Classloader support matching classloader by class name. (#1428)

core/src/main/java/com/taobao/arthas/core/command/klass100/ClassLoaderCommand.java

@@ -13,6 +13,7 @@ import com.taobao.arthas.core.shell.command.AnnotatedCommand;
 import com.taobao.arthas.core.shell.command.CommandProcess;
 import com.taobao.arthas.core.shell.handlers.Handler;
 import com.taobao.arthas.core.util.ClassUtils;
+import com.taobao.arthas.core.util.ClassLoaderUtils;
 import com.taobao.arthas.core.util.ResultUtils;
 import com.taobao.arthas.core.util.affect.RowAffect;
 import com.taobao.middleware.cli.annotations.Description;
@@ -56,6 +57,7 @@ public class ClassLoaderCommand extends AnnotatedCommand {
     private Logger logger = LoggerFactory.getLogger(ClassLoaderCommand.class);
     private boolean isTree = false;
     private String hashCode;
+    private String classLoaderClass;
     private boolean all = false;
     private String resource;
     private boolean includeReflectionClassLoader = true;
@@ -71,6 +73,12 @@ public class ClassLoaderCommand extends AnnotatedCommand {
         isTree = tree;
     }
     
+    @Option(longName = "classLoaderClass")
+    @Description("The class name of the special class's classLoader.")
+    public void setClassLoaderClass(String classLoaderClass) {
+        this.classLoaderClass = classLoaderClass;
+    }
+
     @Option(shortName = "c", longName = "classloader")
     @Description("The hash code of the special ClassLoader")
     public void setHashCode(String hashCode) {
@@ -113,6 +121,25 @@ public class ClassLoaderCommand extends AnnotatedCommand {
         process.interruptHandler(new ClassLoaderInterruptHandler(this));
 
         Instrumentation inst = process.session().getInstrumentation();
+        
+        if (!all && hashCode == null && classLoaderClass != null) {
+            List<ClassLoader> matchedClassLoaders = ClassLoaderUtils.getClassLoaderByClassName(inst, classLoaderClass);
+            if (matchedClassLoaders.size() == 1) {
+                hashCode = "" + Integer.toHexString(matchedClassLoaders.get(0).hashCode());
+            } else if (matchedClassLoaders.size() > 1) {
+                Collection<ClassLoaderVO> classLoaderVOList = ClassUtils.createClassLoaderVOList(matchedClassLoaders);
+                ClassLoaderModel classloaderModel = new ClassLoaderModel()
+                        .setClassLoaderClass(classLoaderClass)
+                        .setMatchedClassLoaders(classLoaderVOList);
+                process.appendResult(classloaderModel);
+                process.end(-1, "Found more than one classloader by class name, please specify classloader with '-c <classloader hash>'");
+                return;
+            } else {
+                process.end(-1, "Can not find classloader by class name: " + classLoaderClass + ".");
+                return;
+            }
+        }
+
         if (all) {
             processAllClasses(process, inst);
         } else if (hashCode != null && resource != null) {

core/src/main/java/com/taobao/arthas/core/command/model/ClassLoaderModel.java

@@ -4,6 +4,7 @@ import com.taobao.arthas.core.command.klass100.ClassLoaderCommand.ClassLoaderSta
 
 import java.util.List;
 import java.util.Map;
+import java.util.Collection;
 
 /**
  * @author gongdewei 2020/4/21
@@ -20,6 +21,9 @@ public class ClassLoaderModel extends ResultModel {
 
     private Map<String, ClassLoaderStat> classLoaderStats;
 
+    private Collection<ClassLoaderVO> matchedClassLoaders;
+    private String classLoaderClass;
+
     public ClassLoaderModel() {
     }
 
@@ -90,4 +94,22 @@ public class ClassLoaderModel extends ResultModel {
         this.classLoaderStats = classLoaderStats;
         return this;
     }
+
+    public String getClassLoaderClass() {
+        return classLoaderClass;
+    }
+
+    public ClassLoaderModel setClassLoaderClass(String classLoaderClass) {
+        this.classLoaderClass = classLoaderClass;
+        return this;
+    }
+
+    public Collection<ClassLoaderVO> getMatchedClassLoaders() {
+        return matchedClassLoaders;
+    }
+
+    public ClassLoaderModel setMatchedClassLoaders(Collection<ClassLoaderVO> matchedClassLoaders) {
+        this.matchedClassLoaders = matchedClassLoaders;
+        return this;
+    }
 }

core/src/main/java/com/taobao/arthas/core/command/view/ClassLoaderView.java

@@ -22,6 +22,12 @@ public class ClassLoaderView extends ResultView<ClassLoaderModel> {
 
     @Override
     public void draw(CommandProcess process, ClassLoaderModel result) {
+        if (result.getMatchedClassLoaders() != null) {
+            process.write("Matched classloaders: \n");
+            drawClassLoaders(process, result.getMatchedClassLoaders(), false);
+            process.write("\n");
+            return;
+        }
         if (result.getClassSet() != null) {
             drawAllClasses(process, result.getClassSet());
         }

site/src/site/sphinx/classloader.md

@@ -16,6 +16,7 @@ classloader
 |[t]|打印所有ClassLoader的继承树|
 |[a]|列出所有ClassLoader加载的类，请谨慎使用|
 |`[c:]`|ClassLoader的hashcode|
+|`[classLoaderClass:]`|指定执行表达式的 ClassLoader 的 class name|
 |`[c: r:]`|用ClassLoader去查找resource|
 |`[c: load:]`|用ClassLoader去加载指定的类|
 
@@ -67,6 +68,18 @@ file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar
 Affect(row-cnt:9) cost in 3 ms.
 ```
 
+*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。
+
+对于只有唯一实例的ClassLoader可以通过class name指定，使用起来更加方便：
+
+```bash
+$ classloader --classLoaderClass sun.misc.Launcher$AppClassLoader
+file:/private/tmp/arthas-demo.jar
+file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar
+
+Affect(row-cnt:9) cost in 3 ms.
+```
+
 #### 使用ClassLoader去查找resource
 
 ```bash

site/src/site/sphinx/en/classloader.md

@@ -13,6 +13,7 @@ View hierarchy, urls and classes-loading info for the class-loaders.
 |[t]|print classloader's hierarchy|
 |[a]|list all the classes loaded by all the classloaders (use it with great caution since the output can be huge)|
 |[c:]|print classloader's hashcode|
+|`[classLoaderClass:]`| The class name of the ClassLoader that executes the expression. |
 |`[c: r:]`|using ClassLoader to search resource|
 |`[c: load:]`|using ClassLoader to load class|
 
@@ -64,6 +65,18 @@ file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar
 Affect(row-cnt:9) cost in 3 ms.
 ```
 
+Note that the hashcode changes, you need to check the current ClassLoader information first, and extract the hashcode corresponding to the ClassLoader.
+
+For ClassLoader with only unique instance, it can be specified by class name, which is more convenient to use:
+
+```bash
+$ classloader --classLoaderClass sun.misc.Launcher$AppClassLoader
+file:/private/tmp/arthas-demo.jar
+file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar
+
+Affect(row-cnt:9) cost in 3 ms.
+```
+
 #### Use the classloader to load resource
 
 ```bash