Allow PulsarTopicBuilder#init null values (#777)

* Allow PulsarTopicBuilder#init null values

See #756

* Clarify the deprecation of PulsarTopic.builder

Author: onobc

spring-pulsar-docs/src/main/antora/modules/ROOT/pages/whats-new.adoc

@@ -20,9 +20,9 @@ See xref:./reference/default-tenant-namespace.adoc[Default Tenant / Namespace] f
 Version `3.3.1` of the Pulsar client deprecates the `getPartitionsForTopic(java.lang.String)` in favor of `getPartitionsForTopic(java.lang.String, boolean metadataAutoCreationEnabled)`.
 
 ==== PulsarTopic#builder
-The `PulsarTopicBuilder` is now a registered bean that is configured with default values for domain, tenant, and namespace.
-As such, this convenience method is no longer needed.
-Instead, inject the builder bean where needed.
+When using Spring Boot the `PulsarTopicBuilder` is now a registered bean that is configured with default values for domain, tenant, and namespace.
+Therefore, if you are using Spring Boot, you can simply inject the builder where needed.
+Otherwise, use one of the `PulsarTopicBuilder` constructors directly.
 
 === Breaking Changes
 

spring-pulsar/src/main/java/org/springframework/pulsar/core/PulsarTopic.java

@@ -61,8 +61,9 @@ public record PulsarTopic(String topicName, int numberOfPartitions) {
 	 * Convenience method to create a topic builder with the specified topic name.
 	 * @param topicName the name of the topic
 	 * @return the topic builder instance
-	 * @deprecated As of version 1.2.0 topic builder is a registered bean - instead use an
-	 * injected instance where needed
+	 * @deprecated since 1.2.0 for removal in 1.4.0 in favor of
+	 * {@link PulsarTopicBuilder#PulsarTopicBuilder()} or
+	 * {@link PulsarTopicBuilder#PulsarTopicBuilder(TopicDomain, String, String)}
 	 */
 	@Deprecated(since = "1.2.0", forRemoval = true)
 	public static PulsarTopicBuilder builder(String topicName) {

spring-pulsar/src/main/java/org/springframework/pulsar/core/PulsarTopicBuilder.java

@@ -20,6 +20,7 @@
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 
 /**
  * Builder class to create {@link PulsarTopic} instances.
@@ -60,17 +61,18 @@ public PulsarTopicBuilder() {
 
 	/**
 	 * Create a builder instance that uses the specified defaults.
-	 * @param defaultDomain domain to use for the topic when not present in the name
-	 * @param defaultTenant tentant to use for the topic when not present in the name
-	 * @param defaultNamespace namespace to use for the topic when not present in the name
+	 * @param defaultDomain domain to use when topic name is not fully-qualified
+	 * @param defaultTenant tenant to use when topic name is not fully-qualified or null
+	 * to use the Pulsar default tenant of 'public'
+	 * @param defaultNamespace namespace to use when topic name is not fully-qualified or
+	 * null to use the Pulsar default namespace of 'namespace'
 	 */
-	public PulsarTopicBuilder(TopicDomain defaultDomain, String defaultTenant, String defaultNamespace) {
+	public PulsarTopicBuilder(TopicDomain defaultDomain, @Nullable String defaultTenant,
+			@Nullable String defaultNamespace) {
 		Assert.notNull(defaultDomain, "defaultDomain must not be null");
-		Assert.hasText(defaultTenant, "defaultTenant must be specified");
-		Assert.hasText(defaultNamespace, "defaultNamespace must be specified");
 		this.defaultDomain = defaultDomain;
-		this.defaultTenant = defaultTenant;
-		this.defaultNamespace = defaultNamespace;
+		this.defaultTenant = StringUtils.hasText(defaultTenant) ? defaultTenant : DEFAULT_TENANT;
+		this.defaultNamespace = StringUtils.hasText(defaultNamespace) ? defaultNamespace : DEFAULT_NAMESPACE;
 	}
 
 	/**

spring-pulsar/src/test/java/org/springframework/pulsar/core/PulsarTopicBuilderTests.java

@@ -80,4 +80,18 @@ private static Stream<Arguments> nameIsAlwaysFullyQualifiedProvider() {
 				Arguments.of(customBuilder, "persistent://foo/bar/my-topic", "persistent://foo/bar/my-topic"));
 	}
 
+	@Test
+	void whenConstructedWithNullTenantThenPulsarDefaultTenantIsUsed() {
+		var topicBuilder = new PulsarTopicBuilder(TopicDomain.persistent, null, "foo");
+		var fqTopic = topicBuilder.name("my-topic").build();
+		assertThat(fqTopic.topicName()).isEqualTo("persistent://public/foo/my-topic");
+	}
+
+	@Test
+	void whenConstructedWithNullNamespaceThenPulsarDefaultNamespaceIsUsed() {
+		var topicBuilder = new PulsarTopicBuilder(TopicDomain.persistent, "foo", null);
+		var fqTopic = topicBuilder.name("my-topic").build();
+		assertThat(fqTopic.topicName()).isEqualTo("persistent://foo/default/my-topic");
+	}
+
 }