在filter中使用dispatcher的步骤如下:
1. 在filter中引入dispatcher类,例如:
```java
import javax.servlet.DispatcherType;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
```
2. 在filter类上使用`@WebFilter`注解,并设置dispatcherTypes属性为需要拦截的dispatcher类型,例如:
```java
@WebFilter(urlPatterns = "/*", dispatcherTypes = {DispatcherType.REQUEST, DispatcherType.FORWARD})
public class MyFilter implements Filter {
// ...
}
```
上述示例中,设置了拦截所有URL,并只拦截REQUEST和FORWARD类型的dispatcher。
3. 在filter的`doFilter`方法中,通过`getRequestDispatcher`方法获取dispatcher对象,例如:
```java
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest httpRequest = (HttpServletRequest) request;
HttpServletResponse httpResponse = (HttpServletResponse) response;
RequestDispatcher dispatcher = httpRequest.getRequestDispatcher("/some-path");
// 使用dispatcher对象进行请求转发或包含
dispatcher.forward(httpRequest, httpResponse);
// 继续调用filter链中的下一个filter
chain.doFilter(request, response);
}
```
上述示例中,使用`getRequestDispatcher`方法获取了一个dispatcher对象,并通过它进行了请求转发`forward`。
注意:在filter中使用dispatcher时,需要确保在`chain.doFilter(request, response);`之前使用dispatcher对象进行请求转发或包含操作,以确保请求能够被正确处理。