servlet
一、使用
1.建立一个普通的maven项目,不加模板的项目。删除src文件这样就可以在这个项目下建立很多的子项目
2.建立一个子项目,子项目的pom.xml就会有父项目的信息
<parent>
<artifactId>Saxon_01_servlet</artifactId>
<groupId>org.example</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
父项目中就会添加一个子项目信息
<modules>
<module>Saxon_Servlet_Son_01</module>
</modules>
建项目吗?父子局
son extends father
3.环境优化
- 配置web.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">
</web-app>
- 优化结构,加上一些该加上的文件夹 Java ,resources
4.编写第一个servlet程序
sun公司的servlet的实现类:HttpServlet,GenericServlet
- 先创建一个普通的类
- 这个类去继承servlet的实现类
//继承HttpServlet
import javax.servlet.http.HttpServlet;
public class HelloServlet extends HttpServlet {
}
//HttpServlet继承GenericServlet
public abstract class HttpServlet extends GenericServlet{
}
//GenericServlet实现Servlet
public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {
}
//servlet就是一个接口
public interface Servlet {
void init(ServletConfig var1) throws ServletException;
ServletConfig getServletConfig();
void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
String getServletInfo();
void destroy();
}
3.实现父类的方法
package com.saxon.servlet;
import javax.servlet.ServletException;
import javax.servlet.annotation.ServletSecurity;
import javax.servlet.annotation.WebServlet;
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 {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
PrintWriter writer = resp.getWriter ();
writer.print ("Hello, I am Saxon");
}
@Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet (req, resp);
}
}
4.编写servlet地址映射
<servlet>
<servlet-name>a</servlet-name>
<servlet-class>com.saxon.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon</url-pattern>
</servlet-mapping>
5.启动tomcat调试
二、原理:
在我们第一次使用浏览器加载项目时,项目会生成一个Target目录。当浏览器向客户端发出请求的时候,如果是第一次加载,那么就会去加载servlet,如果不是的话,就由web容器发出请求,请求具体访问我们的servlet的service方法。结束后在返还一个响应信息,web容器在返回一个响应给浏览器;(接收并处理要求和返回响应信息)
三、servlet mapping
servlet和servlet-mapping通过servlet-name,将servlet-class和url-pattern构成联系,从而使URL映射到类servlet-class所指定的类中
一、一个servlet对应一个servlet-mapping
<servlet>
<servlet-name>a</servlet-name>
<servlet-class>com.saxon.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon</url-pattern>
</servlet-mapping>
二、一个servlet对应多个servlet-mapping
<servlet>
<servlet-name>a</servlet-name>
<servlet-class>com.saxon.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon2</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon3</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon4</url-pattern>
</servlet-mapping>
三、一个servlet对应路径下所有的映射
<!-- 就是在路径下面加上一个*-->
<servlet>
<servlet-name>a</servlet-name>
<servlet-class>com.saxon.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/saxon/*</url-pattern>
</servlet-mapping>
四、修改默认请求的路径
默认访问的不是jsp了,而是我们绑定的servlet
<servlet>
<servlet-name>a</servlet-name>
<servlet-class>com.saxon.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
五、固定的文件后缀可以访问
*.saxon的前后不可以加任何的其他字,不然会报错;
<servlet>
<servlet-name>a</servlet-name>
<servlet-class>com.saxon.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>a</servlet-name>
<url-pattern>*.saxon</url-pattern>
</servlet-mapping>
Caused by: java.lang.IllegalArgumentException: servlet鏄犲皠涓殑<url pattern>[*.saxon/2]鏃犳晥 //乱码问题可以解决的,可以看出错误的原因就是<url pattern>中的问题
四、ServletContext
一、含义
servletContext接口是Servlet中最大的一个接口,呈现了web应用的Servlet视图。ServletContext实例是通过 getServletContext()方法获得的,由于HttpServlet继承GenericServlet的关系,GenericServlet类和HttpServlet类同时具有该方法。这是在servlet之上的一层结构,等级高一级 每个web应用都会有一个ServletContext对象与之关联
二、测试servlet之间的通信
1.上传
package com.saxon.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 send extends HttpServlet {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext ();
context.setAttribute ("saxon","saxon 是帅哥");
}
@Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet (req, resp);
}
}
2.接收
package com.saxon.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 get extends HttpServlet {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext ();
String saxon = (String)context.getAttribute ("saxon");
resp.setCharacterEncoding ("utf-8");//配置编码
resp.setContentType ("text/html");
resp.getWriter ().print (saxon);
}
@Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet (req, resp);
}
}
3.配置文件
<servlet>
<servlet-name>get</servlet-name>
<servlet-class>com.saxon.servlet.get</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>get</servlet-name>
<url-pattern>/get</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>send</servlet-name>
<servlet-class>com.saxon.servlet.send</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>send</servlet-name>
<url-pattern>/send</url-pattern>
</servlet-mapping>
要先放入在接收,才会显示结果
三、获得初始化参数
package com.saxon.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class GP extends HttpServlet {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext ();
String saxon = context.getInitParameter ("saxon");
resp.getWriter ().print (saxon);
}
@Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet (req, resp);
}
}
<context-param><!-- 这个就是我们的初始化文件-->
<param-name>saxon</param-name>
<param-value>jdbc:mysql://saxon:3306/test</param-value>
</context-param>
<servlet>
<servlet-name>gp</servlet-name>
<servlet-class>com.saxon.servlet.GP</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>gp</servlet-name>
<url-pattern>/gp</url-pattern>
</servlet-mapping>
四、请求转发
含义:就是在当前页面下跳转到另一个页面。servlet之间的跳转,但是地址(url)还是一样的;
package com.saxon.servlet;
import javax.servlet.RequestDispatcher;
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 Skip extends HttpServlet {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext ();
RequestDispatcher r = context.getRequestDispatcher ("/gp");//写入要跳转的页面的url-pattern
r.forward (req,resp);// void forward(ServletRequest var1, ServletResponse var2) 一个请求,一个响应
}
@Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet (req, resp);
}
}
<servlet>
<servlet-name>skip</servlet-name>
<servlet-class>com.saxon.servlet.Skip</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>skip</servlet-name>
<url-pattern>/skip</url-pattern>
</servlet-mapping>
tips⚡️:我们虽然跳到了其他的页面但是地址栏还是当前的地址,不会变;这就是与重定向的区别。他的Status Code是200;
五、读取配置文件
1.写一个配置文件
username=saxon
pwd=123456
2.编写测试servlet
package com.saxon.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 Properties_Servlet extends HttpServlet {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println (this.getServletContext ().getContextPath ());//Saxon_Servlet_Son_02_war
System.out.println ("start***************************");
InputStream is = this.getServletContext ().getResourceAsStream ("/WEB-INF/classes/lover.properties");//注意路径
Properties prop = new Properties ();
prop.load (is);
String username = prop.getProperty ("username");
String pwd = prop.getProperty ("pwd");
resp.getWriter ().print (username + ":" + pwd);
}
@Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet (req, resp);
}
}
由于当前servletcontext是在/Saxon_Servlet_Son_02_war目录下,我们也知道war包就是一个打包的web程序。所以我们的路径前面加上的/表示当前路径。我们在resource下面写的包就会到WEB-INF/classes/包下,如果我们将配置文件写在了Java目录中,我们可以在当前项目的文件pom.xml中加入一段代码;
<build>
<resources>
<resource>
<directory>src/main/resources</directory><!--你要导出资源的文件夹-->
<includes>
<include>**/*.properties</include><!-- 导出资源的类型-->
<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>
3.将这一个servlet加入web.xml
<servlet>
<servlet-name>prop</servlet-name>
<servlet-class>com.saxon.servlet.Properties_Servlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>prop</servlet-name>
<url-pattern>/prop</url-pattern>
</servlet-mapping>
4.启动tomcat,测试;
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