301.7. 示例

请参阅 Servlet Tomcat 示例。

当在 Camel/Spring 应用程序中使用 Servlet 组件时，通常需要在 Servlet 组件启动后加载 Spring ApplicationContext。这可以通过使用 Spring 的 ContextLoaderServlet 而不是 ContextLoaderListener 来完成。在这种情况下，您需要在 CamelHttpTransportServlet 后启动 ContextLoaderServlet，如下所示：

<web-app>
  <servlet>
        <servlet-name>CamelServlet</servlet-name>
        <servlet-class>
            org.apache.camel.component.servlet.CamelHttpTransportServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet>
        <servlet-name>SpringApplicationContext</servlet-name>
        <servlet-class>
            org.springframework.web.context.ContextLoaderServlet
        </servlet-class>
        <load-on-startup>2</load-on-startup>
  </servlet>
<web-app>

在 Camel 2.6.0 中，您可以使用类似如下的蓝图发布 CamelHttpTransportServlet 作为 OSGi 服务：

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <bean id="camelServlet" class="org.apache.camel.component.servlet.CamelHttpTransportServlet" />

    <!--
        Enlist it in OSGi service registry.
        This will cause two things:
        1) As the pax web whiteboard extender is running the CamelServlet will
           be registered with the OSGi HTTP Service
        2) It will trigger the HttpRegistry in other bundles so the servlet is
           made known there too
    -->
    <service ref="camelServlet">
        <interfaces>
            <value>javax.servlet.Servlet</value>
            <value>org.apache.camel.http.common.CamelServlet</value>
        </interfaces>
        <service-properties>
            <entry key="alias" value="/camel/services" />
            <entry key="matchOnUriPrefix" value="true" />
            <entry key="servlet-name" value="CamelServlet" />
        </service-properties>
    </service>

</blueprint>

然后，在您的 Camel 路由中使用这个服务，如下所示：

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:ext="http://aries.apache.org/blueprint/xmlns/blueprint-ext/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <reference id="servletref" ext:proxy-method="classes" interface="org.apache.camel.http.common.CamelServlet">
        <reference-listener ref="httpRegistry" bind-method="register" unbind-method="unregister" />
    </reference>

    <bean id="httpRegistry" class="org.apache.camel.component.servlet.DefaultHttpRegistry" />

    <bean id="servlet" class="org.apache.camel.component.servlet.ServletComponent">
        <property name="httpRegistry" ref="httpRegistry" />
    </bean>

    <bean id="servletProcessor" class="org.apache.camel.example.servlet.ServletProcessor" />

    <camelContext xmlns="http://camel.apache.org/schema/blueprint">
        <route>
            <!-- Notice how we can use the servlet scheme which is that reference above -->
            <from uri="servlet://hello" />
            <process ref="servletProcessor" />
        </route>
    </camelContext>

</blueprint>

对于 Camel 2.6 之前的版本，您可以使用 Activator 在 OSGi 平台上发布 CamelHttpTransportServlet ：

import java.util.Dictionary;
import java.util.Hashtable;

import org.apache.camel.component.servlet.CamelHttpTransportServlet;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.http.HttpContext;
import org.osgi.service.http.HttpService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.osgi.context.BundleContextAware;

public final class ServletActivator implements BundleActivator, BundleContextAware {
    private static final Logger LOG = LoggerFactory.getLogger(ServletActivator.class);
    private static boolean registerService;

    /**
     * HttpService reference.
     */
    private ServiceReference<?> httpServiceRef;

    /**
     * Called when the OSGi framework starts our bundle
     */
    public void start(BundleContext bc) throws Exception {
        registerServlet(bc);
    }

    /**
     * Called when the OSGi framework stops our bundle
     */
    public void stop(BundleContext bc) throws Exception {
        if (httpServiceRef != null) {
            bc.ungetService(httpServiceRef);
            httpServiceRef = null;
        }
    }

    protected void registerServlet(BundleContext bundleContext) throws Exception {
        httpServiceRef = bundleContext.getServiceReference(HttpService.class.getName());

        if (httpServiceRef != null && !registerService) {
            LOG.info("Register the servlet service");
            final HttpService httpService = (HttpService)bundleContext.getService(httpServiceRef);
            if (httpService != null) {
                // create a default context to share between registrations
                final HttpContext httpContext = httpService.createDefaultHttpContext();
                // register the hello world servlet
                final Dictionary<String, String> initParams = new Hashtable<String, String>();
                initParams.put("matchOnUriPrefix", "false");
                initParams.put("servlet-name", "CamelServlet");
                httpService.registerServlet("/camel/services", // alias
                    new CamelHttpTransportServlet(), // register servlet
                    initParams, // init params
                    httpContext // http context
                );
                registerService = true;
            }
        }
    }

    public void setBundleContext(BundleContext bc) {
        try {
            registerServlet(bc);
        } catch (Exception e) {
            LOG.error("Cannot register the servlet, the reason is " + e);
        }
    }

}

从 Camel 2.19.0 开始，camel-servlet-starter 库会在 /camel PROFILE 上下文路径下自动绑定所有剩余的端点。下表总结了 camel-servlet-starter 库中提供的其他配置属性。也可以禁用 Camel servlet 的自动映射。