Apache Camel –从头开始开发应用程序（第2部分/第2部分）

这是本教程的第二部分，我们将使用Apache Camel创建发票处理应用程序。如果您错过了它，一定要看一下第一部分。以前，我们已经定义了系统的功能要求，创建了网关，分离器，过滤器和基于内容的路由器组件。让我们继续创建一个转换器。

5.将发票转换为付款

现在，我们已经成功地从系统中过滤掉了“过于昂贵”的发票（它们可能需要人工检查等）。重要的是，我们现在可以收取发票并从中产生付款。首先，让我们将Payment类添加到banking包中：

package com.vrtoonjava.banking;import com.google.common.base.Objects;import java.math.BigDecimal;public class Payment {private final String senderAccount;private final String receiverAccount;private final BigDecimal dollars;public Payment(String senderAccount, String receiverAccount, BigDecimal dollars) {this.senderAccount = senderAccount;this.receiverAccount = receiverAccount;this.dollars = dollars;}public String getSenderAccount() {return senderAccount;}public String getReceiverAccount() {return receiverAccount;}public BigDecimal getDollars() {return dollars;}@Overridepublic String toString() {return Objects.toStringHelper(this).add("senderAccount", senderAccount).add("receiverAccount", receiverAccount).add("dollars", dollars).toString();}}

因为我们将有两种方法（从本地和国外发票）创建付款，所以我们定义一个用于创建付款的通用合同（界面）。将界面PaymentCreator放入banking包：

package com.vrtoonjava.banking;import com.vrtoonjava.invoices.Invoice;/*** Creates payment for bank from the invoice.* Real world implementation might do some I/O expensive stuff.*/
public interface PaymentCreator {Payment createPayment(Invoice invoice) throws PaymentException;}

从技术上讲，这是一个简单的参数化工厂。请注意，它将引发PaymentException 。稍后我们将进行异常处理，但这是简单的PaymentException的代码：

package com.vrtoonjava.banking;public class PaymentException extends Exception {public PaymentException(String message) {super(message);}}

现在，我们可以将两个实现添加到invoices包中了。首先，让我们创建LocalPaymentCreator类：

package com.vrtoonjava.invoices;import com.vrtoonjava.banking.Payment;
import com.vrtoonjava.banking.PaymentCreator;
import com.vrtoonjava.banking.PaymentException;
import org.springframework.stereotype.Component;@Component
public class LocalPaymentCreator implements PaymentCreator {// hard coded account value for demo purposesprivate static final String CURRENT_LOCAL_ACC = "current-local-acc";@Overridepublic Payment createPayment(Invoice invoice) throws PaymentException {if (null == invoice.getAccount()) {throw new PaymentException("Account can not be empty when creating local payment!");}return new Payment(CURRENT_LOCAL_ACC, invoice.getAccount(), invoice.getDollars());}}

另一个创建者将是ForeignPaymentCreator ，它具有相当简单的实现：

package com.vrtoonjava.invoices;import com.vrtoonjava.banking.Payment;
import com.vrtoonjava.banking.PaymentCreator;
import com.vrtoonjava.banking.PaymentException;
import org.springframework.stereotype.Component;@Component
public class ForeignPaymentCreator implements PaymentCreator {// hard coded account value for demo purposesprivate static final String CURRENT_IBAN_ACC = "current-iban-acc";@Overridepublic Payment createPayment(Invoice invoice) throws PaymentException {if (null == invoice.getIban()) {throw new PaymentException("IBAN mustn't be null when creating foreign payment!");}return new Payment(CURRENT_IBAN_ACC, invoice.getIban(), invoice.getDollars());}}

这两个创建者是简单的Spring bean，Apache Camel提供了一种将它们连接到路由的非常好的方法。我们将在Camel的Java DSL上使用transform()方法创建两个转换器。我们将正确的转换器插入seda:foreignInvoicesChannel seda:localInvoicesChannel和seda:foreignInvoicesChannel seda:localInvoicesChannel ，并使它们将结果转发到seda:bankingChannel 。将以下代码添加到您的configure方法中：

from("seda:foreignInvoicesChannel").transform().method("foreignPaymentCreator", "createPayment").to("seda:bankingChannel");from("seda:localInvoicesChannel").transform().method("localPaymentCreator", "createPayment").to("seda:bankingChannel");

6.将付款转到银行服务（服务激活器）

付款准备就绪，包含付款的消息正在seda:bankingChannel中等待。该流程的最后一步是使用Service Activator组件。它的工作方式很简单–当频道中出现新消息时，Apache Camel会调用Service Activator组件中指定的逻辑。换句话说，我们正在将外部服务连接到我们现有的消息传递基础结构。
为此，我们首先需要查看银行服务合同。因此，将BankingService接口BankingService到banking程序包中（在现实世界中，它可能驻留在某些外部模块中）：

package com.vrtoonjava.banking;/*** Contract for communication with bank.*/
public interface BankingService {void pay(Payment payment) throws PaymentException;}

现在，我们将需要BankingService的实际实现。同样，实现不太可能驻留在我们的项目中（它可能是远程公开的服务），但是至少出于教程目的，让我们创建一些模拟实现。将MockBankingService类添加到banking包：

package com.vrtoonjava.banking;import org.springframework.stereotype.Service;import java.util.Random;/*** Mock service that simulates some banking behavior.* In real world, we might use some web service or a proxy of real service.*/
@Service
public class MockBankingService implements BankingService {private final Random rand = new Random();@Overridepublic void pay(Payment payment) throws PaymentException {if (rand.nextDouble() > 0.9) {throw new PaymentException("Banking services are offline, try again later!");}System.out.println("Processing payment " + payment);}}

模拟实施会在某些随机情况下（约10％）造成失败。当然，为了实现更好的解耦，我们不会直接使用它，而是将根据自定义组件在合同（接口）上创建依赖关系。让我们现在将PaymentProcessor类添加到invoices包中：

package com.vrtoonjava.invoices;import com.vrtoonjava.banking.BankingService;
import com.vrtoonjava.banking.Payment;
import com.vrtoonjava.banking.PaymentException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;/*** Endpoint that picks Payments from the system and dispatches them to the* service provided by bank.*/
@Component
public class PaymentProcessor {@AutowiredBankingService bankingService;public void processPayment(Payment payment) throws PaymentException {bankingService.pay(payment);}}

Apache Camel提供了一种简单的方法，当消息到达特定端点时，如何在任意bean上调用方法（ EIP将其描述为服务激活器），方法是在Camel的Java DSL上使用bean()方法：

from("seda:bankingChannel").bean(PaymentProcessor.class, "processPayment");

错误处理

消息传递系统的最大挑战之一是正确识别和处理错误情况。 EAI描述了许多方法，我们将使用Camel的Dead Letter Channel EIP的实现。死信通道只是另一个通道，当该通道中出现错误消息时，我们可以采取适当的措施。在实际的应用程序中，我们可能会寻求一些重试逻辑或专业报告，在我们的示例教程中，我们只会打印出错误原因。让我们修改先前定义的Service Activator并插入errorHandler()组件。当PaymentProcessor引发异常时，此errorHandler会将引起错误的原始消息转发到Dead Letter Channel：

from("seda:bankingChannel").errorHandler(deadLetterChannel("log:failedPayments")).bean(PaymentProcessor.class, "processPayment");

最后，这是最终的完整路线：

package com.vrtoonjava.routes;import com.vrtoonjava.invoices.LowEnoughAmountPredicate;
import com.vrtoonjava.invoices.PaymentProcessor;
import org.apache.camel.LoggingLevel;
import org.apache.camel.builder.RouteBuilder;
import org.springframework.stereotype.Component;@Component
public class InvoicesRouteBuilder extends RouteBuilder {@Overridepublic void configure() throws Exception {from("seda:newInvoicesChannel").log(LoggingLevel.INFO, "Invoices processing STARTED").split(body()).to("seda:singleInvoicesChannel");from("seda:singleInvoicesChannel").filter(new LowEnoughAmountPredicate()).to("seda:filteredInvoicesChannel");from("seda:filteredInvoicesChannel").choice().when().simple("${body.isForeign}").to("seda:foreignInvoicesChannel").otherwise().to("seda:localInvoicesChannel");from("seda:foreignInvoicesChannel").transform().method("foreignPaymentCreator", "createPayment").to("seda:bankingChannel");from("seda:localInvoicesChannel").transform().method("localPaymentCreator", "createPayment").to("seda:bankingChannel");from("seda:bankingChannel").errorHandler(deadLetterChannel("log:failedPayments")).bean(PaymentProcessor.class, "processPayment");}}

运行整个事情

现在，我们将创建一个作业（它将以固定的速率）将新发票发送到系统。它只是利用Spring的@Scheduled注释的标准Spring bean。因此，我们向项目添加一个新类– InvoicesJob ：

package com.vrtoonjava.invoices;import org.apache.camel.Produce;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;import java.util.ArrayList;
import java.util.Collection;
import java.util.List;@Component
public class InvoicesJob {private int limit = 10; // default value, configurable@AutowiredInvoiceCollectorGateway invoiceCollector;@AutowiredInvoiceGenerator invoiceGenerator;@Scheduled(fixedRate = 4000)public void scheduleInvoicesHandling() {Collection<Invoice> invoices = generateInvoices(limit);System.out.println("\n===========> Sending " + invoices.size() + " invoices to the system");invoiceCollector.collectInvoices(invoices);}// configurable from Injectorpublic void setLimit(int limit) {this.limit = limit;}private Collection<Invoice> generateInvoices(int limit) {List<Invoice> invoices = new ArrayList<>();for (int i = 0; i < limit; i++) {invoices.add(invoiceGenerator.nextInvoice());}return invoices;}
}

Job会调用（每4秒一次） InvoicesGenerator并将发票转发到Gateway（我们了解的第一个组件）。为了使其工作，我们还需要InvoicesGenerator类：

package com.vrtoonjava.invoices;import org.springframework.stereotype.Component;import java.math.BigDecimal;
import java.util.Random;/*** Utility class for generating invoices.*/
@Component
public class InvoiceGenerator {private Random rand = new Random();public Invoice nextInvoice() {return new Invoice(rand.nextBoolean() ? iban() : null, address(), account(), dollars());}private BigDecimal dollars() {return new BigDecimal(1 + rand.nextInt(20_000));}private String account() {return "test-account " + rand.nextInt(1000) + 1000;}private String address() {return "Test Street " + rand.nextInt(100) + 1;}private String iban() {return "test-iban-" + rand.nextInt(1000) + 1000;}}

这只是一个简单的模拟功能，可让我们看到系统的运行情况。在现实世界中，我们不会使用任何生成器，而可能会使用某些公开的服务。

现在，在resources文件夹下创建一个新的spring配置文件– invoices-context.xml并声明组件扫描和任务计划支持：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns = "http://www.springframework.org/schema/beans"xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xmlns:task = "http://www.springframework.org/schema/task"xmlns:context = "http://www.springframework.org/schema/context"xsi:schemaLocation = "http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"><import resource = "camel-config.xml" /><context:component-scan base-package = "com.vrtoonjava" /><task:executor id = "executor" pool-size="10" /><task:scheduler id = "scheduler" pool-size="10" /><task:annotation-driven executor="executor" scheduler="scheduler" /></beans>

要查看整个运行过程，我们还需要最后一块-标准Java主应用程序，我们将在其中创建Spring的ApplicationContext。

package com.vrtoonjava.invoices;import org.springframework.context.support.ClassPathXmlApplicationContext;/*** Entry point of the application.* Creates Spring context, lets Spring to schedule job and use schema.*/
public class InvoicesApplication {public static void main(String[] args) {new ClassPathXmlApplicationContext("/invoices-context.xml");}}

只需从命令行运行mvn clean install并在InvoicesApplication类中启动main方法。您应该能够看到类似的输出：

===========> Sending 10 invoices to the system
13:48:54.347 INFO  [Camel (camel-1) thread #0 - seda://newInvoicesChannel][route1] Invoices processing STARTED
Amount of $4201 can be automatically processed by system
Amount of $15110 can not be automatically processed by system
Amount of $17165 can not be automatically processed by system
Amount of $1193 can be automatically processed by system
Amount of $6077 can be automatically processed by system
Amount of $17164 can not be automatically processed by system
Amount of $11272 can not be automatically processed by system
Processing payment Payment{senderAccount=current-local-acc, receiverAccount=test-account 1901000, dollars=4201}
Amount of $3598 can be automatically processed by system
Amount of $14449 can not be automatically processed by system
Processing payment Payment{senderAccount=current-local-acc, receiverAccount=test-account 8911000, dollars=1193}
Amount of $12486 can not be automatically processed by system
13:48:54.365 INFO  [Camel (camel-1) thread #5 - seda://bankingChannel][failedPayments] Exchange[ExchangePattern: InOnly, BodyType: com.vrtoonjava.banking.Payment, Body: Payment{senderAccount=current-iban-acc, receiverAccount=test-iban-7451000, dollars=6077}]
Processing payment Payment{senderAccount=current-iban-acc, receiverAccount=test-iban-6201000, dollars=3598}

参考： Apache Camel –在vrtoonjava博客上从JCG合作伙伴 Michal Vrtiak 从头开始开发应用程序（第2部分/第2部分）。