Web开发之Tomcat&Servlet

时间:2023-03-08 18:59:00
Web开发之Tomcat&Servlet

<!doctype html>01 - JavaEE - Tomcat&Servlet

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Web开发之Tomcat&Servlet

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1. web相关概念回顾
2. web服务器软件:Tomcat
3. Servlet入门学习

web相关概念回顾

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1. 软件架构
1. C/S:客户端/服务器端
2. B/S:浏览器/服务器端
2. 资源分类
1. 静态资源:所有用户访问后,得到的结果都是一样的,称为静态资源.静态资源可以直接被浏览器解析
* 如: html,css,JavaScript
2. 动态资源:每个用户访问相同资源后,得到的结果可能不一样。称为动态资源。动态资源被访问后,需要先转换为静态资源,在返回给浏览器
* 如:servlet/jsp,php,asp....
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3. 网络通信三要素
1. IP:电子设备(计算机)在网络中的唯一标识。
2. 端口:应用程序在计算机中的唯一标识。 0~65536
3. 传输协议:规定了数据传输的规则
1. 基础协议:
1. tcp:安全协议,三次握手。 速度稍慢
2. udp:不安全协议。 速度快

web服务器软件:

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* 服务器:安装了服务器软件的计算机
* 服务器软件:接收用户的请求,处理请求,做出响应
* web服务器软件:接收用户的请求,处理请求,做出响应。
* 在web服务器软件中,可以部署web项目,让用户通过浏览器来访问这些项目
* web容器
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* 常见的java相关的web服务器软件:
* webLogic:oracle公司,大型的JavaEE服务器,支持所有的JavaEE规范,收费的。
* webSphere:IBM公司,大型的JavaEE服务器,支持所有的JavaEE规范,收费的。
* JBOSS:JBOSS公司的,大型的JavaEE服务器,支持所有的JavaEE规范,收费的。
* Tomcat:Apache基金组织,中小型的JavaEE服务器,仅仅支持少量的JavaEE规范servlet/jsp。开源的,免费的。
* JavaEE: 使用Java开发Web应用的各种规则和规范的总和
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* Tomcat:web服务器软件
1. 下载:http://tomcat.apache.org/
2. 安装:解压压缩包即可。
* 注意:安装目录建议不要有中文和空格
3. 卸载:删除目录就行了
4. 启动:
* bin/startup.bat ,双击运行该文件即可
* 访问:浏览器输入:http://localhost:8080 回车访问自己
  http://别人的ip:8080 访问别人

* 可能遇到的问题:
1. 黑窗口一闪而过:
* 原因: 没有正确配置JAVA_HOME环境变量
* 解决方案:正确配置JAVA_HOME环境变量
2. 启动报错:
1. 暴力:找到占用的端口号,并且找到对应的进程,杀死该进程
* netstat -ano
2. 温柔:修改自身的端口号
* conf/server.xml
* <Connector port="8888" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8445" />
* 一般会将tomcat的默认端口号修改为80。80端口号是http协议的默认端口号。
* 好处:在访问时,就不用输入端口号
5. 关闭:
1. 正常关闭:
* bin/shutdown.bat
* ctrl+c
2. 强制关闭:
* 点击启动窗口的×
6. 配置:
* 部署项目的方式:
1. 直接将项目放到webapps目录下即可。
* /hello:项目的访问路径-->虚拟目录
* 简化部署:将项目打成一个war包,再将war包放置到webapps目录下。
* war包会自动解压缩
2. 配置conf/server.xml文件
在<Host>标签体中配置
<Context docBase="D:\hello" path="/hehe" />
* docBase:项目存放的路径
* path:虚拟目录
3. 在conf\Catalina\localhost创建任意名称的xml文件。在文件中编写
<Context docBase="D:\hello" />
* 虚拟目录:xml文件的名称

* 静态项目和动态项目:
* 目录结构
* java动态项目的目录结构:
-- 项目的根目录
-- WEB-INF目录:
-- web.xml:web项目的核心配置文件
-- classes目录:放置字节码文件的目录
-- lib目录:放置依赖的jar包
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* 将Tomcat集成到Eclipse中,并且创建JavaEE的项目,部署项目。

Servlet: server applet

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* 概念:运行在服务器端的小程序
* Servlet就是一个接口,定义了Java类被浏览器访问到(tomcat识别)的规则。
* 将来我们自定义一个类,实现Servlet接口,复写方法。
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* 快速入门:
1. 创建JavaEE项目
2. 定义一个类,实现Servlet接口
3. 实现接口中的抽象方法
4. 配置Servlet
* 执行原理:
1. 当服务器接受到客户端浏览器的请求后,会解析请求URL路径,获取访问的Servlet的资源路径
2. 查找web.xml文件,是否有对应的<url-pattern>标签体内容。
3. 如果有,则在找到对应的<servlet-class>全类名
4. tomcat会将字节码文件加载进内存,并且创建其对象
5. 调用其方法
* Servlet中的生命周期方法:
1. 被创建:执行init方法,只执行一次
* Servlet什么时候被创建?
* 默认情况下,第一次被访问时,Servlet被创建
* 可以配置执行Servlet的创建时机。
* 在<servlet>标签下配置
1. 第一次被访问时,创建
                * <load-on-startup>的值为负数
            2. 在服务器启动时,创建
                * <load-on-startup>的值为0或正整数
* Servlet的init方法,只执行一次,说明一个Servlet在内存中只存在一个对象,Servlet是单例的
* 多个用户同时访问时,可能存在线程安全问题。
* 解决:尽量不要在Servlet中定义成员变量。即使定义了成员变量,也不要对修改值
2. 提供服务:执行service方法,执行多次
* 每次访问Servlet时,Service方法都会被调用一次。
3. 被销毁:执行destroy方法,只执行一次
* Servlet被销毁时执行。服务器关闭时,Servlet被销毁
* 只有服务器正常关闭时,才会执行destroy方法。
* destroy方法在Servlet被销毁之前执行,一般用于释放资源
* Servlet3.0:
* 好处:
* 支持注解配置。可以不需要web.xml了。
* 步骤:
1. 创建JavaEE项目,选择Servlet的版本3.0以上,可以不创建web.xml
2. 定义一个类,实现Servlet接口
3. 复写方法
4. 在类上使用@WebServlet注解,进行配置
* @WebServlet("资源路径")