在開發登錄模塊時，我們會使用攔截器進行是否已登錄的校驗等，通常會通過如下自定義一個攔截器

package com.demo.interceptors;import com.demo.service.ITestService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.servlet.HandlerInterceptor; import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public class TestInterceptor implements HandlerInterceptor {@Autowiredprivate ITestService testService;@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {this.testService.test();return false;}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {} }

并將該攔截器注冊到spring中

package com.demo.configure;import com.demo.interceptors.TestInterceptor; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configuration public class WebAppConfigure implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new TestInterceptor()).addPathPatterns("/**").excludePathPatterns("/login", "*.css", "*.js");} }

在攔截器中我們通常會調用Service中的方法，執行一些業務邏輯的判斷

package com.demo.service;public interface ITestService {void test();} package com.demo.service.impl;import com.demo.service.ITestService; import org.springframework.stereotype.Service;@Service public class TestService implements ITestService {@Overridepublic void test() {System.out.println("test");} }

當程序運行，并訪問時會出現空指針異常，如下圖所示

此時會發現TestInterceptor類中的testService為null，并沒有因為添加了@Autowird注解而注入進來。是因為在WebAppConfigure類中，是new出來的TestInterceptor對象，因此不會觸發spring的自動注入，導致空指針異常。

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可以通過如下兩種方式解決

1）將TestInterceptor類添加@Component注解，然后在WebAppConfigure類中使用@Autowird，將TestInterceptor對象注入進來

package com.demo.configure;import com.demo.interceptors.TestInterceptor; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configuration public class WebAppConfigure implements WebMvcConfigurer {@Autowiredprivate TestInterceptor testInterceptor;@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(testInterceptor).addPathPatterns("/**").excludePathPatterns("/login", "*.css", "*.js");} } package com.demo.interceptors;import com.demo.service.ITestService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import org.springframework.web.servlet.HandlerInterceptor; import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;@Component public class TestInterceptor implements HandlerInterceptor {@Autowiredprivate ITestService testService;@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {this.testService.test();return false;}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {} }

2）無需在TestInterceptor類上添加@Component直接，直接在WebAppConfigure類中添加經由@Bean注解的返回TestInterceptor對象的方法。

package com.demo.configure;import com.demo.interceptors.TestInterceptor; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configuration public class WebAppConfigure implements WebMvcConfigurer {@Beanpublic TestInterceptor testInterceptor() {return new TestInterceptor();}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(testInterceptor()).addPathPatterns("/**").excludePathPatterns("/login", "*.css", "*.js");} }

兩種方式都能夠使得TestInterceptor類中的testService不再為null，并且成功調用testService對象的test()方法

總結

以上是生活随笔為你收集整理的Spring中的Interceptor拦截器中使用@Autowired注解，在运行时会出现空指针的全部內容，希望文章能夠幫你解決所遇到的問題。

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