在开发软件时，我们想创建“ -spine ”：我看到了spine，可维护性spine，spine扩展，以及-目前的趋势-分解（如果需要，可以在mikroservisy上扩展整体功能）。添加到您最喜欢的'能力脊椎列表。“
这些“功能”中的大多数（甚至可能全部）与组件之间的纯依赖关系并驾齐驱。
如果一个组件依赖于所有其他组件，那么我们不知道更改一个组件会有什么副作用，这使得维护代码库变得困难，并且扩展和分解变得更加困难。
随着时间的流逝，代码库中组件的边界趋于模糊。不良的依存关系出现，这使得使用代码变得更加困难。这会带来各种不良后果。特别是，发展正在放缓。
如果我们正在处理跨越许多不同业务领域或“有限上下文”的整体代码库，以使用域驱动设计术语，则这一点尤为重要。
我们如何保护我们的代码库免受不必要的依赖？ 精心设计有限的上下文并始终遵守组件边界。 本文演示了一套在两种情况下都可以在使用Spring Boot时为您提供帮助的实践。
样例代码
本文随附GitHub上的示例工作代码 。
包私有可见性
什么有助于保持组件边界？可见度降低。
如果我们对“内部”类使用Package-Private可见性，则只有同一包中的类才可以访问。 这使得很难从程序包外部添加不需要的依赖项。
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billing
├── api
└── internal
├── batchjob
| └── internal
└── database
├── api
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database
├── api
| ├── + LineItem
| ├── + ReadLineItems
| └── + WriteLineItems
└── internal
└── o BillingDatabase+, public, o, package-private.
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class BillingDatabase implements WriteLineItems, ReadLineItems {
...
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@RequiredArgsConstructor
class LoadInvoiceDataBatchJob {
private final WriteLineItems writeLineItems;
@Scheduled(fixedRate = 5000)
void loadDataFromBillingSystem() {
...
writeLineItems.saveLineItems(items);
}
} , @Scheduled Spring, .
, billing:
billing
├── api
| ├── + Invoice
| └── + InvoiceCalculator
└── internal
├── batchjob
├── database
└── o BillingService
billing InvoiceCalculator Invoice. , InvoiceCalculator , BillingService . BillingService ReadLineItemsAPI - :
@Component
@RequiredArgsConstructor
class BillingService implements InvoiceCalculator {
private final ReadLineItems readLineItems;
@Override
public Invoice calculateInvoice(
Long userId,
LocalDate fromDate,
LocalDate toDate) {
List<LineItem> items = readLineItems.getLineItemsForUser(
userId,
fromDate,
toDate);
...
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Spring Boot
, Spring Java Config Configuration internal :
billing
└── internal
├── batchjob
| └── internal
| └── o BillingBatchJobConfiguration
├── database
| └── internal
| └── o BillingDatabaseConfiguration
└── o BillingConfiguration
Spring Spring .
database :
@Configuration
@EnableJpaRepositories
@ComponentScan
class BillingDatabaseConfiguration {
} @Configuration Spring, , Spring .
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@ComponentScan @Bean @Configuration.
database Spring Data JPA. @EnableJpaRepositories.
batchjob :
@Configuration
@EnableScheduling
@ComponentScan
class BillingBatchJobConfiguration {
} @EnableScheduling. , @Scheduled bean-LoadInvoiceDataBatchJob.
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@Configuration
@ComponentScan
class BillingConfiguration {
} @ComponentScan , @Configuration Spring bean-.
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@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface InternalPackage {
} package-info.java :
@InternalPackage
package io.reflectoring.boundaries.billing.internal.database.internal;
import io.reflectoring.boundaries.InternalPackage;, , .
, , :
class InternalPackageTests {
private static final String BASE_PACKAGE = "io.reflectoring";
private final JavaClasses analyzedClasses =
new ClassFileImporter().importPackages(BASE_PACKAGE);
@Test
void internalPackagesAreNotAccessedFromOutside() throws IOException {
List<String> internalPackages = internalPackages(BASE_PACKAGE);
for (String internalPackage : internalPackages) {
assertPackageIsNotAccessedFromOutside(internalPackage);
}
}
private List<String> internalPackages(String basePackage) {
Reflections reflections = new Reflections(basePackage);
return reflections.getTypesAnnotatedWith(InternalPackage.class).stream()
.map(c -> c.getPackage().getName())
.collect(Collectors.toList());
}
void assertPackageIsNotAccessedFromOutside(String internalPackage) {
noClasses()
.that()
.resideOutsideOfPackage(packageMatcher(internalPackage))
.should()
.dependOnClassesThat()
.resideInAPackage(packageMatcher(internalPackage))
.check(analyzedClasses);
}
private String packageMatcher(String fullyQualifiedPackage) {
return fullyQualifiedPackage + "..";
}
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private static final String BASE_PACKAGE = "io.reflectoring";
@Test
void internalPackagesAreNotAccessedFromOutside() throws IOException {
// make it refactoring-safe in case we're renaming the base package
assertPackageExists(BASE_PACKAGE);
List<String> internalPackages = internalPackages(BASE_PACKAGE);
for (String internalPackage : internalPackages) {
// make it refactoring-safe in case we're renaming the internal package
assertPackageIsNotAccessedFromOutside(internalPackage);
}
}
void assertPackageExists(String packageName) {
assertThat(analyzedClasses.containPackage(packageName))
.as("package %s exists", packageName)
.isTrue();
}
private List<String> internalPackages(String basePackage) {
...
}
void assertPackageIsNotAccessedFromOutside(String internalPackage) {
...
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