1、helloservlet
在浏览器中输出 hello servlet!
1.1、创建一个maven项目,连接Tomcat
public class HelloServlet extends HttpServlet {
//Art+Ins
//由于get或者post只是请求实现的不同的方式,可以相互调用,业务逻辑都一样
@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 {
doGet(req,resp);
}
}
1.2、在web.xml文件中写添加映射
<?xml version="1.0" encoding="UTF-8"?>
<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">
<!--注册servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.feng.servlet.HelloServlet</servlet-class>
</servlet>
<!--mapping:映射-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
</web-app>
为什么需要映射:我们写的是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,还需给他一个浏览器能够访问的路径
如果项目没有web,直接项目右键添加即可!
2、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;
2.1、共享数据
public class SetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//this.getInitParameter();初始化参数
//this.getServletConfig();Servlet配置
//this.getServletContext();Servlet上下文
ServletContext context = this.getServletContext();
String name = "bitwind";
//将一个数据保存在了ServletContext中
context.setAttribute("username",name);//setAttribute : 设置属性
}
@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 {
//获取ServletContext中的值
ServletContext context = this.getServletContext();
String name = (String) context.getAttribute("username");
resp.getWriter().println("name = "+name);
System.out.println(name);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
添加映射
启动Tomcat,访问!
注意:要先访问GetServlet类,否则name=null,要先存进ServletContext,才有得拿!
2.2、获取初始化参数
public class GetInitParameter extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
//this.getInitParameter();初始化参数
//this.getServletConfig();Servlet配置
//this.getServletContext();Servlet上下文
ServletContext context = this.getServletContext();
String name = context.getInitParameter("Tom");
resp.getWriter().println(name);
System.out.println(name);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
在web.xml中设置初始化参数
<!--初始化参数-->
<context-param>
<param-name>Tom</param-name>
<param-value>这是javaweb,这是servlet,这是初始化参数!</param-value>
</context-param>
添加映射
启动Tomcat,访问!
2.3、请求转发
public class GetRequestDispatcher extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
System.out.println("这是GetRequestDispatcher!!!");
RequestDispatcher dispatcher = context.getRequestDispatcher("/init");//这是web设置的url路径
dispatcher.forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
添加映射
启动Tomcat,访问!
2.4、读取资源文件
target*是用来存放项目构建后的文件和目录、jar包、war包、编译的class*文件
Properties
- 在java目录下新建properties文件
- 在resources目录新建properties文件
username=张三
password=123456
发现:都被打包到了同一个路径下:classes,我们俗称这个路径为classpath;
public class GetProperties extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
//第一条“/”不能省略,代表真当前web项目
InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
Properties prop = new Properties();
prop.load(is);//获取文件流
String user = prop.getProperty("username");
String pwd = prop.getProperty("password");
resp.getWriter().print(user+":"+pwd);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
注意:"/WEB-INF/classes/db.properties"这是target 下的项目同名的目录路径!
添加映射
启动Tomcat,访问!
注意:要用maven模板新建的项目,这个target 目录下才有项目同名的包!
3、HttpServletRespouse
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
3.1、下载文件
- 要获取下载文件的路径
- 下载的文件名是什么?
- 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buffer缓冲区
- 使用OutputStream将缓冲区中的数据输出到客户端!
response下载文件
public class HSResponse extends HelloServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String realPath = "文件路径\\文件名.文件类型";
//2. 下载的文件名是什么?
String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
FileInputStream fileInputStream = new FileInputStream(realPath);
int len = 0;
byte[] buffer = new byte[1024];
ServletOutputStream outputStream = resp.getOutputStream();
while ((len = fileInputStream.read(buffer)) > 0){
outputStream.write(buffer,0,len);
}
fileInputStream.close();
outputStream.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
添加映射
启动Tomcat,访问!
3.2、实现重定向
一个web资源收到客户端请求后,它会通知客户端去访问另一个web资源,这个过程叫重定向:
void sendRedirect(java.lang.String s) throws java.io.IOException;
public class Send extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.sendRedirect("/init");//路径发生变化
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
4、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HttpServlet,通过这个HttpServlet的方法,获得客户端的所有信息;
4.1、获取前端传递的参数和请求转发
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>HSRequest</title>
</head>
<body>
<div>
<form action="${pageContext.request.contextPath}/request" method="post">
用户名:<input type="text" name="username"><br>
密码:<input type="password" name="password"><br>
爱好:
<input type="checkbox" name="hobbys" value="java">java
<input type="checkbox" name="hobbys" value="JavaScript">JavaScript
<input type="checkbox" name="hobbys" value="Oracle">Oracle
<input type="checkbox" name="hobbys" value="Python">Python
<br>
<input type="submit">
</form>
</div>
</body>
</html>
public class HSRequest extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
String password = req.getParameter("password");
String[] hobbys = req.getParameterValues("hobbys");
System.out.println(username+"\t"+password+"\t"+ Arrays.toString(hobbys));
req.getRequestDispatcher("/success.jsp").forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>成功页面</title>
</head>
<body>
<h1>登录成功</h1>
<a href="${pageContext.request.contextPath}/index.jsp">首页</a>
</body>
</html>