自制Filter过滤器

导依赖

<dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp.jstl</groupId>
            <artifactId>jstl-api</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
    </dependencies>

编写 过滤器

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

public class CharacterEncodingFilter implements Filter {
    //初始化方法 当服务器启动时执行
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化...");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf8");
        servletResponse.setCharacterEncoding("utf8");
        servletResponse.setContentType("text/html;charset=utf8");
        System.out.println("CharacterEncodingFilter执行前");
        filterChain.doFilter(servletRequest,servletResponse);//让我们的请求继续走，如果不写，程序到这里就被拦截停止
        System.out.println("CharacterEncodingFilter执行后");
    }
    //销毁方法 当服务器关闭执行
    @Override
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁了");
    }
}

编写servlet类

public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        writer.write("我是潮汕奴仔");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

在web.xml中注册servlet

<!--    配置servlet-->
    <servlet>
        <servlet-name>MyServlet</servlet-name>
        <servlet-class>com.csnz.servlet.MyServlet</servlet-class>
    </servlet>
<!--    servlet对应的映射-->
    <servlet-mapping>
        <servlet-name>MyServlet</servlet-name>
        <url-pattern>/servlet/MyServlet</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>MyServlet</servlet-name>
        <url-pattern>/MyServlet</url-pattern>
    </servlet-mapping>
    <!--    配置过滤器-->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.csnz.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>

启动服务器

发现乱码

有配置过滤器的正常输出
没有过滤器的会乱码