Serving Web Content with Spring MVC

Spring MVC 框架是MVC设计模式的一种实现，因其简单易用、与Spring无缝融合等特性，被广泛应用在网站开发领域。

搭建第一个Spring MVC应用

实验目标

1.构建一个Web应用，当向浏览器地址 http://localhost:9001/greeting 发送GET请求时，返回

"Hello, World!"

2.给GET请求添加name参数，如 http://localhost:9001/greeting?name=User，返回对具体人名的问候语：

"Hello, User!"

Controller 层：注解方式

One of the successful implementation is Java Spring MVC. In Spring, if you want a class to be a controller you can use the annotation @RestController for this class. And in this class, use annotation @RequestMapping to show this is an RESTful API function.

HTTP报文如何解析到Controller方法？

Spring MVC框架的底层是Servlet。Servlet是一个标准，主要规定了处理请求与响应的service接口，在service接口中只需要实现业务逻辑即可。而Servlet由Servlet容器负责管理与运行，常见的Servlet容器有Tomcat，Jetty等。以Tomcat中的Servlet接口定义为例，如下所示：

由于Servlet只规定了接口，所以通常情况下不会直接继承Servlet进行实现，而是通过继承HttpServlet抽象类来有选择地覆盖相应的方法。而MVC更加方便，甚至不会去手动实现Servlet，只需要通过注解标注出Controller、Service、Model类即可，更加提高了开发的效率。

View 层实现：JSP

JSP是动态执行文件，由Tomcat生成java servlet执行文件。jsp中的内容被放到 _jspService() 方法体的 try...catch 代码块里执行。一个JSP文件的例子如下所示：

status.jsp

<li class="one"><a href="jsp/status.jsp">Home</a></li>

<div class="sectionTitle">Instance Info</div>
<table id='instanceInfo' class="stripeable">
    <tr><th>Name</th><th>Value</th></tr>
    <tr><td>ipAddr</td><td>192.168.1.104</td></tr><tr><td>status</td><td>UP</td></tr>
</table>
</div>

那么，当前 Eureka Server 的 InstanceInfo 是如何获取的呢？
status.jsp

146 StatusInfo statusInfo = (new StatusUtil(serverContext)).getStatusInfo();

StatusUtil.java

29 this.instanceInfo = server.getApplicationInfoManager().getInfo();

ApplicationInfoManager.java

58 private static ApplicationInfoManager instance = new ApplicationInfoManager(null, null, null);

@Inject
public ApplicationInfoManager(EurekaInstanceConfig config, InstanceInfo instanceInfo, OptionalArgs optionalArgs) {
    this.instanceInfo = instanceInfo;
    ......
}

调试后验证了，这里的instanceInfo一开始初始化是null，之后在BootStrap.java中才正式通过Builder初始化

@Deprecated
DiscoveryManager.java

/**
    * Initializes the <tt>Discovery Client</tt> with the given configuration.
    *
    * @param config
    *            the instance info configuration that will be used for
    *            registration with Eureka.
    * @param eurekaConfig the eureka client configuration of the instance.
    */
public void initComponent(EurekaInstanceConfig config,
                            EurekaClientConfig eurekaConfig, AbstractDiscoveryClientOptionalArgs args) {
    this.eurekaInstanceConfig = config;
    this.eurekaClientConfig = eurekaConfig;
    if (ApplicationInfoManager.getInstance().getInfo() == null) {
        // Initialize application info
        ApplicationInfoManager.getInstance().initComponent(config);
    }
    InstanceInfo info = ApplicationInfoManager.getInstance().getInfo();
    ......
}

ApplicationInfoManager.java

public void initComponent(EurekaInstanceConfig config) {
    try {
        this.config = config;
        this.instanceInfo = new EurekaConfigBasedInstanceInfoProvider(config).get();
    } catch (Throwable e) {
        throw new RuntimeException("Failed to initialize ApplicationInfoManager", e);
    }
}

EurekaBootStrap.java

161 EurekaInstanceConfig instanceConfig = isCloud(ConfigurationManager.getDeploymentContext())
                    ? new CloudInstanceConfig()
                    : new MyDataCenterInstanceConfig(); // 调试发现用的是 MyDataCenterInstanceConfig()
165         applicationInfoManager = new ApplicationInfoManager(
                instanceConfig, new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get());

EurekaConfigBasedInstanceInfoProvider.java

builder.setNamespace(config.getNamespace())
        .setInstanceId(instanceId)
        .setAppName(config.getAppname())
        .setAppGroupName(config.getAppGroupName())
        .setDataCenterInfo(config.getDataCenterInfo())
        .setIPAddr(config.getIpAddress())
        .setHostName(defaultAddress)
        .setPort(config.getNonSecurePort())
        .enablePort(PortType.UNSECURE, config.isNonSecurePortEnabled())
        .setSecurePort(config.getSecurePort())
        .enablePort(PortType.SECURE, config.getSecurePortEnabled())
        .setVIPAddress(config.getVirtualHostName())
        .setSecureVIPAddress(config.getSecureVirtualHostName())
        .setHomePageUrl(config.getHomePageUrlPath(), config.getHomePageUrl())
        .setStatusPageUrl(config.getStatusPageUrlPath(), config.getStatusPageUrl())
        .setASGName(config.getASGName())
        .setHealthCheckUrls(config.getHealthCheckUrlPath(),
                config.getHealthCheckUrl(), config.getSecureHealthCheckUrl());

于是我们在builder. 后面加入 .setAccountAddress(accountAddress)

在 InstanceInfo.java 中的 Builder 类中添加

public Builder setAccountAddress(String accountAddress) {
    result.accountAddress = accountAddress;
    return this;
}

继续调试发现 EurekaBootStrap.java 这段代码速度很慢

214 // Copy registry from neighboring eureka node
215 int registryCount = registry.syncUp();