沉浸式求职学习
Servlet
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Servlet程序，只需要完成两个小步骤：
- 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
2.HelloServlet
Serlvet接口Sun公司有两个默认的实现类：HttpServlet，GenericServlet。
接下来我们编写一个Servlet程序：
-
编写一个普通类。
-
实现Servlet接口，这里我们直接继承HttpServlet
java
package com.hh.servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class helloServlet extends HttpServlet {
// 由于get或者Post只是请求实现的不同方式，可以相互调用，业务逻辑都一样
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入doGet方法");
PrintWriter writer = resp.getWriter(); //响应流
// ServletOutputStream outputStream = resp.getOutputStream();
writer.print("hello,servlet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}然后编写servlet映射：
xml
<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"
metadata-complete="true">
<!-- 注册Servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.hh.servlet.helloServlet</servlet-class>
</servlet>
<!-- Servlet请求路径-->
<!-- localhost:8080/s3/hello/hello-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello/hello</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<!-- 注册404-->
<!-- <servlet>-->
<!-- <servlet-name>error</servlet-name>-->
<!-- <servlet-class>com.hh.servlet.errorServlet</servlet-class>-->
<!-- </servlet>-->
<!-- <servlet-mapping>-->
<!-- <servlet-name>error</servlet-name>-->
<!-- <url-pattern>/*</url-pattern>-->
<!-- </servlet-mapping>-->
</web-app>运行Tomcat：
Servlet原理
首先浏览器发送Http请求给web容器（可以理解为Tomcat）然后Requset通过Servlet去调用Service方法，产生一个Response，这个请求赋给响应体，然后在给Web容器。其中Servlet这里是我们自己取编写的实现类，并且重写这些方法，比如接受并处理请求，且给出响应的信息。
3.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；
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；
java
package com.hh.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class HelloServlet 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
// Web容器启动的时候，会为每个WEB程序创建一个对应的ServletContext对象，代表当前WEB应用
ServletContext context = this.getServletContext();
String username = "哈哈哈哈哈";
context.setAttribute("username",username); // 将一个数据保存在context中
System.out.println("hello");
}
}首先先通过setAttribute把数据保存在context中
接着从另外一个Servlet中取数据：
java
package com.hh.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
String username = (String) servletContext.getAttribute("username");
//
resp.setCharacterEncoding("utf-8");
resp.setContentType("text/html");
resp.getWriter().print("名字"+username);
}
}
结果:
拿到初始化信息
java
package com.hh.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Properties;
public class servlet_test3 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
String url = servletContext.getInitParameter("url");
resp.getWriter().print(url);
Properties properties = new Properties();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doPost(req, resp);
}
}
结果：
请求转发
java
package com.hh.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class servlet_test4 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入了test4");
ServletContext servletContext = this.getServletContext();
servletContext.getRequestDispatcher("/gp").forward(req,resp); //转发的请求路径
}
}
结果：
读取资源文件
Properties
- 在java目录下新建properties
- 在resources目录下新建properties
java
package com.hh.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
public class PropertiesServlet extends HelloServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream resourceAsStream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/hh/servlet/aa.properties");// /代表当前项目位置
Properties properties = new Properties();
properties.load(resourceAsStream);
String username = properties.getProperty("username");
String password= properties.getProperty("password");
resp.getWriter().print(username+":"+password);
}
}
结果：
