add more info about expand object

core/src/main/java/com/taobao/arthas/core/command/monitor200/WatchCommand.java

@@ -10,6 +10,7 @@ import com.taobao.arthas.core.shell.cli.CompletionUtils;
 import com.taobao.arthas.core.shell.command.CommandProcess;
 import com.taobao.arthas.core.util.SearchUtils;
 import com.taobao.arthas.core.util.matcher.Matcher;
+import com.taobao.arthas.core.view.ObjectView;
 import com.taobao.middleware.cli.annotations.Argument;
 import com.taobao.middleware.cli.annotations.DefaultValue;
 import com.taobao.middleware.cli.annotations.Description;
@@ -101,7 +102,7 @@ public class WatchCommand extends EnhancerCommand {
     }
 
     @Option(shortName = "x", longName = "expand")
-    @Description("Expand level of object (1 by default)")
+    @Description("Expand level of object (1 by default), the max value is " + ObjectView.MAX_DEEP)
     public void setExpand(Integer expand) {
         this.expand = expand;
     }

core/src/main/java/com/taobao/arthas/core/view/ObjectView.java

@@ -20,6 +20,7 @@ import static java.lang.String.format;
  * Created by vlinux on 15/5/20.
  */
 public class ObjectView implements View {
+    public static final int MAX_DEEP = 4;
     private static final Logger logger = LoggerFactory.getLogger(ObjectView.class);
     private final static int MAX_OBJECT_LENGTH = 10 * 1024 * 1024; // 10M
 
@@ -33,7 +34,7 @@ public class ObjectView implements View {
 
     public ObjectView(Object object, int deep, int maxObjectLength) {
         this.object = object;
-        this.deep = deep > 4 ? 4 : deep;
+        this.deep = deep > MAX_DEEP ? MAX_DEEP : deep;
         this.maxObjectLength = maxObjectLength;
     }
 

site/src/site/sphinx/en/watch.md

@@ -22,7 +22,7 @@ There are four different scenarios for `watch` command, which makes it rather co
 |[s]|when method exits normally|
 |[f]|when method exits (either succeed or fail with exceptions)|
 |[E]|turn on regex matching while the default is wildcard matching|
-|[x:]|the depth to print the specified property with default value: 1|
+|[x:]|the depth to print the specified property with default value: 1, the max value is 4|
 
 F.Y.I
 1. any valid OGNL expression as `"{params,returnObj}"` supported
@@ -178,7 +178,7 @@ ts=2018-12-03 19:34:19; [cost=0.587833ms] result=@ArrayList[
 ```
 
 * `-x`: Expand level of object (1 by default)
-
+* The max value of `-x` is 4, to prevent the expansion result taking up too much memory. Users can specify the field in the `ognl` expression.
 #### Use condition expressions to locate specific call
 
 ```bash

site/src/site/sphinx/watch.md

@@ -22,7 +22,7 @@ watch 的参数比较多，主要是因为它能在 4 个不同的场景观察
 |[s]|在**函数返回之后**观察|
 |[f]|在**函数结束之后**(正常返回和异常返回)观察|
 |[E]|开启正则表达式匹配，默认为通配符匹配|
-|[x:]|指定输出结果的属性遍历深度，默认为 1|
+|[x:]|指定输出结果的属性遍历深度，默认为 1，最大值是4|
 
 这里重点要说明的是观察表达式，观察表达式的构成主要由 ognl 表达式组成，所以你可以这样写`"{params,returnObj}"`，只要是一个合法的 ognl 表达式，都能被正常支持。
 
@@ -178,6 +178,7 @@ ts=2018-12-03 19:34:19; [cost=0.587833ms] result=@ArrayList[
 ```
 
 * `-x`表示遍历深度，可以调整来打印具体的参数和结果内容，默认值是1。
+* `-x`最大值是4，防止展开结果占用太多内存。用户可以在`ognl`表达式里指定更具体的field。
 
 #### 条件表达式的例子