improve logger command error message. #1077

core/src/main/java/com/taobao/arthas/core/command/logger/LoggerCommand.java

@@ -39,10 +39,16 @@ import com.taobao.text.util.RenderUtil;
  * @author hengyunabc 2019-09-04
  *
  */
+//@formatter:off
 @Name("logger")
 @Summary("Print logger info, and update the logger level")
-@Description("\nExamples:\n" + "  logger\n" + "  logger -c 327a647b\n"
-                + "  logger -c 327a647b --name ROOT --level debug\n" + Constants.WIKI + Constants.WIKI_HOME + "logger")
+@Description("\nExamples:\n"
+                + "  logger\n"
+                + "  logger -c 327a647b\n"
+                + "  logger -c 327a647b --name ROOT --level debug\n"
+                + "  logger --include-no-appender\n"
+                + Constants.WIKI + Constants.WIKI_HOME + "logger")
+//@formatter:on
 public class LoggerCommand extends AnnotatedCommand {
     private static final Logger logger = LogUtil.getArthasLogger();
 
@@ -159,9 +165,9 @@ public class LoggerCommand extends AnnotatedCommand {
         }
 
         if (result) {
-            process.write("update logger level success.\n");
+            process.write("Update logger level success.\n");
         } else {
-            process.write("update logger level fail.\n");
+            process.write("Update logger level fail. Try to specify the classloader with the -c option. Use `sc -d CLASSNAME` to find out the classloader hashcode.\n");
         }
     }
 

site/src/site/sphinx/en/logger.md

@@ -130,6 +130,16 @@ In the `appenders` section:
 update logger level success.
 ```
 
+#### 指定classloader更新 logger level
+
+默认情况下，logger命令会在SystemClassloader下执行，如果应用是传统的`war`应用，或者spring boot fat jar启动的应用，那么需要指定classloader。
+
+可以先用 `sc -d yourClassName` 来查看具体的 classloader hashcode，然后在更新level时指定classloader：
+
+```bash
+[arthas@2062]$ logger -c 2a139a55 --name ROOT --level debug
+```
+
 #### View the logger information without appenders
 
 

site/src/site/sphinx/logger.md

@@ -131,6 +131,16 @@ logger
 update logger level success.
 ```
 
+#### 指定classloader更新 logger level
+
+默认情况下，logger命令会在SystemClassloader下执行，如果应用是传统的`war`应用，或者spring boot fat jar启动的应用，那么需要指定classloader。
+
+可以先用 `sc -d yourClassName` 来查看具体的 classloader hashcode，然后在更新level时指定classloader：
+
+```bash
+[arthas@2062]$ logger -c 2a139a55 --name ROOT --level debug
+```
+
 #### 查看没有appender的logger的信息