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java过滤器如何过滤

2026-02-05 03:56:17Java

Java过滤器的基本实现

在Java中，过滤器（Filter）是Servlet规范的一部分，主要用于在请求到达Servlet之前或响应发送给客户端之前对请求和响应进行预处理。过滤器的常见应用场景包括身份验证、日志记录、数据压缩、字符编码转换等。

创建过滤器类

创建一个过滤器需要实现javax.servlet.Filter接口。以下是一个简单的过滤器示例：

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

@WebFilter("/*")
public class SimpleFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化代码
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // 预处理请求
        System.out.println("Before servlet processing");

        // 将请求传递给下一个过滤器或Servlet
        chain.doFilter(request, response);

        // 后处理响应
        System.out.println("After servlet processing");
    }

    @Override
    public void destroy() {
        // 清理代码
    }
}

配置过滤器

过滤器可以通过注解或web.xml文件进行配置：

注解方式：

@WebFilter(urlPatterns = {"/*"}, initParams = {
    @WebInitParam(name = "param1", value = "value1")
})

web.xml方式：

<filter>
    <filter-name>SimpleFilter</filter-name>
    <filter-class>com.example.SimpleFilter</filter-class>
    <init-param>
        <param-name>param1</param-name>
        <param-value>value1</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>SimpleFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

常见过滤操作

字符编码过滤：

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
    request.setCharacterEncoding("UTF-8");
    response.setCharacterEncoding("UTF-8");
    chain.doFilter(request, response);
}

身份验证过滤：

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletResponse httpResponse = (HttpServletResponse) response;

    if (httpRequest.getSession().getAttribute("user") == null) {
        httpResponse.sendRedirect(httpRequest.getContextPath() + "/login");
        return;
    }

    chain.doFilter(request, response);
}

日志记录过滤：

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
    long startTime = System.currentTimeMillis();
    chain.doFilter(request, response);
    long duration = System.currentTimeMillis() - startTime;
    System.out.println("Request processing time: " + duration + "ms");
}