Servlet详解-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_45378285/article/details/106732719

HTTP请求和响应

what
HttpServletResponse对象
输出中文乱码
- why
- 方法（两种）
网页的定时刷新
- 网页重定向
HttpServletRequest对象
- 获取请求行的相关方法
- 请求头的方法
referer 防盗链
HttpServletRequest应用
请求参数乱码
RequestDispatcher对象
- forward
- include

what

Servlet主要作用就是处理客户端请求，并向客户端做出响应，所以Servlet的每次调用service()方法之前，都会创建两个对象，分别是HttpServeletRequest和HttpServletResponse.
每次Servlet都只会创建一个实例对象，接受一个请求，就会重新创建一个request对象和一个response对象，

HttpServletResponse对象

状态码方法：

setStatus( int status):
sendError(int sc): 发送错误信息的状态码

响应消息头相关方法：

void addHeader(String name,String value):
void setHeader(String name ,String vlaue):
void addIntHeader(String name,int value):
void setIntHeader(String name,int value):
void setContentLength(int len)
void setContentType(String type)
void setLocale(Locale loc) 用于设置响应消息的本地化信息
void setCharacterEncoding(String charset)

发送响应消息体的方法：

getOutputStream()方法：

public class MyHttpServlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String data = "itcast";
        ServletOutputStream outputStream = resp.getOutputStream();
        outputStream.write(data.getBytes());
    }

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

getwriter():

public class MyHttpServlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String data = "itcast";
        //获取字符输出流对象
        PrintWriter writer = resp.getWriter();
        writer.println(data);
    }

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

输出中文乱码

why

computer的数据是以二进制的形式存储，传输文本的时候，发生字符和字节的转换，字符和字节的转换通过查码表完成，字符向字节的转换是编码，字节向字符是解码，编码和解码使用的码表不一致，就会导致乱码问题，这里就相当于response对数据进行编码，使用的是一种码表，而浏览器对数据进行解码使用的是另一种码表，导致中文乱码。、

方法（两种）

第一种

        resp.setCharacterEncoding("utf-8");
        resp.setHeader("Content-Type","text/html;charset=utf-8");

第二种

resp.setContentType("text/html;charset=utf-8");

代码

public class MyHttpServlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String data = "itcast";
        //获取字符输出流对象
        PrintWriter writer = resp.getWriter();
        /*第一种*/
        resp.setContentType("text/html;charset=utf-8");
        /*第二种*/
        resp.setCharacterEncoding("utf-8");
        resp.setHeader("Content-Type","text/html;charset=utf-8");
        writer.println(data);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}

网页的定时刷新

setHeader(“Refresh”,“2,URL=http://www.bia.com”);

public class MyHttpServlet3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //两秒后，跳转到指定页面
        resp.setHeader("Refresh","2,URL=http://www.it.com");
    }

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

public class MyHttpServlet4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 每个三秒定时刷新当前网页
        resp.setHeader("Refresh","3");
        resp.getWriter().println(new java.util.Date().toLocaleString());
    }

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

网页重定向

sendRedirect()：方法
在这里插入图片描述

代码
login.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="/chapter04/MyHttpServlet5" method="post">
    用户名：<input type="text" name="username"/><br/>
    密&nbsp;&nbsp;&nbsp;码：<input type="password" name="password"/><br/>
    <input type="submit" value="登录">

</form>
</body>
</html>

welcome.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>登录成功，欢迎您！</h1>
</body>
</html>

MyHttpServlet5

public class MyHttpServlet5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //用HttpServletRequest对象的getParameter（）方法获取用户名和密码
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        if("itcast".equals(username) && "123".equals(password)){
            //密码和用户名正确，跳转到欢迎页面
            resp.sendRedirect("/chatper04/welcome.html");
        }else {
            //不正确，跳转到登录页面
            resp.sendRedirect("/chapter04/login.html");
        }
    }

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

HttpServletRequest对象

获取请求行的相关方法

public class MyHttpServlet6 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        /*HTTP请求种请求方式*/
        writer.println(req.getMethod());
        /*资源名称部分，主机号和端口号之后，参数部分之前*/
        writer.println(req.getRequestURI());
        /*参数部分*/
        writer.println(req.getQueryString());
        /*协议名和版本号*/
        writer.println(req.getProtocol());
        /*请求URL中属于web应用的路径*/
        writer.println(req.getContextPath());
        /*Servlet的名称和映射路径*/
        writer.println(req.getServletPath());
        /*主机的ip地址*/
        writer.println(req.getRemoteAddr());
        /*客户端的完整主机名*/
        writer.println(req.getRemoteHost());
        /*客户端的网络连接的端口号*/
        writer.println(req.getRemotePort());
        /*web服务器上的当前网络连接的ip地址*/
        writer.println(req.getLocalAddr());
        /*web服务器上的当前网络连接的对应的主机号*/
        writer.println(req.getLocalName());
        /*web服务器上的当前网络连接的对应的端口号*/
        writer.println(req.getLocalPort());
        /*host字段中对应的主机名*/
        writer.println(req.getServerName());
        /*host字段中对应的端口号*/
        writer.println(req.getServerPort());
        /*请求的协议名 例如：http*/
        writer.println(req.getScheme());
        /*完整的路径*/
        writer.println(req.getRequestURL());
    }

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

请求头的方法

String getHeader(String name):
Enumeration getHeaders(String name)
Enumeration getHeaderNames()
int getIntHeader(String name)
long getDateHeader(String name)
String getContentType()
int getContentLength()
String getCharacterEncoding()

public class MyHttpServlet7 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        //获取请求消息头中的所有字段
        Enumeration<String> headerNames = req.getHeaderNames();
        //遍历
        while (headerNames.hasMoreElements()){
            String name = headerNames.nextElement();
            String value = req.getHeader(name);
            writer.println(name + ":" + value);
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}

referer 防盗链

public class MyHttpServlet8 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter writer = resp.getWriter();
        //获取referer头
        String referer = req.getHeader("referer");
        //提取访问地址
        String serverName = req.getServerName();
        String url ="http://" + serverName;
        //判断referer是否为空，这个头的首地址是否是自己的
        if(referer != null && referer.startsWith(url)){
            writer.println("download");
        }else {
            //防盗链，跳转到自己的网页
            RequestDispatcher requestDispatcher = req.getRequestDispatcher("/download.html");
            requestDispatcher.forward(req,resp);
        }
    }

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

HttpServletRequest应用

getParameter（String name）
get[ara,eterValues(String name)
getParameterNames()
getParameterMap()
setAtrtibute()
getAttribute()
removeAttribute()
getAttributeNames()
form.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="/chapter04/MyHttpServlet9" method="get">
    用户名：<input type="text" name="username"><br/>
    密码：<input type="password" name="password"><br/>
    兴趣：<input type="checkbox" name="hobby" value="sing">唱歌
          <input type="checkbox" name="hobby" value="game">游戏
          <input type="checkbox" name="hobby" value="dance">跳舞
            <input type="submit" value="get"/>

</form>
</body>
</html>

public class MyHttpServlet9 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username + ":" + password);
        String[] hobbies = req.getParameterValues("hobby");
        System.out.println("爱好：");
        for(int i = 0;i<hobbies.length;i++){
            System.out.println(hobbies[i]);
        }
    }

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

请求参数乱码

req.setCharacterEncoding("utf-8");

RequestDispatcher对象

getRequestDispatcher(String path) : 返回封装了路径所指定资源的RequestDispatcher对象
创建了对象之后，要通知其他Web资源对该Servlet请求进行处理，为此有两个方法
forward(req,resq);请求从一个Servlet传递给另一个Web资源
include(req,resq); 将其他资源作为当前响应内容包含进来

forward

public class MyHttpServlet10 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        req.setAttribute("username","chen");
        RequestDispatcher requestDispatcher = req.getRequestDispatcher("/MyHttpServlet11");
        requestDispatcher.forward(req,resp);
    }

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

public class MyHttpServlet11 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        String username = (String) req.getAttribute("username");
        if(username != null ){
            resp.getWriter().println(username);
        }
    }

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

include

public class MyHttpServlet10 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
//        req.setAttribute("username","chen");
        RequestDispatcher requestDispatcher = req.getRequestDispatcher("/MyHttpServlet11?username=123");
        requestDispatcher.include(req,resp);
    }

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

public class MyHttpServlet11 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        req.setCharacterEncoding("utf-8");
        String username = (String) req.getAttribute("username");
        if(username != null ){
            resp.getWriter().println(username);
        }
        resp.getWriter().println(req.getQueryString());
    }

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

1、请求转发与重定向的异同点如下：
1）	请求转发和重定向都可以实现访问一个资源时转向当前应用资源
2）	请求转发是一次请求一次响应，而重定向为两次请求两次响应
3）一般情况下应该使用请求转发，减少浏览器对服务器的访问，减轻服务器压力
4）如果需要改变浏览器的地址栏，或更改浏览器的刷新按钮的功能时需要使用重定向

2、禁止浏览器缓存页面的核心代码如下：
response.setDateHeader("Expires",0);
response.setHeader("Cache-Control","no-cache"); 
response.setHeader("Pragma","no-cache");
重定向后，地址栏显示index.jsp
3、实现代码如下：
（1）MyServlet程序类如下：
public class MyServlet extends HttpServlet {
	protected void doGet(HttpServletRequest request, 
HttpServletResponse response)throws ServletException, IOException {
		System.out.println("这里是MyServlet！");
		response.sendRedirect(request.getContextPath() + "/index.jsp");
	}
}
（2）web.xml文件配置如下：
<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>
        cn.itcast.chapter04.servlet.MyServlet
    </servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
</servlet-mapping>

4、该功能的实现步骤如下：
1）创建一个DownManagerServlet类，使其继承HttpServlet类并重写该类的doGet()方法。
2）在doGet()方法中，使用HttpServletRequest对象的getHeader("referer")方法得到字段referer的值，并判断是否可以进行资源下载。
3）如果不能下载，则进入下载页（需要在Eclipse的WebContent目录下创建一个download.html）。
（1）DownManagerServlet类的实现代码如下：
public class DownManagerServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		// 获取referer头的值
		String referer = request.getHeader("referer");
		// 获取访问地址
		String sitePart = "http://" + request.getServerName();
		if (referer != null && referer.startsWith(sitePart)) {
			// 处理正在下载的请求
			out.println("dealing download ...");
		} else {
			// 非法下载请求跳转到download.html页面
			RequestDispatcher rd = request
					.getRequestDispatcher("/download.html");
			rd.forward(request, response);
		}
	}
}
（2）web.xml文件中DownManagerServlet的映射信息配置如下：
<servlet>
    <servlet-name>DownManagerServlet</servlet-name>
    <servlet-class>
        cn.itcast.chapter04.servlet.DownManagerServlet
    </servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>DownManagerServlet</servlet-name>
    <url-pattern>/DownManagerServlet</url-pattern>
</servlet-mapping>