Support configure preference for single config

Add log info.

spring-cloud-alibaba-examples/nacos-example/nacos-config-preference-example/readme-zh.md

@@ -8,15 +8,37 @@
 
 1. 启动一个 Nacos server  
 添加配置 `test.yml`
-
 ```yaml
 configdata:
   user:
     name: freeman
 ```
 
-2. 设置配置偏好 `spring.cloud.nacos.config.preference=remote`
+添加配置 `test2.yml`
+```yaml
+dev:
+  age: 22
+```
+
+2. 设置配置偏好
+
+设置默认配置偏好 
+```yaml
+spring:
+  cloud:
+    nacos:
+      config:
+        preference: remote
+```
+
+指定配置（test2.yml）设置配置偏好
+```yaml
+spring:
+  config:
+    import:
+      - optional:nacos:test.yml
+      - optional:nacos:test2.yml?preference=local
+```
 
-3. 访问 `localhost`  
-应该能看到值为 `freeman`，因为优先使用了配置中心配置  
-修改配置为 `spring.cloud.nacos.config.preference=local` 那么值应该为 `aa`
+3. 验证
+访问 `localhost`，应该能看到值为 `freeman: 20`，因为 `name` 优先使用了配置中心配置，`age` 优先使用本地配置。  

spring-cloud-alibaba-examples/nacos-example/nacos-config-preference-example/readme.md

@@ -8,15 +8,37 @@ This project demonstrates how to use config preferences.
 
 1. Start a Nacos server
 add configuration `test.yml`
-
 ```yaml
 configdata:
   user:
     name: freeman
 ```
 
-2. Set config preference `spring.cloud.nacos.config.preference=remote`
+add configuration `test2.yml`
+```yaml
+dev:
+  age: 22
+```
+
+2. Set configuration preference
+
+Set default configuration preference
+```yaml
+spring:
+  cloud:
+    nacos:
+      config:
+        preference: remote
+```
+
+Specify configuration (test 2.yml) to set configuration preference
+```yaml
+spring:
+  config:
+    import:
+      - optional:nacos:test.yml
+      - optional:nacos:test2.yml?preference=local
+```
 
-3. access `localhost`  
-You should see a value of `freeman`, because the configuration center configuration is used first.  
-Modify the configuration to `spring.cloud.nacos.config.preference=local` then the value should be `aa`.
+3. Verify 
+Access `localhost`, you should see the value of `freeman: 20`, because `name` uses the configuration center configuration first, and `age` uses the local configuration first.

spring-cloud-alibaba-examples/nacos-example/nacos-config-preference-example/src/main/java/com/alibaba/cloud/configpreference/examples/controller/UserController.java

@@ -19,6 +19,8 @@ package com.alibaba.cloud.configpreference.examples.controller;
 import com.alibaba.cloud.configpreference.examples.model.UserProperties;
 
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.cloud.context.config.annotation.RefreshScope;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
@@ -28,14 +30,17 @@ import org.springframework.web.bind.annotation.RestController;
  * @author freeman
  */
 @RestController
+@RefreshScope
 public class UserController {
 
 	@Autowired
 	private UserProperties userProperties;
+	@Value("${dev.age}")
+	private int age;
 
 	@GetMapping
 	public String getName() {
-		return userProperties.getName();
+		return userProperties.getName() + ": " + age;
 	}
 
 }

spring-cloud-alibaba-examples/nacos-example/nacos-config-preference-example/src/main/resources/application.yml

@@ -12,6 +12,7 @@ spring:
   config:
     import:
       - optional:nacos:test.yml
+      - optional:nacos:test2.yml?preference=local
   profiles:
     active: dev
 
@@ -22,4 +23,6 @@ spring:
       on-profile: dev
 configdata:
   user:
-    name: bb
+    name: bb
+dev:
+  age: 20

spring-cloud-alibaba-starters/spring-cloud-starter-alibaba-nacos-config/src/main/java/com/alibaba/cloud/nacos/configdata/NacosConfigDataLoader.java

@@ -88,12 +88,10 @@ public class NacosConfigDataLoader implements ConfigDataLoader<NacosConfigDataRe
 
 			NacosPropertySourceRepository.collectNacosPropertySource(propertySource);
 
-			return new ConfigData(propertySources, getOptions(context));
+			return new ConfigData(propertySources, getOptions(context, resource));
 		}
 		catch (Exception e) {
-			if (log.isDebugEnabled()) {
-				log.debug("Error getting properties from nacos: " + resource, e);
-			}
+			log.warn("Error getting properties from nacos: " + resource, e);
 			if (!resource.isOptional()) {
 				throw new ConfigDataResourceNotFoundException(resource, e);
 			}
@@ -101,15 +99,12 @@ public class NacosConfigDataLoader implements ConfigDataLoader<NacosConfigDataRe
 		return null;
 	}
 
-	private Option[] getOptions(ConfigDataLoaderContext context) {
-		Binder binder = context.getBootstrapContext().get(Binder.class);
-		ConfigPreference preference = binder
-				.bind("spring.cloud.nacos.config.preference", ConfigPreference.class)
-				.orElse(LOCAL);
+	private Option[] getOptions(ConfigDataLoaderContext context,
+			NacosConfigDataResource resource) {
 		List<Option> options = new ArrayList<>();
 		options.add(IGNORE_IMPORTS);
 		options.add(IGNORE_PROFILES);
-		if (preference == REMOTE) {
+		if (getPreference(context, resource) == REMOTE) {
 			// mark it as 'PROFILE_SPECIFIC' config, it has higher priority,
 			// will override the none profile specific config.
 			// fixed https://github.com/alibaba/spring-cloud-alibaba/issues/2455
@@ -118,14 +113,48 @@ public class NacosConfigDataLoader implements ConfigDataLoader<NacosConfigDataRe
 		return options.toArray(new Option[0]);
 	}
 
+	private ConfigPreference getPreference(ConfigDataLoaderContext context,
+			NacosConfigDataResource resource) {
+		Binder binder = context.getBootstrapContext().get(Binder.class);
+		ConfigPreference preference = binder
+				.bind("spring.cloud.nacos.config.preference", ConfigPreference.class)
+				.orElse(LOCAL);
+		String specificPreference = resource.getConfig().getPreference();
+		if (specificPreference != null) {
+			try {
+				preference = ConfigPreference.valueOf(specificPreference.toUpperCase());
+			}
+			catch (IllegalArgumentException ignore) {
+				// illegal preference value, just ignore.
+				log.warn(String.format(
+						"illegal preference value: %s, using default preference: %s",
+						specificPreference, preference));
+			}
+		}
+		return preference;
+	}
+
 	private List<PropertySource<?>> pullConfig(ConfigService configService, String group,
 			String dataId, String suffix, long timeout)
 			throws NacosException, IOException {
 		String config = configService.getConfig(dataId, group, timeout);
+		logLoadInfo(group, dataId, config);
 		return NacosDataParserHandler.getInstance().parseNacosData(dataId, config,
 				suffix);
 	}
 
+	private void logLoadInfo(String group, String dataId, String config) {
+		if (config != null) {
+			log.info(String.format(
+					"[Nacos Config] Load config[dataId=%s, group=%s] success", dataId,
+					group));
+		}
+		else {
+			log.warn(String.format("[Nacos Config] config[dataId=%s, group=%s] is empty",
+					dataId, group));
+		}
+	}
+
 	protected <T> T getBean(ConfigDataLoaderContext context, Class<T> type) {
 		if (context.getBootstrapContext().isRegistered(type)) {
 			return context.getBootstrapContext().get(type);

spring-cloud-alibaba-starters/spring-cloud-starter-alibaba-nacos-config/src/main/java/com/alibaba/cloud/nacos/configdata/NacosConfigDataLocationResolver.java

@@ -67,6 +67,8 @@ public class NacosConfigDataLocationResolver
 
 	private static final String REFRESH_ENABLED = "refreshEnabled";
 
+	private static final String PREFERENCE = "preference";
+
 	public NacosConfigDataLocationResolver(Log log) {
 		this.log = log;
 	}
@@ -166,12 +168,17 @@ public class NacosConfigDataLocationResolver
 				location.isOptional(), profiles, log,
 				new NacosItemConfig().setGroup(groupFor(uri, properties))
 						.setDataId(dataIdFor(uri)).setSuffix(suffixFor(uri, properties))
-						.setRefreshEnabled(refreshEnabledFor(uri, properties)));
+						.setRefreshEnabled(refreshEnabledFor(uri, properties))
+						.setPreference(preferenceFor(uri)));
 		result.add(resource);
 
 		return result;
 	}
 
+	private String preferenceFor(URI uri) {
+		return getQueryMap(uri).get(PREFERENCE);
+	}
+
 	private URI getUri(ConfigDataLocation location, NacosConfigProperties properties) {
 		String path = location.getNonPrefixedValue(getPrefix());
 		if (StringUtils.isBlank(path)) {

spring-cloud-alibaba-starters/spring-cloud-starter-alibaba-nacos-config/src/main/java/com/alibaba/cloud/nacos/configdata/NacosConfigDataResource.java

@@ -105,16 +105,18 @@ public class NacosConfigDataResource extends ConfigDataResource {
 		private String dataId;
 		private String suffix;
 		private boolean refreshEnabled;
+		private String preference;
 
 		public NacosItemConfig() {
 		}
 
 		public NacosItemConfig(String group, String dataId, String suffix,
-				boolean refreshEnabled) {
+				boolean refreshEnabled, String preference) {
 			this.group = group;
 			this.dataId = dataId;
 			this.suffix = suffix;
 			this.refreshEnabled = refreshEnabled;
+			this.preference = preference;
 		}
 
 		public NacosItemConfig setGroup(String group) {
@@ -137,6 +139,11 @@ public class NacosConfigDataResource extends ConfigDataResource {
 			return this;
 		}
 
+		public NacosItemConfig setPreference(String preference) {
+			this.preference = preference;
+			return this;
+		}
+
 		public String getGroup() {
 			return group;
 		}
@@ -153,6 +160,10 @@ public class NacosConfigDataResource extends ConfigDataResource {
 			return refreshEnabled;
 		}
 
+		public String getPreference() {
+			return preference;
+		}
+
 		@Override
 		public boolean equals(Object o) {
 			if (this == o) {
@@ -165,19 +176,20 @@ public class NacosConfigDataResource extends ConfigDataResource {
 			return refreshEnabled == that.refreshEnabled
 					&& Objects.equals(group, that.group)
 					&& Objects.equals(dataId, that.dataId)
-					&& Objects.equals(suffix, that.suffix);
+					&& Objects.equals(suffix, that.suffix)
+					&& Objects.equals(preference, that.preference);
 		}
 
 		@Override
 		public int hashCode() {
-			return Objects.hash(group, dataId, suffix, refreshEnabled);
+			return Objects.hash(group, dataId, suffix, refreshEnabled, preference);
 		}
 
 		@Override
 		public String toString() {
 			return "NacosItemConfig{" + "group='" + group + '\'' + ", dataId='" + dataId
 					+ '\'' + ", suffix='" + suffix + '\'' + ", refreshEnabled="
-					+ refreshEnabled + '}';
+					+ refreshEnabled + ", preference=" + preference + '}';
 		}
 	}
 

spring-cloud-alibaba-starters/spring-cloud-starter-alibaba-nacos-config/src/main/java/com/alibaba/cloud/nacos/refresh/NacosContextRefresher.java

@@ -127,6 +127,8 @@ public class NacosContextRefresher
 				});
 		try {
 			configService.addListener(dataKey, groupKey, listener);
+			log.info("[Nacos Config] Listening config: dataId={}, group={}", dataKey,
+					groupKey);
 		}
 		catch (NacosException e) {
 			log.warn(String.format(