JavaWeb的过滤器（Filter）的两种配置

Filter接口

要成为一个Filter需要实现Filter接口

Filter生命周期

容器启动就创建Filter实例，先执行无参构造器，然后执行init()方法，以后每次要过滤的请求会执行doFilter()方法，容器关闭时，执行destroy()方法

public interface Filter {
public void init(FilterConfig filterConfig) throws ServletException;
public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException;
public void destroy();
}

一、xml配置

1.web.xml

在web.xml中配置Filter，指定对应的Filter类，映射信息，指定过滤哪些请求，/hello.jsp，请求hello.jsp时，先执行过滤器，设置初始化参数，告诉服务器都拦截哪些方式到达的资源

：

1)精确匹配：/路径名/资源名，要拦截资源的详细信息，/hello.jsp

2)路径匹配：/路径名/*，/*拦截所有

3)后缀匹配：*.后缀，所有一给定后缀结尾的都拦截

：

1)forward：拦截转发过来的

2)include：拦截包含的（动态包含会被拦截）

栗：hello.jsp页面包含test.jsp页面

静态包含<%@include file=&＃8221;test.jsp&＃8221; %>；动态包含

3)request：（默认）拦截直接请求的

4)error：发生错误（全局配置的一个错误页面会被拦截，例如，发生错误404,500转到hello.jsp）


404
/hello.jsp


500
/hello.jsp



HelloFilter
com.example.filter.HelloFilter

user
root



HelloFilter
/hello.jsp
REQUEST
FORWARD


2.Filter类

当请求为/hello.jsp?pwd=123时通过过滤器，可以访问hello.jsp，否则，不能够范围/hello.jsp

chain.doFilter()方法，请求传递到下一层

public class HelloFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
String user = filterConfig.getInitParameter("user");
System.out.println(user);
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
String pwd = request.getParameter("pwd");
if (pwd != null && "123".equals(pwd)){
chain.doFilter(request, response);
}else {
response.getWriter().write("failed");
}
}
@Override
public void destroy() {
}
}

二、@WebFilter注解配置

name等同于，urlPatterns等同于，initParams 等同于

@WebFilter(filterName = "HelloFilter",
urlPatterns = "/hello.jsp",
initParams = {
@WebInitParam(name = "user", value = "root")
})

2.Servlet类

@WebFilter(filterName = "HelloFilter",
urlPatterns = "/hello.jsp",
dispatcherTypes = {
DispatcherType.FORWARD, DispatcherType.INCLUDE
},
initParams = {
@WebInitParam(name = "user", value = "root"),
})
public class HelloFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
String user = filterConfig.getInitParameter("user");
System.out.println(user);
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
String pwd = request.getParameter("pwd");
if (pwd != null && "123".equals(pwd)){
chain.doFilter(request, response);
}else {
response.getWriter().write("failed");
}
}
@Override
public void destroy() {
}
}