,index中0开始 -->
    <c:forEach items="${emps}" var="emp" varStatus="s">
        s.count:${s.count} s.index:${s.index} 员工姓名:${emp.uname} 员工职位:${emp.job}<br/>
    </c:forEach>
    
    <!-- if else -->
    <c:choose>
        <c:when test="${user.score.score>=60}">及格</c:when>
        <c:otherwise>不及格</c:otherwise>
    </c:choose>

web project references WEB-INF image below example

jsp页面在

WebRoot\WEB-INF\jsp\foreground\login\newlogin.jsp

在此页面引用 WebRoot\WEB-INF\images\common\下面的图片文件

例子：
<img src="${pageContext.request.contextPath}/images/common/mask.png"/>

即：
<img src="http://192.168.2.106:8180/NEcrd/images/common/mask.png"/>