加载一个外部class到jvm中

Arthas可以通过redefine和retransform命令重新加载类， 那么如何加载一个外部class到jvm中呢？

考虑通过ClassLoader实例直接加载编译后的class文件字节码实现。

java代码

public class Person {
    String name;
    Integer age;
    
    // 省略getter/setter
}

加载过程

使用ArthasClassloader加载class文件字节码到ClassLoader中

# 内存编译java为class文件
[arthas@16936]$ mc /tmp/Person.java -d /tmp
Memory compiler output:
C:\tmp\Person.class

# 借助vmtool获得ArthasClassloader实例加载类
[arthas@16936]$ vmtool -a getInstances --className com.taobao.arthas.agent.ArthasClassloader --express '#path=@java.nio.file.Paths@get(new java.net.URI("file:///C:/tmp/Person.class")),#bytes=@java.nio.file.Files@readAllBytes(#path),instances[0].defineClass("Person", #bytes, 0, #bytes.length)'
@Class[
    ANNOTATION=@Integer[8192],
    ENUM=@Integer[16384],
    SYNTHETIC=@Integer[4096],
    cachedConstructor=null,
    newInstanceCallerCache=null,
    name=null,
    allPermDomain=@ProtectionDomain[ProtectionDomain  null
 null
 <no principals>
 java.security.Permissions@65f9cc2 (
 ("java.security.AllPermission" "<all permissions>" "<all actions>")
)

],
    useCaches=@Boolean[true],
    reflectionData=null,
    classRedefinedCount=@Integer[0],
    genericInfo=null,
    serialVersionUID=@Long[3206093459760846163],
    serialPersistentFields=@ObjectStreamField[][isEmpty=true;size=0],
    reflectionFactory=@ReflectionFactory[sun.reflect.ReflectionFactory@9fe6d14],
    initted=@Boolean[true],
    enumConstants=null,
    enumConstantDirectory=null,
    annotationData=null,
    annotationType=null,
    classValueMap=null,
]
[arthas@16936]$ sc Person
Person
Affect(row-cnt:1) cost in 4 ms.
# 搜索类发现已经加载
[arthas@16936]$ sc Person -d
 class-info        Person
 code-source
 name              Person
 isInterface       false
 isAnnotation      false
 isEnum            false
 isAnonymousClass  false
 isArray           false
 isLocalClass      false
 isMemberClass     false
 isPrimitive       false
 isSynthetic       false
 simple-name       Person
 modifier          public
 annotation
 interfaces
 super-class       +-java.lang.Object
 class-loader      +-com.taobao.arthas.agent.ArthasClassloader@26d26e26
                     +-sun.misc.Launcher$ExtClassLoader@4554617c
 classLoaderHash   26d26e26

Affect(row-cnt:1) cost in 5 ms.

较为复杂的场景可参考