Modify some spell error and prompt error (#2488)

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/conf/Config.java

@@ -40,7 +40,7 @@ public class Config {
         public static String NAMESPACE = "";
 
         /**
-         * Application code is showed in skywalking-ui. Suggestion: set a unique name for each service,
+         * Service name is showed in skywalking-ui. Suggestion: set a unique name for each service,
          * service instance nodes share the same code
          */
         public static String SERVICE_NAME = "";

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/conf/SnifferConfigInitializer.java

@@ -54,11 +54,11 @@ public class SnifferConfigInitializer {
      * specified agent config path is not set , the agent will try to locate `agent.config`, which should be in the
      * /config dictionary of agent package.
      * <p>
-     * Also try to override the config by system.env and system.properties. All the keys in these two places should
-     * start with {@link #ENV_KEY_PREFIX}. e.g. in env `skywalking.agent.application_code=yourAppName` to override
-     * `agent.application_code` in config file.
+     * Also try to override the config by system.properties. All the keys in this place should
+     * start with {@link #ENV_KEY_PREFIX}. e.g. in env `skywalking.agent.service_name=yourAppName` to override
+     * `agent.service_name` in config file.
      * <p>
-     * At the end, `agent.application_code` and `collector.servers` must be not blank.
+     * At the end, `agent.service_name` and `collector.servers` must be not blank.
      */
     public static void initialize(String agentOptions) throws ConfigNotFoundException, AgentPackageNotFoundException {
         InputStreamReader configFileStream;
@@ -80,7 +80,7 @@ public class SnifferConfigInitializer {
         try {
             overrideConfigBySystemProp();
         } catch (Exception e) {
-            logger.error(e, "Failed to read the system env.");
+            logger.error(e, "Failed to read the system properties.");
         }
 
         if (!StringUtil.isEmpty(agentOptions)) {
@@ -95,10 +95,10 @@ public class SnifferConfigInitializer {
         }
 
         if (StringUtil.isEmpty(Config.Agent.SERVICE_NAME)) {
-            throw new ExceptionInInitializerError("`agent.service_code` is missing.");
+            throw new ExceptionInInitializerError("`agent.service_name` is missing.");
         }
         if (StringUtil.isEmpty(Config.Collector.BACKEND_SERVICE)) {
-            throw new ExceptionInInitializerError("`collector.direct_servers` and `collector.servers` cannot be empty at the same time.");
+            throw new ExceptionInInitializerError("`collector.backend_service` is missing.");
         }
 
         IS_INIT_COMPLETED = true;
@@ -149,12 +149,11 @@ public class SnifferConfigInitializer {
     }
 
     /**
-     * Override the config by system properties. The env key must start with `skywalking`, the reuslt should be as same
+     * Override the config by system properties. The property key must start with `skywalking`, the result should be as same
      * as in `agent.config`
      * <p>
-     * such as: Env key of `agent.application_code` shoule be `skywalking.agent.application_code`
+     * such as: Property key of `agent.service_name` should be `skywalking.agent.service_name`
      *
-     * @return the config file {@link InputStream}, or null if not needEnhance.
      */
     private static void overrideConfigBySystemProp() throws IllegalAccessException {
         Properties properties = new Properties();
@@ -162,8 +161,9 @@ public class SnifferConfigInitializer {
         Iterator<Map.Entry<Object, Object>> entryIterator = systemProperties.entrySet().iterator();
         while (entryIterator.hasNext()) {
             Map.Entry<Object, Object> prop = entryIterator.next();
-            if (prop.getKey().toString().startsWith(ENV_KEY_PREFIX)) {
-                String realKey = prop.getKey().toString().substring(ENV_KEY_PREFIX.length());
+            String key = prop.getKey().toString();
+            if (key.startsWith(ENV_KEY_PREFIX)) {
+                String realKey = key.substring(ENV_KEY_PREFIX.length());
                 properties.put(realKey, prop.getValue());
             }
         }
@@ -189,11 +189,11 @@ public class SnifferConfigInitializer {
 
                 return new InputStreamReader(new FileInputStream(configFile), "UTF-8");
             } catch (FileNotFoundException e) {
-                throw new ConfigNotFoundException("Fail to load agent.config", e);
+                throw new ConfigNotFoundException("Failed to load agent.config", e);
             } catch (UnsupportedEncodingException e) {
-                throw new ConfigReadFailedException("Fail to load agent.config", e);
+                throw new ConfigReadFailedException("Failed to load agent.config", e);
             }
         }
-        throw new ConfigNotFoundException("Fail to load agent config file.");
+        throw new ConfigNotFoundException("Failed to load agent.config.");
     }
 }

apm-sniffer/apm-agent/src/main/java/org/apache/skywalking/apm/agent/SkyWalkingAgent.java

@@ -40,7 +40,7 @@ import java.util.List;
 import static net.bytebuddy.matcher.ElementMatchers.*;
 
 /**
- * The main entrance of sky-waking agent, based on javaagent mechanism.
+ * The main entrance of sky-walking agent, based on javaagent mechanism.
  *
  * @author wusheng
  */