JAVA_WEB之Servlet

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

1
2
3

<modules>
        <module>Saxon_Servlet_Son_01</module>
</modules>

建项目吗?父子局

1	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

一、一个对应一个

<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>

二、一个对应多个

<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>
      <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、一个对应所有的映射

<!-- 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>

1	Caused by: java.lang.IllegalArgumentException: servlet鏄犲皠涓殑<url pattern>[*.saxon/2]鏃犳晥

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>
        <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；

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:zap::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

1 2	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；