Spring集成–从头开始应用程序，第2部分

这是本教程的第二部分，我们将使用Spring Integration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类添加到银行
包：

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放入银行业务包：

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发票包中了。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.integration.annotation.Transformer;
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';@Override@Transformerpublic 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.integration.annotation.Transformer;
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';@Override@Transformerpublic 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());}}

有关创建者的有趣部分是@Transformer批注。这是与@Filter注释一起使用的概念类似–只是这次我们告诉Spring Integration它应该使用此方法进行有效负载转换逻辑。无论哪种方式，我们都将使用外部或本地转换器，因此新消息将在BankingChannel通道中结束。让我们在架构文件中定义这些新的转换器：

<int:transformerinput-channel='localTransactions'output-channel='bankingChannel'ref='localPaymentCreator' /><int:transformerinput-channel='foreignTransactions'output-channel='bankingChannel'ref='foreignPaymentCreator' /><int:channel id = 'bankingChannel'><int:queue capacity='1000' />
</int:channel>

6.将付款转到银行服务（服务激活器）

付款已准备就绪，包含付款的消息正在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-当新消息出现在通道中时，Spring Integration会调用Service Activator组件中指定的逻辑。因此，当新的付款出现在bankingChannel中时，我们希望将其传递给银行服务。
为此，我们首先需要查看银行服务合同。因此，将BankingService接口添加到银行程序包中（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类添加到银行业务包：

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类添加到发票包中：

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.integration.annotation.ServiceActivator;
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;@ServiceActivatorpublic void processPayment(Payment payment) throws PaymentException {bankingService.pay(payment);}}

再次-注意@ServiceActivator批注。这意味着当服务激活器组件出现在游戏中时，Spring Integration应该调用相应的方法。要使用服务激活器，我们需要将其添加到集成模式中：

<int:service-activator input-channel='bankingChannel' ref='paymentProcessor'><int:poller fixed-rate='500' error-channel='failedPaymentsChannel' />
</int:service-activator><int:channel id = 'failedPaymentsChannel' />

请注意，我们正在定义固定速率属性，这意味着将每半秒调用一次激活器（如果BankingChannel中存在某些消息）。我们还定义了错误通道属性，但是我们很快就会到达那里。

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。 Spring Integration提供了一种称为“错误通道”的技术，我们可以（显然）从系统发送错误消息。错误通道只是另一个通道，当此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。在上一个组件（服务激活器）中，我们指定了error-channel属性来引用failedPaymentsChannel 。当消息到达此通道时，我们将调用另一个服务激活器并打印出错误。这是FailedPaymentHandler服务激活器的实现：

package com.vrtoonjava.invoices;import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.stereotype.Component;@Component
public class FailedPaymentHandler {@ServiceActivatorpublic void handleFailedPayment(Exception e) {System.out.println('Payment failed: ' + e);// now the system should do something reasonable, like retrying the payment// omitted for the tutorial purposes}}

然后像往常一样将其连接到集成模式：

<int:service-activatorinput-channel='failedPaymentsChannel'ref='failedPaymentHandler' />

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.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;/*** Job that every n-seconds generates invoices and sends them to the system.* In real world this might be endpoint receiving invoices from another system.*/
@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 = 'invoices-int-schema.xml' /><context:component-scan base-package = 'com.vrtoonjava.invoices' /><context:component-scan base-package = 'com.vrtoonjava.banking' /><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
Amount of $3441 can be automatically processed by system
Amount of $17419 can not be automatically processed by system
Processing payment Payment{senderAccount=current-local-acc, receiverAccount=test-account 1011000, dollars=3441}
Amount of $18442 can not be automatically processed by system
Amount of $19572 can not be automatically processed by system
Amount of $5471 can be automatically processed by system
Amount of $1663 can be automatically processed by system
Processing payment Payment{senderAccount=current-iban-acc, receiverAccount=test-iban-2211000, dollars=5471}
Amount of $13160 can not be automatically processed by system
Amount of $2213 can be automatically processed by system
Amount of $1423 can be automatically processed by system
Processing payment Payment{senderAccount=current-iban-acc, receiverAccount=test-iban-8051000, dollars=1663}
Amount of $1267 can be automatically processed by system
Payment failed: org.springframework.integration.MessageHandlingException: com.vrtoonjava.banking.PaymentException: Banking services are offline, try again later!
Processing payment Payment{senderAccount=current-iban-acc, receiverAccount=test-iban-6141000, dollars=1423}
Processing payment Payment{senderAccount=current-local-acc, receiverAccount=test-account 6761000, dollars=1267}

参考： Spring Integration –从头开始的应用程序，来自我们的JCG合作伙伴 Michal Vrtiak的第2部分，在vrtoonjava博客上。