简介

Spring Listener是用于指定对象发生事件或状态改变的监听器

常见4种监听方式

监听 Servlet上下文对象


public class Test implements Serializable {
    private static final long serialVersionUID = -5442854457404278567L;
    private String name;

    public Test(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

@Service
public class TestService {
    public Test getTestObject() {
        return new Test("全爷 "+ System.currentTimeMillis());
    }
}

/**
 * 监听器, 实现 ApplicationListener接口
 * */
@Component
public class TestServletContextListener implements ApplicationListener<ContextRefreshedEvent> {
    private ApplicationContext applicationContext;

    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        /** 获取上下文*/
        applicationContext = contextRefreshedEvent.getApplicationContext();
        /** 将数据载入到应用域中*/
        onRefresh();
    }

    public void onRefresh() {
        /** 获取指定服务*/
        final TestService testService = applicationContext.getBean(TestService.class);
        /** 通过指定方法获取业务数据*/
        final Test test = testService.getTestObject();
        /** 获取应用域对象*/
        final ServletContext application = applicationContext.getBean(ServletContext.class);
        /** 将数据存到应用域中*/
        application.setAttribute("testObject", test);
    }
}

@RestController
public class TestController {
    @GetMapping("/index")
    public Map<String, Object> index(HttpServletRequest request) {
        ServletContext application = request.getServletContext();
        /** 从应用域中获取对象*/
        final Test test = (Test) application.getAttribute("testObject");
        final Map<String, Object> result = new HashMap<>();
        result.put("name", test.getName());
        return result;
    }

    @Autowired
    TestServletContextListener testServletContextListener;
    @GetMapping("/refresh")
    public Map<String, Object> refresh(HttpServletRequest request) {
        ServletContext application = request.getServletContext();
        /** 在应用域中删除指定对象*/
        application.removeAttribute("testObject");
        /** 将数据载入到应用域中*/
        testServletContextListener.onRefresh();
        final Map<String, Object> result = new HashMap<>();
        result.put("refresh", true);
        return result;
    }
}

# 请求地址 http://127.0.0.1:8080/index
# 输出
{"name":"全爷 1587382849292"}

# 请求地址 http://127.0.0.1:8080/refresh
# 输出
{"refresh":true}

监听 HTTP请求 Servlet Request对象

监听, 用户请求信息


@Component
public class TestServletRequestListener implements ServletRequestListener {
    @Override
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        HttpServletRequest request = (HttpServletRequest) servletRequestEvent.getServletRequest();
        System.out.println("Request init sessionId: " + request.getRequestedSessionId() + ", URL: " + request.getRequestURL());
        request.setAttribute("name", "全爷");
    }

    @Override
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
        HttpServletRequest request = (HttpServletRequest) servletRequestEvent.getServletRequest();
        System.out.println("Request end name: " + request.getAttribute("name"));
    }
}

@RestController
public class TestController {
    @GetMapping("/index")
    public Map<String, Object> index(HttpServletRequest request) {
        final Map<String, Object> result = new HashMap<>();
        result.put("name", request.getAttribute("name"));
        return result;
    }
}

# 请求地址 http://127.0.0.1:8080/index
# 输出
{"name":"全爷"}
# Console
Request init sessionId: null, URL: http://127.0.0.1:8080/index
Request end name: 全爷
Request init sessionId: null, URL: http://127.0.0.1:8080/favicon.ico
Request end name: 全爷

监听 HTTP会话 Session对象

监听, 在线用户数


/**
 * 记录在线的用户数
 */
@Component
public class TestHttpSessionListener implements HttpSessionListener {
    @Override
    public synchronized void sessionCreated(HttpSessionEvent httpSessionEvent) {
        Long count = (Long) httpSessionEvent.getSession().getServletContext().getAttribute("count");
        if (count == null) {
            count = 1L;
        } else {
            ++count;
        }
        System.out.println("新用户上线了: " + count);
        httpSessionEvent.getSession().getServletContext().setAttribute("count", count);
    }

    @Override
    public synchronized void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        Long count = (Long) httpSessionEvent.getSession().getServletContext().getAttribute("count");
        System.out.println("用户下线了: " + --count);
        httpSessionEvent.getSession().getServletContext().setAttribute("count", count);
    }
}

@RestController
public class TestController {
    @GetMapping("/index")
    public Map<String, Object> index(HttpServletRequest request) {
        final Map<String, Object> result = new HashMap<>();
        result.put("count", request.getSession().getServletContext().getAttribute("count"));
        return result;
    }
}

# 请求地址 http://127.0.0.1:8080/index
# 输出
{"count":1}

注: 测试时环境中设置 Session过期时间设置小一些
server.servlet.session.timeout=10s

监听自定义对象事件监听


/**
 * 自定义事件
 */
public class CustomEvent extends ApplicationEvent {
    private static final long serialVersionUID = -3106941444235503333L;
    private Test test;

    public CustomEvent(Object source, Test test) {
        super(source);
        this.test = test;
    }

    public Test getTest() {
        return test;
    }

    public void setTest(Test test) {
        this.test = test;
    }
}

/**
 * 自定义监听器
 * 实现 ApplicationListener接口, 监听 CustomEvent事件
 * */
@Component
public class CustomEventListener implements ApplicationListener<CustomEvent> {
    @Override
    public void onApplicationEvent(CustomEvent customEvent) {
        /** 从自定义事件获取信息*/
        Test test = customEvent.getTest();
        /** 在此处, 处理相关业务*/
        System.out.println("name: " + test.getName());
    }
}

@Service
public class TestService {
    @Resource
    private ApplicationContext applicationContext;

    public Test triggerEvent() {
        Test test = new Test("全爷 "+ System.currentTimeMillis());
        /** 触发事件*/
        CustomEvent event = new CustomEvent(this, test);
        applicationContext.publishEvent(event);
        return test;
    }
}

@RestController
public class TestController {
    @Autowired
    private TestService testService;

    @GetMapping("/index")
    public Map<String, Object> index() {
        testService.triggerEvent();
        final Map<String, Object> result = new HashMap<>();
        result.put("event", true);
        return result;
    }
}

# 请求地址 http://127.0.0.1:8080/index
# 输出
{"event":true}
# Console
name: 全爷 1587447532296

如果您觉得有帮助，欢迎点赞哦 ~ 谢谢!!

Spring监听器

Spring boot Listener

简介

常见4种监听方式

猜你喜欢