20210121 JavaWeb之Servlet 详解第二部分
作者：互联网
6 、Servlet
6.1 Servlet简介
- Servlet就是sun公司开发动态web的一门技术
- Sun在这些API中提供一个接口叫做：Servlet，如果你想开发一个servler程序，只需要完成两个步骤：
- 编写一个类，实现Servlet接口
- 把开发好的Java类部署到web服务器中
把实现了Servlet接口的Java程序叫做，Servlet
6.2 HelloServlet
Servlet接口Sun公司有两个默认的实现类：HttpServlet GenericServlet
-
构建一个普通的Maven项目，删掉里面的src目录，以后我们的学习就在这个项目里建立Moudle;这个空的工程就是Maven主工程
-
关于Maven父子工程的理解
-
父项目中会有
<modules> <module>servlet01</module> </modules> -
子项目中会有
<parent> <artifactId>javaweb-01-servlet</artifactId> <groupId>com.gdh</groupId> <version>1.0-SNAPSHOT</version> </parent>
-
父项目中的java子项目可以直接使用 son extends father
-
Maven环境优化
- 修改web.xml为最新的
- 将maven的结构搭建完整
-
编写一个Servlet程序
- 编写一个普通类
- 实现servlet接口,直接继承HttpServlet
public class HelloServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doGet(req, resp);
// ServletOutputStream outputStream = resp.getOutputStream();
PrintWriter writer = resp.getWriter();//响应流
writer.print("Hellr world");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
-
编写Serverlet的映射
为什么需要映射：我们写的JAVA程序，但是要通过浏览器访问，而浏览器需要连接web服务器，所以我们需要在web服务器中注册我们写的Servlet,还需要给他一个浏览器能够访问的路径；
<!--注册servlet--> <servlet> <servlet-name>helloServlet</servlet-name> <servlet-class>com.dyt.servlet.HelloServlet</servlet-class> </servlet> <!--一个servlet对应一个mapping映射--> <servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>/hello</url-pattern> </servlet-mapping> -
配置tomcat
-
启动项目测试
6.3 Servlet原理
Servlet是由Web服务器调用，web服务器在收到浏览器请求之后，会
6.4 Mapping问题
-
一个Servlet可以指定一个映射路径
<servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>/hello</url-pattern> </servlet-mapping> -
一个Servlet可以指定多个映射路径
<servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>/hello</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>/hello1</url-pattern> </servlet-mapping> -
一个Servlet可以指定通用映射路径
<servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>/hello/*</url-pattern> </servlet-mapping> -
指定一些后缀或者前缀
<!--可以自定义后缀实现请求映射 *前边不能加项目映射的路径 ssss.gdh--> <servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>*.gdh</url-pattern> </servlet-mapping> -
默认请求路径
<servlet-mapping> <servlet-name>helloServlet</servlet-name> <!--请求路径--> <url-pattern>/*</url-pattern> </servlet-mapping> -
优先级问题
指定了固有的映射路径优先级最高，如果找不到就会走默认的处理请求；
<!--404处理--> <servlet> <servlet-name>error</servlet-name> <servlet-class>com.gdh.servlet.ErrorServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>error</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping>
6.5 ServletContext
web容器在启动的时候，它会为每个web程序都创建一个对应的ServletContext对象，它代表了当前的web应用。可以保存一下数据
-
共享数据
在这个servlet中保存的数据，可以在另外一个servlet中拿到
public class HelloServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("HelloServlet.doGet"); //this.getServletConfig(); //servlet配置 //this.getInitParameter("我的一个Servlet"); //初始化参数 ServletContext conext = this.getServletContext();//servlet上下文 String name = "我的一个Servlet"; //将一个数据保存在ServletContext中，名字为s1 值为name conext.setAttribute("s1",name); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }public class GetServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext context = this.getServletContext(); String s1 = (String) context.getAttribute("s1"); resp.setContentType("text/html"); resp.setCharacterEncoding("utf-8"); resp.getWriter().print("名字:"+s1); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }<servlet> <servlet-name>hello</servlet-name> <servlet-class>com.gdh.servlet.HelloServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping> <servlet> <servlet-name>context</servlet-name> <servlet-class>com.gdh.servlet.GetServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>context</servlet-name> <url-pattern>/context</url-pattern> </servlet-mapping>测试访问： 先http://localhost:8080/s2/hello 再http://localhost:8080/s2/context 结果如下
-
获取初始化参数
<!--配置一些web应用初始化参数--> <context-param> <param-name>url</param-name> <param-value>jdbc:mysql://localhost:3306/mybatis</param-value> </context-param>@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext context = this.getServletContext(); String url = context.getInitParameter("url"); resp.getWriter().print(url); } -
请求转发
@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext context = this.getServletContext(); /* 请求转发路径 RequestDispatcher dispatcher = context.getRequestDispatcher("/g"); 调用forward实现请求转发 dispatcher.forward(req,resp);*/ context.getRequestDispatcher("/g").forward(req,resp); } -
读取资源文件
Properties 在java目录下新建properties 在resources目录下新建properties 发现：都被打包到了同一路径下：classes 我们俗称这个路径为classpath 思路：需要一个文件流读取properties中内容username=gdh password=123@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext context = this.getServletContext(); /* 请求转发路径 RequestDispatcher dispatcher = context.getRequestDispatcher("/g"); 调用forward实现请求转发 dispatcher.forward(req,resp);*/ // context.getRequestDispatcher("/g").forward(req,resp); InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties"); Properties properties = new Properties(); properties.load(is); String username = properties.getProperty("username"); String password = properties.getProperty("password"); resp.getWriter().print(username +":"+password); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } 测试访问就可以
6.6 HttpServletResponse
web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse；
- 要获取客户端请求过来的参数 找HttpServletRequest
- 如果要给客户端响应一些信息 找HttpServletResponse
1.简单分类
负责向浏览器发送数据的方法
public ServletOutputStream getOutputStream() throws IOException; //用于文件流
public PrintWriter getWriter() throws IOException; //用于写中文
负责向浏览器发送响应头的方法
public void setCharacterEncoding(String charset); //设置响应编码
public void setContentLength(int len); //设置字符串响应的长度
public void setContentLengthLong(long len); //设置长度
public void setContentType(String type); //设置类型
public void setDateHeader(String name, long date);
public void addDateHeader(String name, long date);
public void setHeader(String name, String value);
public void addHeader(String name, String value);
public void setIntHeader(String name, int value);
public void addIntHeader(String name, int value);
响应状态码
public static final int SC_CONTINUE = 100;
/**
* Status code (101) indicating the server is switching protocols
* according to Upgrade header.
*/
public static final int SC_SWITCHING_PROTOCOLS = 101;
/**
* Status code (200) indicating the request succeeded normally.
*/
public static final int SC_OK = 200;
/**
* Status code (201) indicating the request succeeded and created
* a new resource on the server.
*/
public static final int SC_CREATED = 201;
/**
* Status code (202) indicating that a request was accepted for
* processing, but was not completed.
*/
public static final int SC_ACCEPTED = 202;
/**
* Status code (203) indicating that the meta information presented
* by the client did not originate from the server.
*/
public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;
/**
* Status code (204) indicating that the request succeeded but that
* there was no new information to return.
*/
public static final int SC_NO_CONTENT = 204;
/**
* Status code (205) indicating that the agent <em>SHOULD</em> reset
* the document view which caused the request to be sent.
*/
public static final int SC_RESET_CONTENT = 205;
/**
* Status code (206) indicating that the server has fulfilled
* the partial GET request for the resource.
*/
public static final int SC_PARTIAL_CONTENT = 206;
/**
* Status code (300) indicating that the requested resource
* corresponds to any one of a set of representations, each with
* its own specific location.
*/
public static final int SC_MULTIPLE_CHOICES = 300;
/**
* Status code (301) indicating that the resource has permanently
* moved to a new location, and that future references should use a
* new URI with their requests.
*/
public static final int SC_MOVED_PERMANENTLY = 301;
/**
* Status code (302) indicating that the resource has temporarily
* moved to another location, but that future references should
* still use the original URI to access the resource.
*
* This definition is being retained for backwards compatibility.
* SC_FOUND is now the preferred definition.
*/
public static final int SC_MOVED_TEMPORARILY = 302;
/**
* Status code (302) indicating that the resource reside
* temporarily under a different URI. Since the redirection might
* be altered on occasion, the client should continue to use the
* Request-URI for future requests.(HTTP/1.1) To represent the
* status code (302), it is recommended to use this variable.
*/
public static final int SC_FOUND = 302;
/**
* Status code (303) indicating that the response to the request
* can be found under a different URI.
*/
public static final int SC_SEE_OTHER = 303;
/**
* Status code (304) indicating that a conditional GET operation
* found that the resource was available and not modified.
*/
public static final int SC_NOT_MODIFIED = 304;
/**
* Status code (305) indicating that the requested resource
* <em>MUST</em> be accessed through the proxy given by the
* <code><em>Location</em></code> field.
*/
public static final int SC_USE_PROXY = 305;
/**
* Status code (307) indicating that the requested resource
* resides temporarily under a different URI. The temporary URI
* <em>SHOULD</em> be given by the <code><em>Location</em></code>
* field in the response.
*/
public static final int SC_TEMPORARY_REDIRECT = 307;
/**
* Status code (400) indicating the request sent by the client was
* syntactically incorrect.
*/
public static final int SC_BAD_REQUEST = 400;
/**
* Status code (401) indicating that the request requires HTTP
* authentication.
*/
public static final int SC_UNAUTHORIZED = 401;
/**
* Status code (402) reserved for future use.
*/
public static final int SC_PAYMENT_REQUIRED = 402;
/**
* Status code (403) indicating the server understood the request
* but refused to fulfill it.
*/
public static final int SC_FORBIDDEN = 403;
/**
* Status code (404) indicating that the requested resource is not
* available.
*/
public static final int SC_NOT_FOUND = 404;
/**
* Status code (405) indicating that the method specified in the
* <code><em>Request-Line</em></code> is not allowed for the resource
* identified by the <code><em>Request-URI</em></code>.
*/
public static final int SC_METHOD_NOT_ALLOWED = 405;
/**
* Status code (406) indicating that the resource identified by the
* request is only capable of generating response entities which have
* content characteristics not acceptable according to the accept
* headers sent in the request.
*/
public static final int SC_NOT_ACCEPTABLE = 406;
/**
* Status code (407) indicating that the client <em>MUST</em> first
* authenticate itself with the proxy.
*/
public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
/**
* Status code (408) indicating that the client did not produce a
* request within the time that the server was prepared to wait.
*/
public static final int SC_REQUEST_TIMEOUT = 408;
/**
* Status code (409) indicating that the request could not be
* completed due to a conflict with the current state of the
* resource.
*/
public static final int SC_CONFLICT = 409;
/**
* Status code (410) indicating that the resource is no longer
* available at the server and no forwarding address is known.
* This condition <em>SHOULD</em> be considered permanent.
*/
public static final int SC_GONE = 410;
/**
* Status code (411) indicating that the request cannot be handled
* without a defined <code><em>Content-Length</em></code>.
*/
public static final int SC_LENGTH_REQUIRED = 411;
/**
* Status code (412) indicating that the precondition given in one
* or more of the request-header fields evaluated to false when it
* was tested on the server.
*/
public static final int SC_PRECONDITION_FAILED = 412;
/**
* Status code (413) indicating that the server is refusing to process
* the request because the request entity is larger than the server is
* willing or able to process.
*/
public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;
/**
* Status code (414) indicating that the server is refusing to service
* the request because the <code><em>Request-URI</em></code> is longer
* than the server is willing to interpret.
*/
public static final int SC_REQUEST_URI_TOO_LONG = 414;
/**
* Status code (415) indicating that the server is refusing to service
* the request because the entity of the request is in a format not
* supported by the requested resource for the requested method.
*/
public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;
/**
* Status code (416) indicating that the server cannot serve the
* requested byte range.
*/
public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
/**
* Status code (417) indicating that the server could not meet the
* expectation given in the Expect request header.
*/
public static final int SC_EXPECTATION_FAILED = 417;
/**
* Status code (500) indicating an error inside the HTTP server
* which prevented it from fulfilling the request.
*/
public static final int SC_INTERNAL_SERVER_ERROR = 500;
/**
* Status code (501) indicating the HTTP server does not support
* the functionality needed to fulfill the request.
*/
public static final int SC_NOT_IMPLEMENTED = 501;
/**
* Status code (502) indicating that the HTTP server received an
* invalid response from a server it consulted when acting as a
* proxy or gateway.
*/
public static final int SC_BAD_GATEWAY = 502;
/**
* Status code (503) indicating that the HTTP server is
* temporarily overloaded, and unable to handle the request.
*/
public static final int SC_SERVICE_UNAVAILABLE = 503;
/**
* Status code (504) indicating that the server did not receive
* a timely response from the upstream server while acting as
* a gateway or proxy.
*/
public static final int SC_GATEWAY_TIMEOUT = 504;
/**
* Status code (505) indicating that the server does not support
* or refuses to support the HTTP protocol version that was used
* in the request message.
*/
public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
2.常见应用
- 向浏览器输出消息 resp.getWriter().print(username +":"+password);
- 下载文件
- 要获取下载文件的路径
- 下载的文件名是啥
- 设置想办法让浏览器能够支持下载我们需要的东西
- 获取下载文件的输入流
- 创建缓冲区
- 获取OutputStream对象
- 将FileOutputStream流写入到buffer缓冲区
- 使用OutputStream将缓冲区中的数据输出到客户端
public class FileServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取文件的相对路径
String path = this.getServletContext().getRealPath("/WEB-INF/classes/image-20201225111804440.png");
System.out.println("下载文件的地址："+ path);
//下载的文件名是啥
String filename = path.substring(path.lastIndexOf("\\")+1);//获取文件名称，在转化为子串
//response.setHeader告诉浏览器以什么方式打开
//假如文件名称是中文则要使用 URLEncoder.encode()编码
//否则直接使用response.setHeader("content-disposition", "attachment;filename=" + filename);即可
resp.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(filename, "UTF-8"));
InputStream in = null ;
OutputStream out = null ;
try {
in = new FileInputStream(path); //获取文件的流
int len = 0;
byte buf[] = new byte[1024];//缓存作用
out = resp.getOutputStream();//输出流
while( (len = in.read(buf)) > 0 ){ //切忌这后面不能加 分号 ”;“
out.write(buf, 0, len);//向客户端输出，实际是把数据存放在response中，然后web服务器再去response中读取
}
}finally {
if(in!=null) {
try{
in.close();
}catch(IOException e){
e.printStackTrace();
}
}
if(out!=null) {
try{
out.close();
}catch(IOException e){
e.printStackTrace();
}
}
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
3.验证码功能
验证怎么来的？
- 前端实现
- 后端实现，需要用到java的图片类，生产一个图片
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//如何让浏览器3秒自动刷新一次
resp.setHeader("refresh","3");
//在内存占用创建一个图片
BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D g = (Graphics2D) image.getGraphics();//笔
//设置背景颜色
g.setColor(Color.white);
g.fillRect(0,0,80,20);
//给图片写数据
g.setColor(Color.red);
g.setFont(new Font(null,Font.BOLD,20));
g.drawString(makeNum(),0,20);
//告诉浏览器，这个请求用图片方式打开
resp.setContentType("image/jpeg");
//网站存在缓存，不让浏览器缓存
resp.setDateHeader("expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Pragma","no-cache");
//图片写给浏览器
ImageIO.write(image,"jpg",resp.getOutputStream());
}
//生成随机数
private String makeNum(){
Random random = new Random();
//String num = String.valueOf(random.nextInt(9999999));
String num = random.nextInt(9999999)+"";
StringBuffer sb = new StringBuffer();
for (int i = 0; i < 7-num.length(); i++) {
sb.append("0");
}
num = sb.toString()+num;
return num;
}
@Override
protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
4.实现重定向
B一个web资源收到客户端A请求后，B他会通知A客户端去访问另外一个web资源C,这个过程叫重定向。
常见场景：用户登录
public void sendRedirect(String location) throws IOException;
测试：
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setHeader("Location","/r/img");
resp.setStatus(302);
resp.sendRedirect("/r/img"); //重定向
}
面试题：请你聊聊重定向和转发的区别？
相同点 页面都是实现跳转
不同点 请求转发的时候，url不会产生变化307 重定向时候，url地址栏会发生变化302
简单请求响应
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入这个请求");
//处理请求
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username +":"+ password);
//重定向
resp.sendRedirect("/r/success.jsp");
}
<%--这里提交的路径，需要寻找到项目的路径--%>
<%--${pageContext.request.contextPath} 项目路径--%>
<form action="${pageContext.request.contextPath}/login" method="get">
用户名：<input type="text" name="username"><br>
密码： <input type="password" name="password"><br>
<input type="submit">
</form>
6.6 HttpServletRequest
- 获取前端传递过来的参数
req.getParameter("username"); //String
req.getParameterValues() //String[]
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入这个请求");
//编码问题
req.setCharacterEncoding("utf-8");
resp.setCharacterEncoding("utf-8");
//处理请求
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username +":"+ password);
//重定向
//resp.sendRedirect("/r/success.jsp");
//转发
req.getRequestDispatcher("success.jsp").forward(req,resp);
}
标签：code,JavaWeb,int,resp,static,20210121,SC,Servlet,public 来源： https://blog.csdn.net/qq_41096598/article/details/112968482