Fix list property to be mutable

Closes gh-7045

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/elasticsearch/jest/JestProperties.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.elasticsearch.jest;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
@@ -33,7 +34,8 @@ public class JestProperties {
 	/**
 	 * Comma-separated list of the Elasticsearch instances to use.
 	 */
-	private List<String> uris = Collections.singletonList("http://localhost:9200");
+	private List<String> uris = new ArrayList<String>(Collections.singletonList(
+			"http://localhost:9200"));
 
 	/**
 	 * Login user.

spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -108,6 +108,10 @@
     "description": "Enable Solr repositories.",
     "defaultValue": true
   },
+  {
+    "name": "spring.elasticsearch.jest.uris",
+    "defaultValue": ["http://localhost:9200"]
+  },
   {
     "name": "spring.http.encoding.enabled",
     "type": "java.lang.Boolean",

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/elasticsearch/jest/JestAutoConfigurationTests.java

@@ -73,7 +73,7 @@ public class JestAutoConfigurationTests {
 	@Test
 	public void customJestClient() {
 		load(CustomJestClient.class,
-				"spring.elasticsearch.jest.uris=http://localhost:9200");
+				"spring.elasticsearch.jest.uris[0]=http://localhost:9200");
 		assertThat(this.context.getBeansOfType(JestClient.class)).hasSize(1);
 	}