Servlet进阶-下 – 源码巴士

Cookie作用

Cookie:提供浏览器关闭后数据不会丢失的机制

Cookie:默认与域名绑定，只有域名下的程序才能读取数据

Cookie时效性

Cookie:具有时效性，Cookie会伴随请求头发送给服务器

Cookie:默认情况下Cookie有效期与当前浏览器进程绑定

Cookie:设置过期时间后，Cookie过期后才会失效

如何看网页存在的Cookie

查看网页旁边的小锁就可以看到有哪些cookie

如何自己向网页添加Cookie

设置cookie:

Cookie cookie=new Cookie("random",String.valueOf(random));//cookie名字与cookie值

添加cookie:

resp.addCookie(cookie);

设置最大生存时间:

cookie.setMaxAge(60*60*24);//设置最大生存时间

@WebServlet("/cookie/random1")
public class RandomServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Integer random=new Random().nextInt(10000);
        Cookie cookie=new Cookie("random",String.valueOf(random));
        cookie.setMaxAge(60*60*24);//设置最大生存时间
        resp.addCookie(cookie);
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().println("<h2>生成的随机数为:"+random+"</h2>");
    }
}

如何自己向网页提取Cookie

提取操作：

Cookie[] cookies = req.getCookies();
for (Cookie c:cookies){
    if (c.getName().equals("random"))
        random= Integer.parseInt(c.getValue());
}

验证操作(因为cookie被销毁后去获取cookie的话会报500错误)

if (cookies == null){
    resp.getWriter().println("未包含任何数据");
    return;
}

@WebServlet("/cookie/show1")
public class CookieServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        Cookie[] cookies = req.getCookies();
        Integer random=-1;
        if (cookies == null){
            resp.getWriter().println("未包含任何数据");
            return;
        }
        for (Cookie c:cookies){
            if (c.getName().equals("random"))
                random= Integer.parseInt(c.getValue());
        }
        resp.getWriter().println("<h2>name=random的cookie值为:"+random+"</h2>");
    }
}

Session作用

1.保密性更高，数据保存在服务器内存中，相当于钱存银行

2.默认时长为30分钟。Cookie默认时长为浏览器进程

3.Seesion通过浏览器Cookie的SeesionId值提取用户数据

4.session.setAttribute设置的属性生存周期与应用范围比自定义属性（request.setAttribute）更广

Session常用方法

创建session

@WebServlet("/session/random")
public class RandomServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Integer random=new Random().nextInt(10000);
        HttpSession session = req.getSession();//创建session
        session.setAttribute("random",random);//设置session值
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().println("<h2>随机数"+random+"已生成</h2>");
    }
}

获取session

@WebServlet("/session/show")
public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        Integer random = (Integer)session.getAttribute("random");
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().println("name=random的session值为:"+random);
    }
}

ServletContext作用

一般用于网站恒定不变的备用信息

设置ServletContext

@WebServlet("/servletcontext/init")
public class ServletContextInitServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext=request.getServletContext();
        servletContext.setAttribute("laodi","老弟");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("ServletContext已初始化");
    }
}

提取ServletContext

@WebServlet("/servletcontext/index")
public class IndexServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        ServletContext context=request.getServletContext();
        String laodi = (String)context.getAttribute("laodi");
        PrintWriter out= response.getWriter();
        out.println(laodi);
    }
}

设置web应用默认首页-->在xml中加入以下代码设置

    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>login.html</welcome-file>
    </welcome-file-list>

设置404,500等状态码默认页面

    <error-page>
        <error-code>404</error-code>
        <location>/error/404.html</location>
    </error-page>
    <error-page>
        <error-code>500</error-code>
        <location>/error/500.html</location>
    </error-page>

设置启动时加载Servlet

代码一

    <servlet>
        <servlet-name>initTable</servlet-name>
        <servlet-class>startup.InitTableServlet</servlet-class>
        <!--        自定义参数-->
        <init-param>
            <param-name>database</param-name>
            <param-value>db01</param-value>
        </init-param>
        <!--        设置启动时加载,且定义优先级-->
        <load-on-startup>0</load-on-startup>
    </servlet>

public class InitTableServlet extends HttpServlet {
    @Override
    public void init(ServletConfig config) throws ServletException {
        String database = config.getInitParameter("database");
        System.out.println("正在向"+database+"创建数据表...");
    }
}

代码二

    <servlet>
        <servlet-name>import</servlet-name>
        <servlet-class>startup.ImportServlet</servlet-class>
        <init-param>
            <param-name>file</param-name>
            <param-value>c:/tmp/demo.txt</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

public class ImportServlet extends HttpServlet {
    @Override
    public void init(ServletConfig config) throws ServletException {
        String file = config.getInitParameter("file");
        System.out.println("正在导入"+file+"数据...");
    }
}

JavaWeb的打包与发布

1.利用maven打包

2.利用maven清理包-->点击clean

3.maven打包时一般为jar包，需要在pom.xml文件中定义打包输入为war包

<packaging>war</packaging>

4.如果遇到打包失败时请在pom.xml文件中加入以下代码

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.2.0</version>
            </plugin>
        </plugins>
    </build>

如何定义某些jar包文件不被重复打包

如何更改war包输出的名字

    <build>
        <finalName>web-setvlet</finalName>
    </build>

如何打开包好的war包

1.打开文件夹

如何运行包好的war包

1.复制这个war包

2.来到webapps目录，粘贴在里面

3.来到bin目录下的starup打开-->此时刚刚的war包会被自动解压缩,双击打开进入即可

此时这个war包就已经在运行了

4.默认情况下进入此时包内的网页时需要如下加入包名-->但是此时就出现了一个问题，跳转到包内其他网页时，包名不会被输入

所以此时需要进入conf目录设置访问上下文路径

步骤：tomcat-->conf-->server.xml-->在</Host>上方加入以下代码即可

原文链接：https://blog.csdn.net/m0_63042689/article/details/126999058