ognl command tutorial #847 (#1327)

site/src/site/sphinx/en/ognl.md

@@ -1,6 +1,8 @@
 ognl
 ===
 
+[`ognl` online tutorial](https://alibaba.github.io/arthas/arthas-tutorials?language=en&id=command-ognl)
+
 > Execute ognl expression.
 
 Since 3.0.5.

site/src/site/sphinx/ognl.md

@@ -1,6 +1,8 @@
 ognl
 ===
 
+[`ognl`在线教程](https://alibaba.github.io/arthas/arthas-tutorials?language=cn&id=command-ognl)
+
 > 执行ognl表达式
 
 从3.0.5版本增加

tutorials/katacoda/command-ognl-cn/arthas-boot.md

@@ -0,0 +1,16 @@
+
+
+
+
+在新的`Terminal 2`里，下载`arthas-boot.jar`，再用`java -jar`命令启动：
+
+`wget https://alibaba.github.io/arthas/arthas-boot.jar
+java -jar arthas-boot.jar`{{execute T2}}
+
+`arthas-boot`是`Arthas`的启动程序，它启动后，会列出所有的Java进程，用户可以选择需要诊断的目标进程。
+
+选择第一个进程，输入 `1`{{execute T2}} ，再`Enter/回车`：
+
+Attach成功之后，会打印Arthas LOGO。输入 `help`{{execute T2}} 可以获取到更多的帮助信息。
+
+![Arthas Boot](/arthas/scenarios/common-resources/assets/arthas-boot.png)

tutorials/katacoda/command-ognl-cn/case-logger-config-problem.md

@@ -0,0 +1,52 @@
+
+
+在这个案例里，展示排查logger冲突的方法。
+
+### 确认应用使用的logger系统
+
+以`UserController`为例，它使用的是slf4j api，但实际使用到的logger系统是logback。
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
+
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
+@Logger[
+    serialVersionUID=@Long[5454405123156820674],
+    FQCN=@String[ch.qos.logback.classic.Logger],
+    name=@String[com.example.demo.arthas.user.UserController],
+    level=null,
+    effectiveLevelInt=@Integer[20000],
+    parent=@Logger[Logger[com.example.demo.arthas.user]],
+    childrenList=null,
+    aai=null,
+    additive=@Boolean[true],
+    loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
+]
+```
+
+### 获取logback实际加载的配置文件
+
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '#map1=@org.slf4j.LoggerFactory@getLogger("root").loggerContext.objectMap, #map1.get("CONFIGURATION_WATCH_LIST")'`{{execute T2}}
+
+
+### 使用classloader命令查找可能存在的logger配置文件
+
+`classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r logback-spring.xml`{{execute T2}}
+
+```
+$ classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r logback-spring.xml
+ jar:file:/Users/hengyunabc/code/java/spring-boot-inside/demo-arthas-spring-boot/target/demo-arthas-spring-boot-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/logback-spring.xml
+
+Affect(row-cnt:1) cost in 13 ms.
+```
+可以知道加载的配置的具体来源。
+
+可以尝试加载容易冲突的文件：
+
+`classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r logback.xml`{{execute T2}}
+
+`classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r log4j.properties`{{execute T2}}
+
+

tutorials/katacoda/command-ognl-cn/case-ognl-update-logger-level.md

@@ -0,0 +1,66 @@
+
+
+在这个案例里，动态修改应用的Logger Level。
+
+
+### 查找UserController的ClassLoader
+
+`sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash`{{execute T2}}
+
+```bash
+$ sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash
+ classLoaderHash   1be6f5c3
+```
+
+### 用ognl获取logger
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
+@Logger[
+    serialVersionUID=@Long[5454405123156820674],
+    FQCN=@String[ch.qos.logback.classic.Logger],
+    name=@String[com.example.demo.arthas.user.UserController],
+    level=null,
+    effectiveLevelInt=@Integer[20000],
+    parent=@Logger[Logger[com.example.demo.arthas.user]],
+    childrenList=null,
+    aai=null,
+    additive=@Boolean[true],
+    loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
+]
+```
+
+可以知道`UserController@logger`实际使用的是logback。可以看到`level=null`，则说明实际最终的level是从`root` logger里来的。
+
+### 单独设置UserController的logger level
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger.setLevel(@ch.qos.logback.classic.Level@DEBUG)'`{{execute T2}}
+
+再次获取`UserController@logger`，可以发现已经是`DEBUG`了：
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
+@Logger[
+    serialVersionUID=@Long[5454405123156820674],
+    FQCN=@String[ch.qos.logback.classic.Logger],
+    name=@String[com.example.demo.arthas.user.UserController],
+    level=@Level[DEBUG],
+    effectiveLevelInt=@Integer[10000],
+    parent=@Logger[Logger[com.example.demo.arthas.user]],
+    childrenList=null,
+    aai=null,
+    additive=@Boolean[true],
+    loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
+]
+```
+
+### 修改logback的全局logger level
+
+通过获取`root` logger，可以修改全局的logger level：
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@org.slf4j.LoggerFactory@getLogger("root").setLevel(@ch.qos.logback.classic.Level@DEBUG)'`{{execute T2}}
+

tutorials/katacoda/command-ognl-cn/finish.md

@@ -0,0 +1,12 @@
+
+在“ognl”中，我们演示了了Arthas的ognl命令。如果有更多的技巧或者使用疑问，欢迎在Issue里提出。
+
+* Issues: https://github.com/alibaba/arthas/issues
+* 文档： https://alibaba.github.io/arthas
+
+
+如果您在使用Arthas，请让我们知道，您的使用对我们非常重要：[查看](https://github.com/alibaba/arthas/issues/111)
+
+欢迎关注公众号，获取Arthas项目的信息，源码分析，案例实践。
+
+![Arthas公众号](/arthas/scenarios/common-resources/assets/qrcode_gongzhonghao.jpg)

tutorials/katacoda/command-ognl-cn/index.json

@@ -0,0 +1,53 @@
+{
+  "title": "Arthas ognl",
+  "description": "Arthas ognl",
+  "difficulty": "入门者",
+  "time": "10-20 分钟",
+  "details": {
+    "steps": [
+      {
+        "title": "启动demo",
+        "text": "start-demo.md"
+      },
+      {
+        "title": "启动arthas-boot，help命令",
+        "text": "arthas-boot.md"
+      },
+      {
+        "title": "Ognl详解",
+        "text": "ognl.md"
+      },
+      {
+        "title": "案例: 动态更新应用Logger Level",
+        "text": "case-ognl-update-logger-level.md"
+      },
+      {
+        "title": "案例: 排查logger冲突问题",
+        "text": "case-logger-config-problem.md"
+      }
+    ],
+    "intro": {
+      "text": "intro.md"
+    },
+    "finish": {
+      "text": "finish.md"
+    },
+    "assets": {
+      "host01": []
+    }
+  },
+  "environment": {
+    "uilayout": "terminal",
+    "showdashboard": true,
+    "dashboards": [
+      {
+        "name": "Web Port 80",
+        "port": 80
+      }
+    ]
+  },
+  "backend": {
+    "imageid": "java",
+    "environmentsprotocol": "http"
+  }
+}

tutorials/katacoda/command-ognl-cn/intro.md

@@ -0,0 +1,23 @@
+
+
+
+![Arthas](https://alibaba.github.io/arthas/_images/arthas.png)
+
+`Arthas` 是Alibaba开源的Java诊断工具，深受开发者喜爱。在线排查问题，无需重启；动态跟踪Java代码；实时监控JVM状态。
+
+`Arthas` 支持JDK 6+，支持Linux/Mac/Windows，采用命令行交互模式，同时提供丰富的 `Tab` 自动补全功能，进一步方便进行问题的定位和诊断。
+
+当你遇到以下类似问题而束手无策时，Arthas可以帮助你解决：
+
+- 这个类从哪个 jar 包加载的？为什么会报各种类相关的 Exception？
+- 我改的代码为什么没有执行到？难道是我没 commit？分支搞错了？
+- 遇到问题无法在线上 debug，难道只能通过加日志再重新发布吗？
+- 线上遇到某个用户的数据处理有问题，但线上同样无法 debug，线下无法重现！
+- 是否有一个全局视角来查看系统的运行状况？
+- 有什么办法可以监控到JVM的实时运行状态？
+- 怎么快速定位应用的热点，生成火焰图？
+
+本教程会以一个普通的Spring Boot应用为例，演示ognl命令。
+
+* Github: https://github.com/alibaba/arthas
+* 文档: https://alibaba.github.io/arthas/

tutorials/katacoda/command-ognl-cn/ognl.md

@@ -0,0 +1,73 @@
+
+在Arthas里，有一个单独的`ognl`命令，可以动态执行代码。
+
+
+查看用法：`ognl --help`{{execute T2}}
+
+### 调用static函数
+
+`ognl '@java.lang.System@out.println("hello ognl")'`{{execute T2}}
+
+可以检查`Terminal 1`里的进程输出，可以发现打印出了`hello ognl`。
+
+
+### 查找UserController的ClassLoader
+
+`sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash`{{execute T2}}
+
+```bash
+$ sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash
+ classLoaderHash   1be6f5c3
+```
+
+注意hashcode是变化的，需要先查看当前的ClassLoader信息，提取对应ClassLoader的hashcode。
+
+如果你使用`-c`，你需要手动输入hashcode：`-c <hashcode>`
+
+```bash
+$ ognl -c 1be6f5c3 @com.example.demo.arthas.user.UserController@logger
+```
+
+对于只有唯一实例的ClassLoader可以通过`--classLoaderClass`指定class name，使用起来更加方便：
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader  @org.springframework.boot.SpringApplication@logger
+@Slf4jLocationAwareLog[
+    FQCN=@String[org.apache.commons.logging.LogAdapter$Slf4jLocationAwareLog],
+    name=@String[org.springframework.boot.SpringApplication],
+    logger=@Logger[Logger[org.springframework.boot.SpringApplication]],
+]
+```
+
+ `--classLoaderClass` 的值是ClassLoader的类名，只有匹配到唯一的ClassLoader实例时才能工作，目的是方便输入通用命令，而`-c <hashcode>`是动态变化的。
+
+### 获取静态类的静态字段
+
+获取`UserController`类里的`logger`字段：
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader @com.example.demo.arthas.user.UserController@logger`{{execute T2}}
+
+还可以通过`-x`参数控制返回值的展开层数。比如：
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -x 2 @com.example.demo.arthas.user.UserController@logger`{{execute T2}}
+
+### 执行多行表达式，赋值给临时变量，返回一个List
+
+`ognl '#value1=@System@getProperty("java.home"), #value2=@System@getProperty("java.runtime.name"), {#value1, #value2}'`{{execute T2}}
+
+```bash
+$ ognl '#value1=@System@getProperty("java.home"), #value2=@System@getProperty("java.runtime.name"), {#value1, #value2}'
+@ArrayList[
+    @String[/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre],
+    @String[Java(TM) SE Runtime Environment],
+]
+```
+
+### 更多
+
+在Arthas里`ognl`表达式是很重要的功能，在很多命令里都可以使用`ognl`表达式。
+
+一些更复杂的用法，可以参考：
+
+* OGNL特殊用法请参考：https://github.com/alibaba/arthas/issues/71
+* OGNL表达式官方指南：https://commons.apache.org/proper/commons-ognl/language-guide.html

tutorials/katacoda/command-ognl-cn/start-demo.md

@@ -0,0 +1,14 @@
+
+
+
+
+下载`demo-arthas-spring-boot.jar`，再用`java -jar`命令启动：
+
+`wget https://github.com/hengyunabc/spring-boot-inside/raw/master/demo-arthas-spring-boot/demo-arthas-spring-boot.jar
+java -jar demo-arthas-spring-boot.jar`{{execute T1}}
+
+`demo-arthas-spring-boot`是一个很简单的spring boot应用，源代码：[查看](https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-arthas-spring-boot)
+
+启动之后，可以访问80端口： https://[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com
+
+![Demo Web](/arthas/scenarios/common-resources/assets/demo-web.png)

tutorials/katacoda/command-ognl-en/arthas-boot.md

@@ -0,0 +1,16 @@
+
+
+
+
+In the new `Terminal 2`, download `arthas-boot.jar` and start with the `java -jar` command:
+
+`wget https://alibaba.github.io/arthas/arthas-boot.jar
+java -jar arthas-boot.jar`{{execute T2}}
+
+`arthas-boot` is the launcher for `Arthas`. It lists all the Java processes, and the user can select the target process to be diagnosed.
+
+Select the first process, type `1`{{execute T2}} ，then type `Enter`：
+
+After the Attach is successful, Arthas LOGO is printed. Enter `help`{{execute T2}} for more help.
+
+![Arthas Boot](/arthas/scenarios/common-resources/assets/arthas-boot.png)

tutorials/katacoda/command-ognl-en/case-logger-config-problem.md

@@ -0,0 +1,53 @@
+
+
+
+In this case, show how to troubleshoot logger conflicts.
+
+### View the logger system used by the app
+
+Take `UserController` as an example, it uses slf4j api, but the actual logger system used is logback.
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
+
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
+@Logger[
+    serialVersionUID=@Long[5454405123156820674],
+    FQCN=@String[ch.qos.logback.classic.Logger],
+    name=@String[com.example.demo.arthas.user.UserController],
+    level=null,
+    effectiveLevelInt=@Integer[20000],
+    parent=@Logger[Logger[com.example.demo.arthas.user]],
+    childrenList=null,
+    aai=null,
+    additive=@Boolean[true],
+    loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
+]
+```
+
+### Find the configuration file actually loaded by the logback
+
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '#map1=@org.slf4j.LoggerFactory@getLogger("root").loggerContext.objectMap, #map1.get("CONFIGURATION_WATCH_LIST")'`{{execute T2}}
+
+
+### Use the classloader command to find possible logger configuration files
+
+`classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r logback-spring.xml`{{execute T2}}
+
+```
+$ classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r logback-spring.xml
+ jar:file:/Users/hengyunabc/code/java/spring-boot-inside/demo-arthas-spring-boot/target/demo-arthas-spring-boot-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/logback-spring.xml
+
+Affect(row-cnt:1) cost in 13 ms.
+```
+You can know the specific source of the loaded configuration.
+
+You can try to load files that are prone to conflict:
+
+`classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r logback.xml`{{execute T2}}
+
+`classloader --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -r log4j.properties`{{execute T2}}
+
+

tutorials/katacoda/command-ognl-en/case-ognl-update-logger-level.md

@@ -0,0 +1,64 @@
+
+In this case, show how to dynamically modify the Logger Level.
+
+### Find the ClassLoader of the UserController
+
+`sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash`{{execute T2}}
+
+```bash
+$ sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash
+ classLoaderHash   1be6f5c3
+```
+
+### Use ognl command to get the logger
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
+@Logger[
+    serialVersionUID=@Long[5454405123156820674],
+    FQCN=@String[ch.qos.logback.classic.Logger],
+    name=@String[com.example.demo.arthas.user.UserController],
+    level=null,
+    effectiveLevelInt=@Integer[20000],
+    parent=@Logger[Logger[com.example.demo.arthas.user]],
+    childrenList=null,
+    aai=null,
+    additive=@Boolean[true],
+    loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
+]
+```
+
+The user can know that `UserController@logger` actually uses logback. Because `level=null`, the actual final level is from the `root` logger.
+
+### Change the logger level of UserController
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger.setLevel(@ch.qos.logback.classic.Level@DEBUG)'`{{execute T2}}
+
+Get `UserController@logger` again, the user can see that it is already `DEBUG`:
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
+@Logger[
+    serialVersionUID=@Long[5454405123156820674],
+    FQCN=@String[ch.qos.logback.classic.Logger],
+    name=@String[com.example.demo.arthas.user.UserController],
+    level=@Level[DEBUG],
+    effectiveLevelInt=@Integer[10000],
+    parent=@Logger[Logger[com.example.demo.arthas.user]],
+    childrenList=null,
+    aai=null,
+    additive=@Boolean[true],
+    loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
+]
+```
+
+### Change the global logger level of the logback
+
+By getting the `root` logger, the user can modify the global logger level:
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@org.slf4j.LoggerFactory@getLogger("root").setLevel(@ch.qos.logback.classic.Level@DEBUG)'`{{execute T2}}
+

tutorials/katacoda/command-ognl-en/finish.md

@@ -0,0 +1,8 @@
+
+The `ognl Tutorial` demonstrates the usage of ognl. If you have more tips or questions, please feel free to ask in Issue.
+
+* Issues: https://github.com/alibaba/arthas/issues
+* Documentation: https://alibaba.github.io/arthas
+
+
+If you are using Arthas, please let us know. Your use is very important to us: [View](https://github.com/alibaba/arthas/issues/111)

tutorials/katacoda/command-ognl-en/index.json

@@ -0,0 +1,53 @@
+{
+  "title": "ognl",
+  "description": "ognl",
+  "difficulty": "master",
+  "time": "10-20 minutes",
+  "details": {
+    "steps": [
+      {
+        "title": "Start demo",
+        "text": "start-demo.md"
+      },
+      {
+        "title": "Start arthas-boot",
+        "text": "arthas-boot.md"
+      },
+      {
+        "title": "ognl Details",
+        "text": "ognl.md"
+      },
+      {
+        "title": "Case: Change Logger Level",
+        "text": "case-ognl-update-logger-level.md"
+      },
+      {
+        "title": "Case: Troubleshoot logger conflicts",
+        "text": "case-logger-config-problem.md"
+      }
+    ],
+    "intro": {
+      "text": "intro.md"
+    },
+    "finish": {
+      "text": "finish.md"
+    },
+    "assets": {
+      "host01": []
+    }
+  },
+  "environment": {
+    "uilayout": "terminal",
+    "showdashboard": true,
+    "dashboards": [
+      {
+        "name": "Web Port 80",
+        "port": 80
+      }
+    ]
+  },
+  "backend": {
+    "imageid": "java",
+    "environmentsprotocol": "http"
+  }
+}

tutorials/katacoda/command-ognl-en/intro.md

@@ -0,0 +1,40 @@
+
+
+
+![Arthas](https://alibaba.github.io/arthas/_images/arthas.png)
+
+`Arthas` is a Java diagnostic tool open-sourced by Alibaba middleware team. Arthas helps developers in trouble-shooting issues in production environment for Java based applications without modifying code or restarting servers.
+
+`Arthas` supports JDK 6+, supports Linux/Mac/Windows.
+
+## Background
+
+Oftentimes the production system network is inaccessible from local development environment. If issues are encountered in production systems, it is impossible to use IDE to debug the application remotely. What’s even worse, debugging in production environment is unacceptable, as it will suspend all the threads, leading to services downtime.
+
+Developers could always try to reproduce the same issue on the test/staging environment. However, this is tricky as some issues cannot be reproduced easily in a different environment, or even disappear once restarted.
+
+And if you’re thinking of adding some logs to your code to help trouble-shoot the issue, you will have to go through the following lifecycle: test, staging, and then to production. Time is money! This approach is inefficient! Worse still, the issue may not be fixed since it might be irreproducible once the JVM is restarted, as described above.
+
+Arthas is built to solve these issues. A developer can troubleshoot production issues on the fly. No JVM restart, no additional code changes. Arthas works as an observer, that is, it will never suspend your running threads.
+
+## Key features
+
+- Check whether a class is loaded? Or where the class is loaded from? (Useful for trouble-shooting jar file conflicts)
+- Decompile a class to ensure the code is running as expected.
+- Check classloader statistics, e.g. the number of classloaders, the number of classes loaded per classloader, the classloader hierarchy, possible classloader leaks, etc.
+- Check the method invocation details, e.g. method parameter, returned values, exceptions and etc.
+- Check the stack trace of specified method invocation. This is useful when a developer wants to know the caller of the method.
+- Trace the method invocation to find slow sub-invocations.
+- Monitor method invocation statistics, e.g. QPS (Query Per Second), RT (Return Time), success rate and etc.
+- Monitor system metrics, thread states and CPU usage, GC statistics and etc.
+- Supports command line interactive mode, with auto-complete feature enabled.
+- Supports telnet and WebSocket, which enables both local and remote diagnostics with command line and browsers.
+- Supports profiler/Flame Graph
+- Supports JDK 6+
+- Supports Linux/Mac/Windows
+
+This tutorial takes a normal Spring Boot application as an example to demonstrate the the usage of ognl.
+
+* Github: https://github.com/alibaba/arthas
+* Docs: https://alibaba.github.io/arthas/
+

tutorials/katacoda/command-ognl-en/ognl.md

@@ -0,0 +1,73 @@
+
+The `ognl` command can execute code dynamically.
+
+Check the usage: `ognl --help`{{execute T2}}
+
+### Invoke the static method
+
+`ognl '@java.lang.System@out.println("hello ognl")'`{{execute T2}}
+
+You can check the output of the process in `Terminal 1`, and find that it displays `hello ognl`.
+
+### Find the ClassLoader of the UserController
+
+`sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash`{{execute T2}}
+
+```bash
+$ sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash
+ classLoaderHash   1be6f5c3
+```
+
+Please write down your classLoaderHash here since it's dynamic. In the case here, it's `1be6f5c3`.
+
+if you use`-c`, you have to manually type hashcode by `-c <hashcode>`.
+
+```bash
+$ ognl -c 1be6f5c3 @com.example.demo.arthas.user.UserController@logger
+```
+
+For classloader with only one instance, it can be specified by `--classLoaderClass` using class name, which is more convenient to use.
+
+```bash
+$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader  @org.springframework.boot.SpringApplication@logger
+@Slf4jLocationAwareLog[
+    FQCN=@String[org.apache.commons.logging.LogAdapter$Slf4jLocationAwareLog],
+    name=@String[org.springframework.boot.SpringApplication],
+    logger=@Logger[Logger[org.springframework.boot.SpringApplication]],
+]
+```
+
+The value of `--classloaderclass` is the class name of classloader. It can only work when it matches a unique classloader instance. The purpose is to facilitate the input of general commands. However, `-c <hashcode>` is dynamic.
+
+### Get static fields of static classes
+
+Get the `logger` field of the `UserController` class:
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader @com.example.demo.arthas.user.UserController@logger`{{execute T2}}
+
+Control the number of expansion layers of the return value with the `-x` parameter. such as:
+
+`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader -x 2 @com.example.demo.arthas.user.UserController@logger`{{execute T2}}
+
+### Execute multi-line expressions
+
+Return a list:
+
+`ognl '#value1=@System@getProperty("java.home"), #value2=@System@getProperty("java.runtime.name"), {#value1, #value2}'`{{execute T2}}
+
+```bash
+$ ognl '#value1=@System@getProperty("java.home"), #value2=@System@getProperty("java.runtime.name"), {#value1, #value2}'
+@ArrayList[
+    @String[/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre],
+    @String[Java(TM) SE Runtime Environment],
+]
+```
+
+### More
+
+The `ognl` expression in Arthas is an important feature, and the `ognl` expression can be used in many commands.
+
+For some more complicated usages, refer to:
+
+* For special usage of OGNL, please refer to: https://github.com/alibaba/arthas/issues/71
+* Official Guide to OGNL Expressions: https://commons.apache.org/proper/commons-ognl/language-guide.html

tutorials/katacoda/command-ognl-en/start-demo.md

@@ -0,0 +1,14 @@
+
+
+
+
+Download `demo-arthas-spring-boot.jar`, and start with `java -jar` command:
+
+`wget https://github.com/hengyunabc/spring-boot-inside/raw/master/demo-arthas-spring-boot/demo-arthas-spring-boot.jar
+java -jar demo-arthas-spring-boot.jar`{{execute T1}}
+
+`demo-arthas-spring-boot` is a simple Spring Boot demo, the source code here: [View](https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-arthas-spring-boot)
+
+After booting, access port 80: https://[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com
+
+![Demo Web](/arthas/scenarios/common-resources/assets/demo-web.png)