Servlet
Servlet简介
- Servlet就是sun公司开发动态web的一门技术
- sun公司在这些API中提供了一个接口叫做: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
Hello Servlet
Servlet接口Sun公司有两个默认的实现类:HttpServlet,GenericServlet
构建一个普通的Maven项目
- 删掉里面的src项目
- 创建servlet子项目
关于Maven父子工程的理解
父项目中会有
<modules>
<module>servlet-01</module>
</modules>
子项目中会有
<parent>
<artifactId>javaweb-02-servleb</artifactId>
<groupId>com.binzaza</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
父项目中的jar包,子项目可以直接使用
son extends father
Maven环境优化
- 更新web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee
https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0"
metadata-complete="true">
</web-app>
- 创建java、resources文件夹(maven的结构搭建完整)
编写一个Serlet程序
- 编写一个普通类
../servlet-01/src/main/java/com.binzaza.servlet
HelloServlet.java
public class HelloServlet extends HttpServlet {
}
- 实现Servlet接口,这里我们直接继承HttpServlet
public class HelloServlet extends HttpServlet {
// 重新方法 Ctrl + O
// 有GET、POST 只是请求实现的不同方式,可以相互调用,因为业务逻辑都一样
@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 Servlet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
编写Servlet的映射
为什么需要映射:我们写的是java程序,但是需要通过浏览器访问,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,还需要给它一个浏览器能够访问的路径
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee
https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0"
metadata-complete="true">
<!--注册servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.binzaza.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>
</web-app>
配置tomcat
启动测试
默认:http://localhost:8080/s1/
访问映射路径:http://localhost:8080/s1/hello
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,
Mapping 问题
web.xml
- 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>
- 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>/hello1</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>
- 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>
- 默认请求路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
- 指定一些后缀或者前缀等等
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>*.binzaza</url-pattern>
</servlet-mapping>
- 优先级问题
定义404
创建ErrorServlet.java
public class ErrorServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setCharacterEncoding("utf-8");
resp.setContentType("text/html");
PrintWriter writer = resp.getWriter();
writer.print("<h1>我的404</h1>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
配置映射
web.xml
<!--404-->
<servlet>
<servlet-name>error</servlet-name>
<servlet-class>com.binzaza.servlet.ErrorServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>error</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
指定了固有的映射路径优先级最高,如果找不到就会找默认的处理请求
ServletContext对象
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
我在servlet中保存的数据,可以在另外一个servlet中拿到
在父项目javaweb-02-servlet下
父项目
pom.xml
<modules>
<module>servlet-01</module>
<module>servlet-02</module>
</modules>
子项目
pom.xml
<parent>
<artifactId>javaweb-02-servleb</artifactId>
<groupId>com.binzaza</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
更新web.xml文件
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee
https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0"
metadata-complete="true">
</web-app>
优化maven结构
建包,创建类
servlet-02/src/main/java/com.binzaz.servlet
创建HelloServlet.java
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 = "冰渣渣";
context.setAttribute("username",username); // 将一个数据保存在了ServletContext中,名字为:username,值为username
}
}
创建GetServlet.java
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: "+username);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
配置映射web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee
https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0"
metadata-complete="true">
<!--注册servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.binzaza.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.binzaza.servlet.GetServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>getc</servlet-name>
<url-pattern>/getc</url-pattern>
</servlet-mapping>
</web-app>
启动tomcat
先访问:http://localhost:8080/s2/hello
再打开:http://localhost:8080/s2/getc
ServletContext应用
获取初始化参数
web.xml配置参数以及路由
<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.binzaza.servlet.ServletDemo03</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>gp</servlet-name>
<url-pattern>/gp</url-pattern>
</servlet-mapping>
创建ServletDemo03.java
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);
}
}
启动tomcat
访问:http://localhost:8080/s2/gp
Ctrl + [ 向前缩进, Ctrl + ] 向后缩进。
请求转发
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sd4页面");
// RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp"); // 转发请求路径
// 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);
}
}
<servlet>
<servlet-name>sd4</servlet-name>
<servlet-class>com.binzaza.servlet.ServletDemo04</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>sd4</servlet-name>
<url-pattern>/sd4</url-pattern>
</servlet-mapping>
读取资源文件
maven配置pom.xml的时候可能会出现的一个问题:资源可能无法导出,这时候需要在pom.xml的build标签添加导出路径
<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>
Properties
- 在java目录下新建properties
- 在resources目录下新建properties
发现:都被打包到了同一个路径下:classes,我们俗称这个路径为lasspath
在resource目录下建db.properties文件
username=root
password=123456
创建文件ServletDemo05.java
public class ServletDemo05 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
// InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/binzaza/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);
}
}
启动tomcat
访问:http://localhost:8080/s2/sd5