定义：在对项目中的资源发起请求时，可以通过配置的过滤规则，对指定的资源请求进行拦截，执行完过滤器中的逻辑之后，再根据
写法：①实现Filter接口，②实现init，doFilter，destroy方法，③在web.xml中配置过滤器
//配置文档方式↓
<filter>
<filter-name>Filter</filter-name>
<filter-class>com.Filter</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter</filter-name>
<url-pattern>/*</url-pattern>//可以指定过滤不同页面，此处是过滤所有页面
</filter-mapping>
//注解方式↓
@WebFilter(
filterName = "Filter",
urlPatterns = {"/*"},
initParams = {
@WebInitParam(name = "encoding",value = "UTF-8")
}
)
//判断当前页面有没有登录
<filter>
<filter-name>loginFilter</filter-name>
<filter-class>homework.filter.LoginFilter</filter-class>
<init-param>
<param-name>pass</param-name>
<param-value>login.jsp,register.jsp</param-value>//指定放行的页面
</init-param>
</filter>
<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>*.jsp</url-pattern>//过滤所有jsp页面
</filter-mapping>
//======================在LoginFilter.java取得需要放行的页面
public class LoginFilter implements Filter {
String[] pages=null;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("init LoginFilter");
pages=filterConfig.getInitParameter("pass").split(",");
for (String str:pages) {
System.out.println("who can pass-->"+str);
}
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("doFilter LoginFilter");
HttpServletRequest request = (HttpServletRequest)servletRequest;
HttpServletResponse response = (HttpServletResponse)servletResponse;
//1、取得客户端请求的资源名称
String uri = request.getRequestURI();
uri = uri.substring(uri.lastIndexOf("/")+1);
//2、判断请求的资源是否在放行之列，检查session中有没有用户信息
boolean isPass = false;
for(String page:pages){
if(page.equals(uri)){
isPass=true;
break;
}
}
if(isPass){
filterChain.doFilter(request,response);
}else {
Object object = request.getSession().getAttribute("no");
//3、有则放行，否则拦截
if(object !=null){
filterChain.doFilter(request,response);
}else{
request.setAttribute("message","请登录再试");
request.getRequestDispatcher("../homework/login.jsp").forward(request,response);
}
}
}
@Override
public void destroy() {
System.out.println("destroy LoginFilter");
}
}
//编码过滤
public class Filter_All implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("过滤器初始化");
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("过滤器执行");
HttpServletRequest request = (HttpServletRequest)servletRequest;
request.setCharacterEncoding("utf-8");
servletResponse.setCharacterEncoding("utf-8");
servletResponse.setContentType("text/html;charset=utf-8");
filterChain.doFilter(servletRequest,servletResponse);
}
@Override
public void destroy() {
System.out.println("过滤器被销毁");
}
}