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
(1)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面建立Moudel;这个空的工程就是Maven主工程;
举例:先创建一个普通的Maven项目,命名为javaweb-02-servlet,再删掉里面的src目录,增加dependencipes,最后在此项目里建立一个Moudel,命名为servlet-01
建立Moudel
(2)关于Maven父子工程的理解
父项目中会有
<modules>
<module>servlet-01</module>
</modules>
子项目会有
<parent>
<artifactId>javaweb-02-servlet</artifactId>
<groupId>com.kuang</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
(3)Maven环境优化
- 修改web.xml为最新的
- 将maven的结构搭建完整
在main目录下创建java和resources两个包,并进行标记
(4)编写一个Servlet程序
①编写一个普通类
②实现Servlet接口,这里我们直接继承HttpServlet
package com.zz.servlet;
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.io.PrintWriter;
public class HelloServlet extends HttpServlet {
//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 {
//ServletOutputStream outputStream = resp.getOutputStream();
PrintWriter writer = resp.getWriter(); //响应流
writer.print("Hello,Serlvet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
(5)编写Servlet的映射
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服务中注册我们写的Servlet,还需给他一个浏览器能够访问的路径;
<!--注册Servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.zz.servlet.HelloServlet</servlet-class>
</servlet>
<!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
(6)配置Tomcat
注意:配置项目发布的路径就可以了
(7)启动测试,OK!
点击右上方的启动按钮,运行成功后会生成一个名为target文件夹
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:
4. Mapping问题
(1)一个Servlet可以指定一个映射路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
(2)一个Servlet可以指定多个映射路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello2</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello3</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello4</url-pattern>
</servlet-mapping>
(3)一个Servlet可以指定通用映射路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello/*</url-pattern>
</servlet-mapping>
(4)默认请求路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
(5)指定一些后缀或者前缀等
<!--可以自定义后缀实现请求映射
注意点*前面不能加项目映射的路径
hello/sajdlkajda.zz 也可以
-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>*.zz</url-pattern>
</servlet-mapping>
注意:点*前面不能加项目映射的路径,即去掉点 * 前面的 / 符号
(6)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;
<!--注册Servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.zz.servlet.HelloServlet</servlet-class>
</servlet>
<!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<!--注册Servlet-->
<servlet>
<servlet-name>error</servlet-name>
<servlet-class>com.zz.servlet.ErrorServlet</servlet-class>
</servlet>
<!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>error</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
由上图可知,hello也属于/* ,但输入hello,进入的是HelloServlet
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,具体有如下应用
(1)共享数据
我在这个Servlet中保存的数据,可以在另外一个servlet中拿到;
HelloServlet 中的代码:
package com.zz.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
ServletContext context = this.getServletContext();
String username = "大佬"; //数据
context.setAttribute("username", username);
//将一个数据保存在了ServletContext中,名字为:username 。值 username
}
}
GetServlet 中的代码:
package com.zz.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 context = this.getServletContext();
String username = (String) context.getAttribute("username");
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
resp.getWriter().print("名字为"+username);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
web.xml 中的代码:
<?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"
metadata-complete="true">
<!--注册Servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.zz.servlet.HelloServlet</servlet-class>
</servlet>
<!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>getc</servlet-name>
<servlet-class>com.zz.servlet.GetServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>getc</servlet-name>
<url-pattern>/getc</url-pattern>
</servlet-mapping>
</web-app>
测试访问结果:
- 直接输入getc
- 先输入hello ,再输入getc
(2)获取初始化参数
创建ServletDemo03
package com.zz.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 ServletDemo03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String url = context.getInitParameter("url");
resp.getWriter().print(url);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
在web.xml 中添加如下配置:
<!--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>
<servlet>
<servlet-name>gp</servlet-name>
<servlet-class>com.zz.servlet.ServletDemo03</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>gp</servlet-name>
<url-pattern>/gp</url-pattern>
</servlet-mapping>
测试访问结果:
(3)请求转发
创建ServletDemo04
package com.zz.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 ServletDemo04 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
System.out.println("进入了ServletDemo04");
//RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp"); //转发的请求路径
//requestDispatcher.forward(req,resp); //调用forward实现请求转发;
context.getRequestDispatcher("/gp").forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
在web.xml 中添加如下配置:
<servlet>
<servlet-name>sd4</servlet-name>
<servlet-class>com.zz.servlet.ServletDemo04</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>sd4</servlet-name>
<url-pattern>/sd4</url-pattern>
</servlet-mapping>
测试访问结果:
可以看出,访问到的是gp的界面,但访问地址并不会发生变化
(4)读取资源文件
Properties
- 在java目录下新建aa.properties
username=root123
password=hahaha123 - 在resources目录下新建db.properties
username=root
password=123456
点击Tomcat运行后,发现db.properties在目录下,但aa.properties 不在
解决方法:在当前pom.xml文件的build中配置resources,来防止我们资源导出失败的问题
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>
再次点击Tomcat运行后发现:都被打包到了同一个路径下:classes,我们俗称这个路径为classpath:
- 创建ServletDemo05,读取资源文件aa.properties
思路:需要一个文件流
package com.zz.servlet;
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.io.InputStream;
import java.util.Properties;
public class ServletDemo05 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/zz/servlet/aa.properties");
Properties prop = new Properties();
prop.load(is);
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);
}
}
- 再在web.xml 中添加如下配置:
<servlet>
<servlet-name>sd5</servlet-name>
<servlet-class>com.zz.servlet.ServletDemo05</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>sd5</servlet-name>
<url-pattern>/sd5</url-pattern>
</servlet-mapping>
测试访问结果:
读取资源文件db.properties 与上同理。