15-常用代码片段

目录

pom.xml

web.xml

hello world

读取请求报头

读取 GET 请求的 query string

读取 POST 请求的 body

设置状态码

设置响应报头

重定向

登陆页面

创建新 Session

获取已有 Session

上传文件

---

此处把⼀些常⽤代码⽚段罗列在这⾥，后续写代码的时候可以在这个基础上拷⻉过去直接修改。

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.bit</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>
    <!-- 指定属性信息 -->
    <properties>
        <encoding>UTF-8</encoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
    <dependencies>
        <!-- 加⼊ servlet 依赖 -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <!-- servlet 版本和 tomcat 版本有对应关系，切记 -->
            <version>3.1.0</version>
            <!-- 这个意思是我们只在开发阶段需要这个依赖，部署到 tomcat 上时就不需要了 -->
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.45</version>
        </dependency>
        <!--https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.12.3</version>
        </dependency>
    </dependencies>
    <!-- 打包⽅式是 war 包，⼀种⽤于 web 应⽤的包，原理类似 jar 包 -->
    <packaging>war</packaging>
    <build>
        <!-- 指定最终 war 包的名称 -->
        <finalName>test</finalName>
    </build>
</project>

web.xml

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
    <display-name>Archetype Created Web Application</display-name>
</web-app>

hello world

@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("hello");
   }
}

读取请求报头

@WebServlet("/getParameter")
public class GetParameter extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String contentType = req.getHeader("Content-Type");
        // 或者使⽤
        String contentType = req.getContentType();
   }
}

读取 GET 请求的 query string

@WebServlet("/getParameter")
public class GetParameter extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String userId = req.getParameter("userId");
        String classId = req.getParameter("classId");
   }
}

读取 POST 请求的 body

@WebServlet("/postParameter")
public class PostParameter extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html; charset=utf-8");
        req.setCharacterEncoding("utf-8");
        String userId = req.getParameter("userId");
        String classId = req.getParameter("classId");
        resp.getWriter().write("userId: " + userId + ", " + "classId: " +
classId);
   }
}

设置状态码

@WebServlet("/statusServlet")
public class StatusServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setStatus(200);
   }
}

设置响应报头

@WebServlet("/autoRefreshServlet")
public class AutoRefreshServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("Refresh", "1");
   }
}

重定向

@WebServlet("/redirectServlet")
public class RedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("http://www.sogou.com");
   }
}

登陆页面

<form action="login" method="POST">
    <input type="text" name="username">
    <input type="password" name="password">
    <input type="submit" value="提交">
</form>

创建新 Session

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession(true);
        session.setAttribute("username", "admin");
        session.setAttribute("loginCount", "0");
   }
}

获取已有 Session

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    HttpSession session = req.getSession(false);
    if (session == null) {
        // ⽤户没有登陆, 重定向到 login.html
        resp.sendRedirect("login.html");
        return;
    }
    // 如果已经登陆, 则从 Session 中取出数据
    String userName = (String)session.getAttribute("username");
    String countString = (String)session.getAttribute("loginCount");
}

上传文件

@MultipartConfig
@WebServlet("/upload")
public class UploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Part part = req.getPart("MyImage");
        System.out.println(part.getSubmittedFileName());
        System.out.println(part.getContentType());
        System.out.println(part.getSize());
        part.write("d:/MyImage.jpg");
        resp.getWriter().write("upload ok");
   }
}

<form action="upload" enctype="multipart/form-data" method="POST">
    <input type="file" name="MyImage">
    <input type="submit" value="提交图⽚">
</form>