Filter过滤器

1.导包

点击查看代码

<dependencies>
        <!--Servlet 依赖-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>

        <!--JSP 依赖-->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <!--jstl表达式依赖 -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <!--standard标签库-->
        <!-- https://mvnrepository.com/artifact/taglibs/standard -->
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
    </dependencies>

**2.编写过滤器（Filter）** (注意 实现类的时候一定要选择javax.servlet)

点击查看代码

import javax.servlet.*;
import java.io.IOException;

public class CharacterFileter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("filter 开始初始化");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=utf-8");
        System.out.println("被执行前");
         filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("被执行后");
    }

    @Override
    public void destroy() {
        System.out.println("filter已经被销毁");
    }
}

3.在web.xml中注册Filter

点击查看代码

    <filter>
        <filter-name>filter</filter-name>
        <filter-class>com.xixi.filter.CharacterFileter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter</filter-name>
        <url-pattern>/Servlet/*</url-pattern>
    </filter-mapping>