编写过滤器

导包

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
 
        </dependency>
 
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</version>
 
        </dependency>
        <!-- https://mvnrepository.com/artifact/javax.servlet.jsp.jstl/jstl-api -->
        <dependency>
            <groupId>javax.servlet.jsp.jstl</groupId>
            <artifactId>jstl-api</artifactId>
            <version>1.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/taglibs/standard -->
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
        <!--连接数据库-->
        <dependency>
            <groupId>com.github.spt-oss</groupId>
            <artifactId>mysql-connector-java-plus</artifactId>
            <version>0.1.0</version>
        </dependency>
	 </dependencies>

编写过滤器

1. 导包
   
   2.重写三个方法

• init（初始化，在服务器启动时过滤器就开始初始化）
• doFilter(主要写这个)

	servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        System.out.println("过滤之前");
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("过滤之后");

• destroy（销毁，在服务器关闭的时候过滤器就销毁）

3. 在xml中配置filter文件

<filter>
        <filter-name>filterDemo</filter-name>
        <filter-class>com.Google.FilterDemo01</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filterDemo</filter-name>
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>