(window.webpackJsonp=window.webpackJsonp||[]).push([[1586],{1994:function(t,a,s){"use strict";s.r(a);var n=s(31),e=Object(n.a)({},(function(){var t=this,a=t.$createElement,s=t._self._c||a;return s("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[s("h1",{attrs:{id:"java-agents"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#java-agents"}},[t._v("#")]),t._v(" Java Agents")]),t._v(" "),s("h2",{attrs:{id:"modifying-classes-with-agents"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#modifying-classes-with-agents"}},[t._v("#")]),t._v(" Modifying classes with agents")]),t._v(" "),s("p",[t._v("Firstly, make sure that the agent being used has the following attributes in the Manifest.mf:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Can")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Redefine")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Classes")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Can")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Retransform")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Classes")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),t._v("\n\n")])])]),s("p",[t._v("Starting a java agent will let the agent access the class Instrumentation. With Instrumentation you can call "),s("strong",[t._v("addTransformer(ClassFileTransformer transformer)")]),t._v(". ClassFileTransformers will let you rewrite the bytes of classes. The class has only a single method which supplies the ClassLoader that loads the class, the class's name, a java.lang.Class instance of it, it's ProtectionDomain, and lastly the bytes of the class itself.")]),t._v(" "),s("p",[t._v("It looks like this:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("byte")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("transform")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ClassLoader")]),t._v(" loader"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),t._v(" className"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Class")]),s("span",{pre:!0,attrs:{class:"token generics"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("?")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v(" classBeingRedefined"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" \n          "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ProtectionDomain")]),t._v(" protectionDomain"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("byte")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" classfileBuffer"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),s("p",[t._v("Modifying a class purely from bytes can take ages. 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