使用dwr（Direct Web Remoting）实现web前端的上线通知

“人怜花似旧，花不知人瘦”

序

现在做的智能眼镜项目，在眼镜端上线时，需要在web页面做通知。
效果如下：

实现

这里我就不多说dwr是什么了，可以参考百科或者官网。

1. 在pom.xml文件引入dwr和logging的依赖

            org.directwebremoting
            dwr
            3.0.2-RELEASE
        
        
            commons-logging
            commons-logging
            1.2
        

2. 创建dwr的配置文件dwr-spring-config.xml

3. 在项目启动时引入该配置文件，例如我这里是springboot项目，则在启动文件上添加引入文件的注释：

@EnableAutoConfiguration(exclude = {
        org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration.class
})
@EnableTransactionManagement
@ServletComponentScan
@MapperScan("com.xxx.*.dao")
@SpringBootApplication
@EnableCaching
@EnableSwagger2
//用于加载dwr配置上线通知的注解（这里需要注意：下面的文件上一定要加classpath，否则，在用maven--package打包时会报Caused by: java.io.FileNotFoundException: Could not open ServletContext resource [/dwr-spring-config.xml]的错）
@ImportResource(locations = "classpath:dwr-spring-config.xml")
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
        System.out.println("ヾ(◍°∇°◍)ﾉﾞ    启动成功      ヾ(◍°∇°◍)ﾉﾞ\n" +
                " ______                    _   ______            \n" +
                "|_   _ \\                  / |_|_   _ `.          \n" +
                "  | |_) |   .--.    .--. `| |-' | | `. \\  .--.   \n" +
                "  |  __'. / .'`\\ \\/ .'`\\ \\| |   | |  | |/ .'`\\ \\ \n" +
                " _| |__) || \\__. || \\__. || |, _| |_.' /| \\__. | \n" +
                "|_______/  '.__.'  '.__.' \\__/|______.'  '.__.'  ");
    }

    /**
     * dwr消息推送的配置
     * @return
     */
    @Bean
    public ServletRegistrationBean servletRegistrationBean() {
        DwrSpringServlet servlet = new DwrSpringServlet();
        ServletRegistrationBean registrationBean = new ServletRegistrationBean(servlet, "/dwr/*");
        Map initParameters = new HashMap();
        initParameters.put("debug", "true");
        initParameters.put("activeReverseAjaxEnabled","true");
        /*initParameters.put("pollAndCometEnabled","true");
        initParameters.put("crossDomainSessionSecurity","false");
        initParameters.put("allowScriptTagRemoting","true");*/
        registrationBean.setInitParameters(initParameters);
        return registrationBean;
    }
}

4. 创建MessagePush类，与页面建立连接

import org.directwebremoting.ScriptSession;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.annotations.RemoteMethod;
import org.directwebremoting.annotations.RemoteProxy;

import javax.servlet.ServletException;

@RemoteProxy(name = "MessagePush")
public class MessagePush {
    @RemoteMethod
    public void onPageLoad(String userId) {

        ScriptSession scriptSession = WebContextFactory.get().getScriptSession();
        scriptSession.setAttribute("userId", userId);
        System.out.println("测试dwr通知功能：" + userId);
        DwrScriptSessionManagerUtil dwrScriptSessionManagerUtil = new DwrScriptSessionManagerUtil();
        try {
            dwrScriptSessionManagerUtil.init();
        } catch (ServletException e) {
            e.printStackTrace();
        }
    }
}

5. 创建MessagePush需要依赖的类：

import org.directwebremoting.*;
import org.directwebremoting.event.ScriptSessionEvent;
import org.directwebremoting.event.ScriptSessionListener;
import org.directwebremoting.extend.ScriptSessionManager;
import org.directwebremoting.servlet.DwrServlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpSession;


public class DwrScriptSessionManagerUtil extends DwrServlet {
    public void init() throws ServletException {

        Container container = ServerContextFactory.get().getContainer();

        ScriptSessionManager manager = container .getBean(ScriptSessionManager.class);

        ScriptSessionListener listener = new ScriptSessionListener() {

            public void sessionCreated(ScriptSessionEvent ev) {

                HttpSession session = WebContextFactory.get().getSession();

                String userId = (String) session.getAttribute("userId");

                System.out.println("a ScriptSession is created!");

                ev.getSession().setAttribute("userId", userId);

            }

            public void sessionDestroyed(ScriptSessionEvent ev) {

                System.out.println("a ScriptSession is distroyed");

            }

        };
        manager.addScriptSessionListener(listener);

    }
}

6. 创建与页面交互的类：

import org.directwebremoting.Browser;
import org.directwebremoting.ScriptBuffer;
import org.directwebremoting.ScriptSession;

import javax.servlet.ServletException;
import java.util.Collection;
import java.util.List;

public class DwrUtil {

    /**
     * 调用页面javascript函数
     * @param functionName
     * @param args
     */
    public void invokeJavascriptFunction (String _funcName, List _args){
        final String funcName = _funcName;
        final List args = _args;
        DwrScriptSessionManagerUtil dwrScriptSessionManagerUtil = new DwrScriptSessionManagerUtil();
        try {
            dwrScriptSessionManagerUtil.init();
        } catch (ServletException e) {
            e.printStackTrace();
        }
       //全局通知
        Browser.withAllSessions(new Runnable(){
            private ScriptBuffer script = new ScriptBuffer();
            public void run(){
                //拼接javascript
                script = script.appendScript(funcName+"(");
                for(int i=0; i sessions = Browser.getTargetSessions();
                for (ScriptSession scriptSession : sessions){
                    scriptSession.addScript(script);
                }
            }
        });
    }
}

7. 在页面添加js引用，只需添加下面的引用即可，没有物理文件无妨：

8. 在页面加载时与java程序建立连接：

9. 在js中建方法，用于在java代码中调用

10. java代码中调用上面JavaScript的onlineReminder方法：

//推送到web端，通知上线
 DwrUtil t = new DwrUtil();
   List args = new ArrayList();
   args.add(mobile);
   args.add(appType);
   t.invokeJavascriptFunction("onlineReminder",args);