过滤器

Filter例子

Filter:过滤器，用来过滤网站的数据

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Filter开发步骤

1-导maven坐标

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</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>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>

2-编写过滤器（共三步）

• 1-Filter导包不能出错：javax.servlet
• 2-实现Filter接口，实现对应的方法即可

public class CharacterEncodingFilter implements Filter {
//Filter导包：javax.servlet
    //重写三个方法
    //初始化,web服务器启动时，就开始初始化，随时等待过滤对象的出现
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化");
    }

//    filterChain:链
/*
1.过滤中的所有代码，在固定特定请求的时候，都会执行
2.必须要让过滤器继续通行（可能不止一个过滤器）：固定写法：filterChain.doFilter(servletRequest,servletResponse)
*
* */
    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("CharacterEncodingFilter初始化执行前...");
        filterChain.doFilter(servletRequest,servletResponse);//让请求继续走下去，如果不写，程序到这里拦截停止
        System.out.println("CharacterEncodingFilter初始化执行后...");
    }

    public void destroy() {
        //web服务器关闭的时候，才会销毁
        System.out.println("CharacterEncodingFilter销毁");
    }
}

• 3-配置xml

    <filter>
        <filter-name>filter</filter-name>
        <filter-class>com.kuang.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter</filter-name>
<!--        只要是/servlet下面的任何请求，都会经过这个过滤器-->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>