拦截器是 Web 项目很重要和常用的功能，如对用户权限验证，判断用户是否已登录等。
SpringMVC 中的拦截器通过实现HanderInterceptor接口来完成，或继承抽象类HandlerInterceptorAdapter，重写里面的方法来完成。
HanderInterceptor
HanderInterceptor 接口中定义了三个方法，SpringMVC 通过这三个方法来对用户请求进行拦截处理。
boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
本方法在请求处理之前执行，返回值是 Boolean 类型，返回值为 false 时，表示请求结束；返回 true 时就会继承调用下一个 interceptor 的 preHandle() 方法，如果是最后一个 Interceptor，就调用当前请求的 Controller 方法。SpringMVC 中的 Interceptor 是链式调用，即在一个应用中或一个请求中可以同时存在多个Interceptor, 调用的的顺序是根据声明的顺序依次执行；所以可以在该方法中对一些请求做一个预处理，或初始化操作。
handler 参数是目标处理方法，是 HandlerMethod 类型，即处理请求的具体方法。可以通过该参数获取目标方法对象，再根据目标方法对象获取方法上的注解，再根据注解进行业务处理。
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| HandlerMethod handler1 = (HandlerMethod) handler;
Method method1 = handler1.getMethod();
RequestMapping methodAnnotation = handler1.getMethodAnnotation(RequestMapping.class);
if (null != methodAnnotation) {
System.out.println("-----------------");
}
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void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
preHandle()方法返回true;,请求被处理之后，也就是 Controller 方法被调用之后执行，但是在DispatcherServlet 进行视图返回渲染之前被调用。
多个 Interceptor 时，该方法的调用顺序与 preHandle() 相反。
void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
preHandle() 方法返回true,整个请求结束之后，DispatcherServlet 进行视图返回渲染之后执行。该方法主要作用是进行资源清理。
接口源码
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| public interface HandlerInterceptor {
default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return true;
}
default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
@Nullable ModelAndView modelAndView) throws Exception {
}
default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
@Nullable Exception ex) throws Exception {
}
}
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拦截器链调用顺序
实现示例
登录认证拦截器
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| import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import com.anqi.entity.User;
public class LoginInterceptor implements HandlerInterceptor {
private static final String[] IGNORE_URI = { "/loginForm", "/login", "/register" };
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object obj) throws Exception {
boolean flag = false;
String servletPath = request.getServletPath();
for (String uri : IGNORE_URI) {
if (servletPath.contains(uri)) {
flag = true;
break;
}
}
if (!flag) {
HttpSession session = request.getSession();
User user = (User) session.getAttribute("user");
if (user == null || "".equals(user.toString())) {
request.setAttribute("msg", "请先登录");
request.getRequestDispatcher("loginForm").forward(request, response);
return false;
} else {
flag = true;
}
}
return flag;
}
@Override
public void postHandle(HttpServletRequest req, HttpServletResponse resp, Object obj, ModelAndView exception)
throws Exception {
}
@Override
public void afterCompletion(HttpServletRequest req, HttpServletResponse resp, Object obj, Exception exception)
throws Exception {
}
}
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登录Token认证拦截器
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| public class AuthenticationInterceptor implements HandlerInterceptor {
@Autowired
UserService userService;
@Override
public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object object) throws Exception {
String token = httpServletRequest.getHeader("token");
if(!(object instanceof HandlerMethod)){
return true;
}
HandlerMethod handlerMethod=(HandlerMethod)object;
Method method=handlerMethod.getMethod();
if (method.isAnnotationPresent(PassToken.class)) {
PassToken passToken = method.getAnnotation(PassToken.class);
if (passToken.required()) {
return true;
}
}
if (method.isAnnotationPresent(UserLoginToken.class)) {
UserLoginToken userLoginToken = method.getAnnotation(UserLoginToken.class);
if (userLoginToken.required()) {
if (token == null) {
throw new RuntimeException("无token，请重新登录");
}
String userId;
try {
userId = JWT.decode(token).getAudience().get(0);
} catch (JWTDecodeException j) {
throw new RuntimeException("401");
}
User user = userService.findUserById(userId);
if (user == null) {
throw new RuntimeException("用户不存在，请重新登录");
}
JWTVerifier jwtVerifier = JWT.require(Algorithm.HMAC256(user.getPassword())).build();
try {
jwtVerifier.verify(token);
} catch (JWTVerificationException e) {
throw new RuntimeException("401");
}
return true;
}
}
return true;
}
@Override
public void postHandle(HttpServletRequest httpServletRequest,
HttpServletResponse httpServletResponse,
Object o, ModelAndView modelAndView) throws Exception {
}
@Override
public void afterCompletion(HttpServletRequest httpServletRequest,
HttpServletResponse httpServletResponse,
Object o, Exception e) throws Exception {
}
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装配拦截器
拦截/admin/开头的所有请求。
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<mvc:interceptors>
<mvc:interceptor>
<mvc:mapping path="/admin/**" />
<bean class="com.interceptor.LoginInterceptor"></bean>
</mvc:interceptor>
</mvc:interceptors>
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