Servlet vs Filter [英] Servlet vs Filter

问题描述

Servlet 和过滤器有什么区别？你建议用什么来授权页面？

What is the difference between a Servlet and Filter? What do you recommend to use for authorization to pages?

推荐答案

使用过滤器当您想要根据特定条件过滤和/或修改请求时。如果要控制，预处理和/或后处理请求，请使用 Servlet 。

Use a Filter when you want to filter and/or modify requests based on specific conditions. Use a Servlet when you want to control, preprocess and/or postprocess requests.

Java EE教程提到了以下有关过滤器的内容：

The Java EE tutorial mentions the following about filters:

过滤器是一个可以转换请求或响应的标头和内容（或两者）的对象。过滤器与Web组件的不同之处在于过滤器通常不会自行创建响应。相反，过滤器提供可以附加到任何类型的Web资源的功能。因此，过滤器不应该对作为过滤器的Web资源有任何依赖性;通过这种方式，它可以由多种类型的Web资源组成。

A filter is an object that can transform the header and content (or both) of a request or response. Filters differ from web components in that filters usually do not themselves create a response. Instead, a filter provides functionality that can be "attached" to any kind of web resource. Consequently, a filter should not have any dependencies on a web resource for which it is acting as a filter; this way it can be composed with more than one type of web resource.

过滤器可以执行的主要任务如下：

The main tasks that a filter can perform are as follows:

• 查询请求并采取相应行动。


• 阻止请求和响应对进一步传递。


• 修改请求标头和数据。您可以通过提供请求的自定义版本来执行此操作。


• 修改响应标头和数据。您可以通过提供自定义版本的响应来实现此目的。


• 与外部资源交互。

• Query the request and act accordingly.
• Block the request-and-response pair from passing any further.
• Modify the request headers and data. You do this by providing a customized version of the request.
• Modify the response headers and data. You do this by providing a customized version of the response.
• Interact with external resources.

对于授权，过滤器是最合适的。以下是过滤器如何检查已登录用户请求的基本启动示例：

For authorization, a Filter is the best suited. Here's a basic kickoff example of how a filter checks requests for the logged-in user:

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
    if (((HttpServletRequest) request).getSession().getAttribute("user") == null) {
        // User is not logged in. Redirect to login page.
        ((HttpServletResponse) response).sendRedirect("login");
    } else {
        // User is logged in. Just continue with request.
        chain.doFilter(request, response);
    }
}

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