第 295 章 Camel SCR （已弃用）

camel-scr 捆绑包没有包括在 Apache Camel 之前的版本 2.15.0 中，但工件本身可以从 2.12.0 开始用于任何 Camel 版本。

org.apache.camel/camel-scr 捆绑包提供基本类 AbstractCamelRunner，它管理您和帮助程序类 ScrHelper，用于在单元测试中使用 SCR 属性。Camel-scr 功能可用于定义在 SCR 捆绑包中运行 Camel 所需的所有功能和捆绑包。

AbstractCamelRunner 类将 CamelContext 的生命周期与 Service 组件的生命周期相关联，并使用 Camel 的 PropertiesComponent 来处理配置。从 java 类中使一个 Service 组件从 AbstractCamelRunner 进行扩展，并在类级别上添加以下 org.apache.felix.scr.annotations ：

添加所需的注解

@Component
@References({
    @Reference(name = "camelComponent",referenceInterface = ComponentResolver.class,
        cardinality = ReferenceCardinality.MANDATORY_MULTIPLE, policy = ReferencePolicy.DYNAMIC,
        policyOption = ReferencePolicyOption.GREEDY, bind = "gotCamelComponent", unbind = "lostCamelComponent")
})

然后实施 getRouteBuilders （） 方法，该方法返回您要运行的 Camel 路由：

实施 getRouteBuilders （）

    @Override
    protected List<RoutesBuilder> getRouteBuilders() {
        List<RoutesBuilder> routesBuilders = new ArrayList<>();
        routesBuilders.add(new YourRouteBuilderHere(registry));
        routesBuilders.add(new AnotherRouteBuilderHere(registry));
        return routesBuilders;
    }

最后提供默认配置：

注解中的默认配置

@Properties({
   @Property(name = "camelContextId", value = "my-test"),
   @Property(name = "active", value = "true"),
   @Property(name = "...", value = "..."),
   ...
})

这一切。并且如果您使用 camel-archetype-scr 来生成一个项目，则这已经需要注意。

以下是由 camel-archetype-scr 生成的完整的 Service 组件类示例：

CamelScrExample.java

// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT
package example;

import java.util.ArrayList;
import java.util.List;

import org.apache.camel.scr.AbstractCamelRunner;
import example.internal.CamelScrExampleRoute;
import org.apache.camel.RoutesBuilder;
import org.apache.camel.spi.ComponentResolver;
import org.apache.felix.scr.annotations.*;

@Component(label = CamelScrExample.COMPONENT_LABEL, description = CamelScrExample.COMPONENT_DESCRIPTION, immediate = true, metatype = true)
@Properties({
    @Property(name = "camelContextId", value = "camel-scr-example"),
    @Property(name = "camelRouteId", value = "foo/timer-log"),
    @Property(name = "active", value = "true"),
    @Property(name = "from", value = "timer:foo?period=5000"),
    @Property(name = "to", value = "log:foo?showHeaders=true"),
    @Property(name = "messageOk", value = "Success: {{from}} -> {{to}}"),
    @Property(name = "messageError", value = "Failure: {{from}} -> {{to}}"),
    @Property(name = "maximumRedeliveries", value = "0"),
    @Property(name = "redeliveryDelay", value = "5000"),
    @Property(name = "backOffMultiplier", value = "2"),
    @Property(name = "maximumRedeliveryDelay", value = "60000")
})
@References({
    @Reference(name = "camelComponent",referenceInterface = ComponentResolver.class,
        cardinality = ReferenceCardinality.MANDATORY_MULTIPLE, policy = ReferencePolicy.DYNAMIC,
        policyOption = ReferencePolicyOption.GREEDY, bind = "gotCamelComponent", unbind = "lostCamelComponent")
})
public class CamelScrExample extends AbstractCamelRunner {

    public static final String COMPONENT_LABEL = "example.CamelScrExample";
    public static final String COMPONENT_DESCRIPTION = "This is the description for camel-scr-example.";

    @Override
    protected List<RoutesBuilder> getRouteBuilders() {
        List<RoutesBuilder> routesBuilders = new ArrayList<>();
        routesBuilders.add(new CamelScrExampleRoute(registry));
        return routesBuilders;
    }
}

CamelContextId 和 active 属性控制 CamelContext 的名称（默认为 "camel-runner-default"）以及是否要启动它（默认为 "false"。除了这些之外，您还可以添加和使用您想要的相同属性。Camel 的 PropertiesComponent 处理递归属性，并在没有问题的情况下使用回退前缀。

AbstractCamelRunner 将为您的 RouteBuilders 提供这些属性，并提供 Camel 的 PropertiesComponents，它还会在名称匹配时将这些值注入到您的 Service 组件和 RouteBuilder 字段中。可以使用任何可见性级别声明字段，并且支持许多类型（字符串、int、布尔值、URL、…​）。

以下是由 camel-archetype-scr 生成的 RouteBuilder 类的示例：

CamelScrExampleRoute.java

// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT
package example.internal;

import org.apache.camel.LoggingLevel;
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.impl.SimpleRegistry;
import org.apache.commons.lang.Validate;

public class CamelScrExampleRoute extends RouteBuilder {

    SimpleRegistry registry;

    // Configured fields
    private String camelRouteId;
    private Integer maximumRedeliveries;
    private Long redeliveryDelay;
    private Double backOffMultiplier;
    private Long maximumRedeliveryDelay;

    public CamelScrExampleRoute(final SimpleRegistry registry) {
        this.registry = registry;
    }

    @Override
    public void configure() throws Exception {
        checkProperties();

        // Add a bean to Camel context registry
        registry.put("test", "bean");

        errorHandler(defaultErrorHandler()
            .retryAttemptedLogLevel(LoggingLevel.WARN)
            .maximumRedeliveries(maximumRedeliveries)
            .redeliveryDelay(redeliveryDelay)
            .backOffMultiplier(backOffMultiplier)
            .maximumRedeliveryDelay(maximumRedeliveryDelay));

        from("{{from}}")
            .startupOrder(2)
            .routeId(camelRouteId)
            .onCompletion()
                .to("direct:processCompletion")
            .end()
            .removeHeaders("CamelHttp*")
            .to("{{to}}");


        from("direct:processCompletion")
            .startupOrder(1)
            .routeId(camelRouteId + ".completion")
            .choice()
                .when(simple("${exception} == null"))
                    .log("{{messageOk}}")
                .otherwise()
                    .log(LoggingLevel.ERROR, "{{messageError}}")
            .end();
        }
    }

    public void checkProperties() {
        Validate.notNull(camelRouteId, "camelRouteId property is not set");
        Validate.notNull(maximumRedeliveries, "maximumRedeliveries property is not set");
        Validate.notNull(redeliveryDelay, "redeliveryDelay property is not set");
        Validate.notNull(backOffMultiplier, "backOffMultiplier property is not set");
        Validate.notNull(maximumRedeliveryDelay, "maximumRedeliveryDelay property is not set");
    }
}

让我们一起查看 CamelScrExampleRoute。

    // Configured fields
    private String camelRouteId;
    private Integer maximumRedeliveries;
    private Long redeliveryDelay;
    private Double backOffMultiplier;
    private Long maximumRedeliveryDelay;

这些字段的值通过匹配其名称来使用来自属性的值。

        // Add a bean to Camel context registry
        registry.put("test", "bean");

如果需要将一些 Bean 添加到 CamelContext 的 registry 中用于路由，您可以执行以下操作：

    public void checkProperties() {
        Validate.notNull(camelRouteId, "camelRouteId property is not set");
        Validate.notNull(maximumRedeliveries, "maximumRedeliveries property is not set");
        Validate.notNull(redeliveryDelay, "redeliveryDelay property is not set");
        Validate.notNull(backOffMultiplier, "backOffMultiplier property is not set");
        Validate.notNull(maximumRedeliveryDelay, "maximumRedeliveryDelay property is not set");
    }

最好检查是否设置了所需的参数，并在允许路由启动前具有有意义的值。

        from("{{from}}")
            .startupOrder(2)
            .routeId(camelRouteId)
            .onCompletion()
                .to("direct:processCompletion")
            .end()
            .removeHeaders("CamelHttp*")
            .to("{{to}}");


        from("direct:processCompletion")
            .startupOrder(1)
            .routeId(camelRouteId + ".completion")
            .choice()
                .when(simple("${exception} == null"))
                    .log("{{messageOk}}")
                .otherwise()
                    .log(LoggingLevel.ERROR, "{{messageError}}")
            .end();

请注意，路由中的一切都配置有属性。这基本上使您的 RouteBuilder 成为模板。SCR 允许您通过提供替代配置来创建更多路由实例。有关使用 Camel SCR 捆绑包作为模板 的更多信息。