servlet知识点
Servlet
- 1.简介
- 2.HelloServlet
- 3.Servlet原理
- 4.Mapping问题
- 5.ServletContext
-
- 1.共享数据
- 2.获取初始化参数
- 3.请求转发
- 4.读取资源文件
- 6.HttpServletRequest
-
- 1.获取前端传递的参数
- 7.HttpServletResponse
-
- 1.简单分类
- 2.下载文件
- 3.验证码功能
- 4.实现重定向
1.简介
servlet接口sun公司有两个默认的实现类：HttpServlet,GenericServlet
- 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servlet程序，只需要完成两小步：
- 编写一个类，实现servlet接口
- 部署到web服务器中
把实现了Servlet接口的Java程序叫做，Servlet
2.HelloServlet
-
构建一个Maven项目，删除里面的src目录，在项目中建立module；
-
关于Maven父子工程的理解：
父项目中会有
<modules> <module>servlet-01module> modules>子项目会有
<parent> <artifactId>javaweb-02-servletartifactId> <groupId>org.examplegroupId> <version>1.0-SNAPSHOTversion> 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
webapp
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
web-app>
-
将Maven的结构搭建完整
-
web项目依赖
servlet和jsppom.xml
<dependency> <groupId>javax.servlet.jspgroupId> <artifactId>javax.servlet.jsp-apiartifactId> <version>2.3.3version> dependency> <dependency> <groupId>javax.servletgroupId> <artifactId>javax.servlet-apiartifactId> <version>4.0.1version> dependency> -
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 { // 由于get或者post只是请求实现的不同方式，可以互相调用，业务逻辑一样 @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { PrintWriter writer = resp.getWriter(); //响应流 writer.println("hello,Servlet"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); } }
-
-
编写Servlet的映射
为什么需要映射：我们写的是java程序，但是通过浏览器访问，而浏览器需要连接web服务器，所以我们需要再web服务中注册我们写的Servlet，还需要给他一个浏览器可以访问的路径；
<servlet> <servlet-name>helloservlet-name> <servlet-class>com.wan.servlet.HelloServletservlet-class> servlet> <servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>hellourl-pattern> servlet-mapping> -
配置Tomcat
注意：配置项目发布的路径就可以了
3.Servlet原理
servlet是有web服务器调用，web服务器在收到浏览器请求后会提供响应；
4.Mapping问题
-
一个Servlet可以指定一个映射路径
<servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>/hellourl-pattern> servlet-mapping> -
一个Servlet可以指定多个映射路径
<servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>/hello1url-pattern> servlet-mapping> <servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>/hello2url-pattern> servlet-mapping> <servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>/hello3url-pattern> servlet-mapping> -
一个Servlet可以指定通用映射路径
<servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>/hello/*url-pattern> servlet-mapping> -
指定一些后缀或者前缀等等。。。
<servlet-mapping> <servlet-name>helloservlet-name> <url-pattern>*.dourl-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请求路径；
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；
1.共享数据
eg:
添加属性
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String username = "张三";
context.setAttribute("username", username); //键值对形式输入
}
获取属性：
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String name = (String) context.getAttribute("username");
resp.setCharacterEncoding("utf-8");
resp.setContentType("text/html");
resp.getWriter().println("姓名"+name);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doGet(req, resp);
}
配置
<servlet>
<servlet-name>helloservlet-name>
<servlet-class>com.wan.servlet.HelloServletservlet-class>
servlet>
<servlet-mapping>
<servlet-name>helloservlet-name>
<url-pattern>/hellourl-pattern>
servlet-mapping>
<servlet>
<servlet-name>getcservlet-name>
<servlet-class>com.wan.servlet.GetServletContextservlet-class>
servlet>
<servlet-mapping>
<servlet-name>getcservlet-name>
<url-pattern>/getcurl-pattern>
servlet-mapping>
2.获取初始化参数
xml中设置初始化参数
eg：数据库参数
<context-param>
<param-name>urlparam-name>
<param-value>jdbc:mysql:http://localhost:3306/mybatisparam-value>
context-param>
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String url = this.getServletContext().getInitParameter("url");
resp.getWriter().println(url);
}
3.请求转发
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
System.out.println("进入了RequestD");
context.getRequestDispatcher("/getp").forward(req, resp); //调用forward实现请求转发；
}
4.读取资源文件
Properties
-
在java目录下新建properties(注意配置pom.xml文件，不然可能maven导出不了properties文件)
pom.xml配置文件
<build>
<resources>
<resource>
<directory>src/main/resourcesdirectory>
<includes>
<includes>**/*.propertiesincludes>
<includes>**/*.xmlincludes>
includes>
<filtering>falsefiltering>
resource>
<resource>
<directory>src/main/javadirectory>
<includes>
<include>**/*.propertiesinclude>
<include>**/*.xmlinclude>
includes>
<filtering>falsefiltering>
resource>
resources>
build>
- 在resource下新建properties
需要一个文件流；
username = root
password = 123456
java代码
public class PropertiesServlet extends HelloServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream is = getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
Properties prop = new Properties();
prop.load(is);
String usr = prop.getProperty("username");
String pwd = prop.getProperty("password");
resp.getWriter().println(usr+":"+pwd);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doGet(req,resp);
}
}
web.xml
<servlet>
<servlet-name>psservlet-name>
<servlet-class>com.wan.servlet.PropertiesServletservlet-class>
servlet>
<servlet-mapping>
<servlet-name>psservlet-name>
<url-pattern>/psurl-pattern>
servlet-mapping>
访问测试
6.HttpServletRequest
HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，通过HttpServletRequest中的方法，获得客户端的所有信息；
1.获取前端传递的参数
index.jsp主页
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@page isELIgnored="false"%>
登录
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("hello");
req.setCharacterEncoding("utf-8");
resp.setCharacterEncoding("utf-8");
String password = req.getParameter("password");
String username = req.getParameter("username");
String[] hobbys = req.getParameterValues("hobbys");
System.out.println("==========================");
System.out.println("用户名："+username);
System.out.println("密码:"+password);
System.out.println("爱好："+ Arrays.toString(hobbys));
System.out.println("==========================");
//请求转发
req.getRequestDispatcher("success.jsp").forward(req,resp);
}
7.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;
- 如果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
-
ServletOutputStream getOutputStream() throws IOException; PrintWriter getWriter() throws IOException;
负责向浏览器发送响应头的方法
void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
void setDateHeader(String var1, long var2);
void addDateHeader(String var1, long var2);
void setHeader(String var1, String var2);
void addHeader(String var1, String var2);
void setIntHeader(String var1, int var2);
void addIntHeader(String var1, int var2);
void setStatus(int var1);
响应的状态码
int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
记大概的就够了
200：请求响应成功
3**：请求重定向
404：找不到资源
- 资源不存在
5XX：服务器代码错误 500 502：网关错误
2.下载文件
-
向浏览器输出消息
-
下载文件
1.要获取下载文件的路径
2.下载的文件名
3.设置办法让浏览器能够支持下载我们需要的东西
4.获取下载文件的输入流
5.创建缓冲区
6.获取outputstream对象
7.将FileOut普通Stream流写入到buffer缓冲区
8.使用OutPutStream将缓冲区中的数据输出到客户端
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 1.要获取下载文件的路径
String realPath = "D:\\code\\javaweb\\javaweb-02-servlet\\response\\src\\main\\resources\\腾讯qqicon.png";
//String realPath = this.getServletContext().getRealPath("/腾讯qqicon.png"); 这样找的路径不对
System.out.println("下载的文件路径："+realPath);
// 2.下载的文件名
String filename = realPath.substring(realPath.lastIndexOf("\\") + 1);
System.out.println("filename="+filename);
// 3.设置办法让浏览器能够支持下载我们需要的东西，中文文件名URLEncoder.encode编码，否则有可能乱码
resp.setHeader("Content-disposition","attachment;filename="+ URLEncoder.encode(filename,"utf-8"));
// 4.获取下载文件的输入流
FileInputStream in = new FileInputStream(realPath);
// 5.创建缓冲区
int len = 0;
byte[] buffer = new byte[1024];
// 6.获取outputstream对象
ServletOutputStream out = resp.getOutputStream();
// 7.将FileOutStream流写入到buffer缓冲区
while((len = in.read(buffer))!=-1){
// 8.使用OutPutStream将缓冲区中的数据输出到客户端
out.write(buffer,0,len);
}
in.close();
out.close();
}
3.验证码功能
验证码怎么来？
- 前端实现
- 后端实现，用java的图片类，生产一个图片
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//浏览器3秒刷新一次
resp.setHeader("refresh","3");
//在内存中创建一个图片
BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
Graphics2D g = (Graphics2D) image.getGraphics();
//设置图片背景颜色
g.setColor(Color.white);
g.fillRect(0,0,80,20);
g.setColor(Color.BLUE);
g.setFont(new Font(null,Font.BOLD,20));
g.drawString(makeNum(),0,20);
//告诉浏览器，这个请求用图片的方式打开
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");
//把图片返回给浏览器
ImageIO.write(image, "jpg", resp.getOutputStream());
}
/**
* 生成随机数
* @return
*/
private String makeNum(){
Random random = new Random();
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;
}
4.实现重定向
一个web资源收到客户端请求后，他会通知客户端去访问另一个web资源C，这个过程叫重定向
void sendRedirect(String var1) throws IOException;
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/*
resp.setHeader("Location","/response_Web_exploded/image");
resp.setStatus(302);
*/
resp.sendRedirect("/response_Web_exploded/image");
}
重定向与转发的区别：
相同点：
- 页面会跳转
不同点：
- 请求转发的时候，url会发生变化 307
- 重定向的时候，url后发生变化 302
案例
需求：登录完成后重定向
RequestTest.java
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入requestTest类！");
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username+":"+password);
resp.sendRedirect("/response_Web_exploded/success.jsp");
}
web.xml
<servlet>
<servlet-name>requestservlet-name>
<servlet-class>RequestTestservlet-class>
servlet>
<servlet-mapping>
<servlet-name>requestservlet-name>
<url-pattern>/loginurl-pattern>
servlet-mapping>
index.jsp
Hello World!
<%@ page pageEncoding="UTF-8" %>
success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
success
congratulation