Java自帶的調試接口，常用於運行時字節碼注入。
javaagent為一至少聲明有Premain-Class或Agent-Class屬性的jar，Premain-Class與Agent-Class為agent主類，Premain-Class類需定義public static void premain(String args, Instrumentation inst) 方法，Agent-Class類需定義public static void agentmain(String args, Instrumentation inst) 方法。
其他可選屬性為
- Can-Redefine-Classes 允許重定義類
- Can-Retransform-Classes 允許重轉換類
- Can-Set-Native-Method-Prefix 允許設置native method prefix
相关
- 核心接口及获取方式见 Instrumentation，JDK 内部实现见 InstrumentationImpl，底层依赖 JVMTI。
- 目前最常用的加载方式是运行时外部进程附加，不需要任何启动参数，详见 Instrumentation 的“运行时外部进程附加”一节。
Java's debug interface, commonly used for runtime class bytecode injection.
javaagent is a jar file with manifest attribute Premain-Class or Agent-Class, Premain-Class attribute and Agent-Class attribute declares the agent main class of a javaagent, the class speficied by Premain-Class should declare method public static void premain(String args, Instrumentation inst) , the class specified by Agent-Class should declare method public static void agentmain(String args, Instrumentation inst) .
Other optional attribute for a javaagent can be
- Can-Redefine-Classes
- Can-Retransform-Classes
- Can-Set-Native-Method-Prefix
Related
- See Instrumentation for provided methods and how to load a javaagent, see InstrumentationImpl for default implementation at runtime, see JVMTI for underlying mechanism.
- "runtime attach" is the most commonly used method to load a javaagent at present, it doesn't require any commandline arguments, see Instrumentation for more details.