chore(spring-boot-starter): Add Spring Boot External Client Config

- Validate against misusing orderByCreateTime and useCreateTime configurations together
- Validate against wrong orderByCreateTime values

spring-boot-starter/starter-client/spring/src/main/java/org/camunda/bpm/client/spring/annotation/EnableExternalTaskClient.java

@@ -49,6 +49,9 @@
   long LONG_NULL_VALUE = Long.MIN_VALUE;
   int INT_NULL_VALUE = Integer.MIN_VALUE;
 
+  String STRING_ORDER_BY_ASC_VALUE = "asc";
+  String STRING_ORDER_BY_DESC_VALUE = "desc";
+
   /**
    * Base url of the Camunda Runtime Platform REST API. This information is mandatory.
    * Alias of {@link #baseUrl()}.
@@ -94,6 +97,22 @@
    */
   boolean usePriority() default true;
 
+  /**
+   * Specifies whether tasks should be fetches based on their createTime or arbitrarily.
+   * This information is optional. Default is <code>false</code>.
+   *
+   * @return useCreateTime when fetching and locking tasks
+   */
+  boolean useCreateTime() default false;
+
+  /**
+   * Specifies whether tasks should be fetched based on their createTime with a configured order ()
+   * This information is optional.
+   *
+   * @return useCreateTime when fetching and locking tasks
+   */
+  String orderByCreateTime() default STRING_NULL_VALUE;
+
   /**
    * Asynchronous response (long polling) is enabled if a timeout is given.
    * Specifies the maximum waiting time for the response of fetched and locked external tasks.

spring-boot-starter/starter-client/spring/src/main/java/org/camunda/bpm/client/spring/impl/client/ClientConfiguration.java

@@ -16,18 +16,20 @@
  */
 package org.camunda.bpm.client.spring.impl.client;
 
-import org.camunda.bpm.client.spring.annotation.EnableExternalTaskClient;
-
 import static org.camunda.bpm.client.spring.annotation.EnableExternalTaskClient.INT_NULL_VALUE;
 import static org.camunda.bpm.client.spring.annotation.ExternalTaskSubscription.LONG_NULL_VALUE;
-import static org.camunda.bpm.client.spring.annotation.ExternalTaskSubscription.STRING_NULL_VALUE;
+
+import org.camunda.bpm.client.spring.annotation.EnableExternalTaskClient;
+import org.camunda.bpm.client.spring.annotation.ExternalTaskSubscription;
 
 public class ClientConfiguration {
 
   protected String baseUrl;
   protected String workerId;
   protected Integer maxTasks;
   protected Boolean usePriority;
+  protected Boolean useCreateTime;
+  protected String orderByCreateTime;
   protected String defaultSerializationFormat;
   protected String dateFormat;
   protected Long asyncResponseTimeout;
@@ -99,6 +101,22 @@ public void setUsePriority(Boolean usePriority) {
     this.usePriority = usePriority;
   }
 
+  public String getOrderByCreateTime() {
+    return orderByCreateTime;
+  }
+
+  public void setOrderByCreateTime(String orderByCreateTime) {
+    this.orderByCreateTime = orderByCreateTime;
+  }
+
+  public Boolean getUseCreateTime() {
+    return useCreateTime;
+  }
+
+  public void setUseCreateTime(Boolean useCreateTime) {
+    this.useCreateTime = useCreateTime;
+  }
+
   public Boolean getDisableAutoFetching() {
     return disableAutoFetching;
   }
@@ -127,6 +145,9 @@ public void fromAnnotation(EnableExternalTaskClient annotation) {
 
     setUsePriority(annotation.usePriority());
 
+    setUseCreateTime(annotation.useCreateTime());
+    configureOrderByCreateTime(annotation);
+
     long asyncResponseTimeout = annotation.asyncResponseTimeout();
     setAsyncResponseTimeout(isNull(asyncResponseTimeout) ? null : asyncResponseTimeout);
 
@@ -144,8 +165,16 @@ public void fromAnnotation(EnableExternalTaskClient annotation) {
     setDefaultSerializationFormat(isNull(serializationFormat) ? null : serializationFormat);
   }
 
+  protected void configureOrderByCreateTime(EnableExternalTaskClient annotation) {
+    if (EnableExternalTaskClient.STRING_NULL_VALUE.equals(annotation.orderByCreateTime())) {
+      setOrderByCreateTime(null);
+    } else {
+      setOrderByCreateTime(annotation.orderByCreateTime());
+    }
+  }
+
   protected static boolean isNull(String value) {
-    return STRING_NULL_VALUE.equals(value);
+    return ExternalTaskSubscription.STRING_NULL_VALUE.equals(value);
   }
 
   protected static boolean isNull(long value) {

spring-boot-starter/starter-client/spring/src/main/java/org/camunda/bpm/client/spring/impl/client/ClientFactory.java

@@ -16,6 +16,9 @@
  */
 package org.camunda.bpm.client.spring.impl.client;
 
+import static org.camunda.bpm.client.spring.annotation.EnableExternalTaskClient.STRING_ORDER_BY_ASC_VALUE;
+import static org.camunda.bpm.client.spring.annotation.EnableExternalTaskClient.STRING_ORDER_BY_DESC_VALUE;
+
 import java.util.ArrayList;
 import java.util.List;
 
@@ -89,6 +92,9 @@ public ExternalTaskClient getObject() {
       if (backoffStrategy != null) {
         clientBuilder.backoffStrategy(backoffStrategy);
       }
+
+      tryConfigureCreateTimeOrder(clientBuilder);
+
       client = clientBuilder.build();
     }
 
@@ -101,6 +107,51 @@ protected void addClientRequestInterceptors(ExternalTaskClientBuilder taskClient
     requestInterceptors.forEach(taskClientBuilder::addInterceptor);
   }
 
+  protected void tryConfigureCreateTimeOrder(ExternalTaskClientBuilder builder) {
+    checkForCreateTimeMisconfiguration();
+
+    if (isUseCreateTimeEnabled()) {
+      builder.orderByCreateTime().desc();
+      return;
+    }
+
+    if (isOrderByCreateTimeEnabled()) {
+      handleOrderByCreateTimeConfig(builder);
+    }
+  }
+
+  protected void handleOrderByCreateTimeConfig(ExternalTaskClientBuilder builder) {
+    String orderByCreateTime = clientConfiguration.getOrderByCreateTime();
+
+    if (STRING_ORDER_BY_ASC_VALUE.equals(orderByCreateTime)) {
+      builder.orderByCreateTime().asc();
+      return;
+    }
+
+    if (STRING_ORDER_BY_DESC_VALUE.equals(orderByCreateTime)) {
+      builder.orderByCreateTime().desc();
+      return;
+    }
+
+    throw new IllegalArgumentException("Invalid value " + clientConfiguration.getOrderByCreateTime()
+        + ". Please use either \"asc\" or \"desc\" value for configuring \"orderByCreateTime\" on the client");
+  }
+
+  protected boolean isOrderByCreateTimeEnabled() {
+    return clientConfiguration.getOrderByCreateTime() != null;
+  }
+
+  protected boolean isUseCreateTimeEnabled() {
+    return clientConfiguration.getUseCreateTime() != null && clientConfiguration.getUseCreateTime();
+  }
+
+  protected void checkForCreateTimeMisconfiguration() {
+    if (isUseCreateTimeEnabled() && isOrderByCreateTimeEnabled()) {
+      throw new IllegalStateException(
+          "Both \"useCreateTime\" and \"orderByCreateTime\" are enabled. Please use one or the other");
+    }
+  }
+
   @Autowired(required = false)
   public void setRequestInterceptors(List<ClientRequestInterceptor> requestInterceptors) {
     if (requestInterceptors != null) {

spring-boot-starter/starter-client/spring/src/test/java/org/camunda/bpm/client/spring/ConfigurationTest.java

@@ -16,22 +16,23 @@
  */
 package org.camunda.bpm.client.spring;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.when;
+
+import java.util.HashMap;
+import java.util.Map;
 import org.camunda.bpm.client.spring.configuration.FullConfiguration;
 import org.camunda.bpm.client.task.ExternalTaskHandler;
+import org.junit.Before;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ContextConfiguration;
 
-import java.util.HashMap;
-import java.util.Map;
-
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.verifyNoMoreInteractions;
-
 @ContextConfiguration(classes = {FullConfiguration.class})
 @DirtiesContext // context cannot be reused since the mocks need to be reinitialized completely
 public class ConfigurationTest extends MockedTest {
@@ -40,6 +41,12 @@ public class ConfigurationTest extends MockedTest {
   @Qualifier("handler")
   protected ExternalTaskHandler handler;
 
+  @Before
+  public void init() {
+    when(clientBuilder.orderByCreateTime()).thenReturn(clientBuilder);
+    when(clientBuilder.asc()).thenReturn(clientBuilder);
+  }
+
   @Test
   public void shouldVerifyClientConfiguration() {
     verify(clientBuilder).baseUrl("url");
@@ -52,7 +59,10 @@ public void shouldVerifyClientConfiguration() {
     verify(clientBuilder).lockDuration(4444);
     verify(clientBuilder).dateFormat("date-format");
     verify(clientBuilder).defaultSerializationFormat("default-serialization-format");
+    verify(clientBuilder).orderByCreateTime();
+    verify(clientBuilder).asc();
     verify(clientBuilder).build();
+
     verifyNoMoreInteractions(clientBuilder);
   }
 

spring-boot-starter/starter-client/spring/src/test/java/org/camunda/bpm/client/spring/DefaultConfigurationTest.java

@@ -48,6 +48,8 @@ public void shouldVerifyClientDefaults() {
     verify(clientBuilder, never()).workerId(anyString());
     verify(clientBuilder, never()).maxTasks(anyInt());
     verify(clientBuilder, never()).usePriority(anyBoolean());
+    verify(clientBuilder, never()).useCreateTime(anyBoolean());
+    verify(clientBuilder, never()).orderByCreateTime();
     verify(clientBuilder, never()).asyncResponseTimeout(anyLong());
     verify(clientBuilder, never()).disableAutoFetching();
     verify(clientBuilder, never()).disableBackoffStrategy();

spring-boot-starter/starter-client/spring/src/test/java/org/camunda/bpm/client/spring/MockedTest.java

@@ -16,6 +16,13 @@
  */
 package org.camunda.bpm.client.spring;
 
+import static org.junit.Assume.assumeTrue;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.RETURNS_SELF;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.when;
+
 import org.camunda.bpm.client.ExternalTaskClient;
 import org.camunda.bpm.client.ExternalTaskClientBuilder;
 import org.camunda.bpm.client.topic.TopicSubscription;
@@ -29,13 +36,6 @@
 import org.mockito.junit.MockitoRule;
 import org.springframework.test.context.junit4.SpringRunner;
 
-import static org.junit.Assume.assumeTrue;
-import static org.mockito.ArgumentMatchers.anyString;
-import static org.mockito.Mockito.RETURNS_SELF;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.mockStatic;
-import static org.mockito.Mockito.when;
-
 @RunWith(SpringRunner.class)
 public abstract class MockedTest {
 

spring-boot-starter/starter-client/spring/src/test/java/org/camunda/bpm/client/spring/configuration/FullConfiguration.java

@@ -30,6 +30,8 @@
     maxTasks = 1111,
     workerId = "worker-id",
     usePriority = false,
+    useCreateTime = false,
+    orderByCreateTime = "asc",
     asyncResponseTimeout = 5555,
     disableAutoFetching = true,
     disableBackoffStrategy = true,