LearnGuide

一、Servlet App 从入门到入土

使用Maven创建项目(IDEA或者VSCODE)

shell

.
├── pom.xml
└── src
    └── main
        ├── resources
        └── webapp
            ├── index.jsp
            └── WEB-INF
                └── web.xml

编辑pom.xml，在dependencies节点添加目前最新的servlet包、Jsp包（2024-03-05）

xml

<!-- https://mvnrepository.com/artifact/jakarta.servlet/jakarta.servlet-api -->
<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>6.0.0</version>
    <scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/jakarta.servlet.jsp/jakarta.servlet.jsp-api -->
<dependency>
    <groupId>jakarta.servlet.jsp</groupId>
    <artifactId>jakarta.servlet.jsp-api</artifactId>
    <version>3.1.1</version>
    <scope>provided</scope>
</dependency>

添加Tomcat服务器

shell

.
├── pom.xml
└── src
    └── main
        ├── java
        │   └── com
        │       └── bean
        │           └── servlet
        │               └── HelloServlet.java
        └── webapp
            ├── index.jsp
            └── WEB-INF
                └── web.xml

编辑HelloServlet.java文件

java

package com.bean.servlet;

import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("进入doGET方法");
        PrintWriter out = resp.getWriter();
        out.print("hello servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

编辑src/main/webapp/WEB-INF/web.xml

xml

<web-app>
    <!-- servlet配置 -->
    <servlet>
        <!-- servlet唯一别名 -->
        <servlet-name>hello</servlet-name>
        <!-- servlet包位置 -->
        <servlet-class>com.bean.servlet.HelloServlet</servlet-class>
    </servlet>
    <!-- 网站服务映射 -->
    <servlet-mapping>
        <!-- servlet唯一别名 -->
        <servlet-name>hello</servlet-name>
        <!-- 浏览器匹配规则，匹配上次规则，则查找对应的servlet -->
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

如果希望两个请求连接指向同一个Servlet服务，可以这样编解

xml

<web-app>
    <!-- servlet配置 -->
    <servlet>
        <!-- servlet唯一别名 -->
        <servlet-name>hello</servlet-name>
        <!-- servlet包位置 -->
        <servlet-class>com.bean.servlet.HelloServlet</servlet-class>
    </servlet>

    <!-- 网站服务映射 -->
    <servlet-mapping>
        <!-- servlet唯一别名 -->
        <servlet-name>hello</servlet-name>
        <!-- 浏览器匹配规则，匹配上次规则，则查找对应的servlet -->
        <url-pattern>/hello1</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello2</url-pattern>
    </servlet-mapping>
</web-app>

查找方案：

shell

1. 浏览器请求
2. servlet-mapping(url-pattern)进行匹配
3. 匹配成功后获取到servlet-name
4. servlet(servlet-name)进行查找
5. 找到servlet-class
6. 执行对应class文件，并将结果返回给浏览器界面

编译启动，打开浏览器查看

二、Servlet getServletContext方法

数据共享

java

// 获取上下文
ServletContext context = this.getServletContext();

context.setAttribute("name", "tom");
System.out.println((String)context.getAttribute("name"));

获取Servlt上下文getServletContext

编辑src/main/webapp/WEB-INF/web.xml

xml

<web-app>
    <!-- 添加context-param -->
    <context-param>
        <param-name>jdbc</param-name>
        <param-value>jdbc:mysql://127.0.0.1/webdb</param-value>
    </context-param>

    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.bean.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

通过getServletContext方法获取web.xml中的数据

java

// 获取上下文
ServletContext context = this.getServletContext();
System.out.println(context.getInitParameter("jdbc")); // jdbc:mysql://127.0.0.1/webdb

请求转发（非重定向）

java

// 获取上下文
ServletContext context = this.getServletContext();
context.getRequestDispatcher("/hello2").forward(req, resp);

读取资源文件

java

// 在src/main/resources下创建一个配置文件 db.properties
// 在应用中加载本地资源
InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties")
Properties properties = new Properties();
properties.load(in);
System.out.println(properties.getProperty("username"));
System.out.println(properties.getProperty("password"));

三、HttpServletResponse

四、HttpServletRequest

java

// 获取cookie
req.getCookies();
// 设置cookie
resp.addCookie();

六、Session

java

// 获取session对象
HttpSession session = req.getSession();
// 为session对象设置值
session.setAttribute();
// 获取session对象的值
session.getAttribute();
// 设置session过期
session.invalidate();

编辑src/main/webapp/WEB-INF/web.xml

xml

<!--  设置session配置  -->
<session-config>
    <!--    设置1分钟过期    -->
    <session-timeout>1</session-timeout>
</session-config>

七、过滤器

编辑过滤器

java

// HelloFilter01
package com.bean.filter;

import jakarta.servlet.*;

import java.io.IOException;

public class HelloFilter01 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("HelloFilter01 init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("HelloFilter01 进入Servlet前的处理");

        // 进入下一个过滤器，否则程序终止
        filterChain.doFilter(servletRequest, servletResponse);

        System.out.println("HelloFilter01 doFilter之后的处理");
    }

    @Override
    public void destroy() {
        System.out.println("HelloFilter01 destroy");
    }
}

java

// HelloFilter02
package com.bean.filter;

import jakarta.servlet.*;

import java.io.IOException;

public class HelloFilter02 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("HelloFilter02 init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("HelloFilter02 进入Servlet前的处理");

        // 进入下一个过滤器，否则程序终止
        filterChain.doFilter(servletRequest, servletResponse);

        System.out.println("HelloFilter02 doFilter之后的处理");
    }

    @Override
    public void destroy() {
        System.out.println("HelloFilter02 destroy");
    }
}

编辑web.xml

xml

<web-app>
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.bean.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>HelloServletTestFilter</servlet-name>
        <servlet-class>com.bean.servlet.HelloServletTestFilter</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloServletTestFilter</servlet-name>
        <url-pattern>/filter</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>HelloServletTestFilter</servlet-name>
        <url-pattern>/ufilter/filter</url-pattern>
    </servlet-mapping>


    <!-- 过滤器 -->
    <filter>
        <filter-name>filter01</filter-name>
        <filter-class>com.bean.filter.HelloFilter01</filter-class>
    </filter>
    <!-- 过滤器映射 -->
    <filter-mapping>
        <filter-name>filter01</filter-name>
        <!-- 当请求进入/ufilter开头的路径时，开始使用过滤器 -->
        <url-pattern>/ufilter/*</url-pattern>
    </filter-mapping>
    <filter>
        <filter-name>filter02</filter-name>
        <filter-class>com.bean.filter.HelloFilter02</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter02</filter-name>
        <!-- 当请求进入/ufilter开头的路径时，开始使用过滤器 -->
        <url-pattern>/ufilter/*</url-pattern>
    </filter-mapping>
</web-app>

使用结果
使用总结
过滤器的doFilter方法中第三个参数FilterChain,通过传入req、resp参数进入下一轮过滤器
请求进来时，先进入过滤器（可能多个），然后进入Servlet，最后还是通过过滤器返回回来之后响应至前端。过滤器有点类似洋葱模型的感觉

一、Servlet App 从入门到入土 ​

二、Servlet getServletContext方法 ​

三、HttpServletResponse ​

四、HttpServletRequest ​

五、Cookie ​

六、Session ​

七、过滤器 ​

一、Servlet App 从入门到入土

二、Servlet getServletContext方法

三、HttpServletResponse

四、HttpServletRequest

五、Cookie

六、Session

七、过滤器