原文地址：http://www.infoq.com/cn/articles/javaagent-illustrated
文章里也会讲到JVMTIAgent(C实现的)，因为javaagent的运行还是依赖于一个特殊的JVMTIAgent。
用法大致如下：
java -javaagent:myagent.jar=mode=test Test功能如下：
- 文件之前做拦截，对字节码做修改
- 功能
- 获取所有已经加载过的类
- 获取所有已经初始化过的类（执行过clinit方法，是上面的一个子集）
- 获取某个对象的大小
- 方法的前缀，主要在查找native方法的时候做规则匹配
jvmtiEnv <span class="token operator">* jvmtienv <span class="token operator">= <span class="token function">jvmti<span class="token punctuation">(agent<span class="token punctuation">)<span class="token punctuation">;
jvmtiError jvmtierror<span class="token punctuation">;
<span class="token function">memset<span class="token punctuation">(<span class="token operator">&callbacks<span class="token punctuation">,<span class="token number">0<span class="token punctuation">,<span class="token keyword">sizeof<span class="token punctuation">(callbacks<span class="token punctuation">)<span class="token punctuation">)<span class="token punctuation">;
callbacks<span class="token punctuation">.ClassFileLoadHook <span class="token operator">= <span class="token operator">&eventHandlerClassFileLoadHook<span class="token punctuation">;
jvmtierror <span class="token operator">= <span class="token punctuation">(<span class="token operator">*jvmtienv<span class="token punctuation">)<span class="token operator">-<span class="token operator">><span class="token function">SetEventCallbacks<span class="token punctuation">( jvmtienv<span class="token punctuation">,<span class="token operator">&callbacks<span class="token punctuation">,<span class="token keyword">sizeof<span class="token punctuation">(callbacks<span class="token punctuation">)<span class="token punctuation">)<span class="token punctuation">;</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code></pre><h1 class="p1"><span class="s1">JVMTIAgent
<p class="p2"><span class="s1">JVMTIAgent其实就是一个动态库，利用JVMTI暴露出来的一些接口来干一些我们想做、但是正常情况下又做不到的事情，不过为了和普通的动态库进行区分，它一般会实现如下的一个或者多个函数：
<pre class=" language-cpp"><code class=" language-cpp">JNIEXPORT jint JNICALL
<span class="token function">Agent_OnLoad<span class="token punctuation">(JavaVM <span class="token operator">vm<span class="token punctuation">,<span class="token keyword">char <span class="token operator">options<span class="token punctuation">,<span class="token keyword">void <span class="token operator">*reserved<span class="token punctuation">)<span class="token punctuation">;
JNIEXPORT jint JNICALL
<span class="token function">Agent_OnAttach<span class="token punctuation">(JavaVM<span class="token operator"> vm<span class="token punctuation">,<span class="token keyword">char<span class="token operator"> options<span class="token punctuation">,<span class="token keyword">void<span class="token operator">* reserved<span class="token punctuation">)<span class="token punctuation">;
JNIEXPORT <span class="token keyword">void JNICALL
<span class="token function">Agent_OnUnload<span class="token punctuation">(JavaVM <span class="token operator">*vm<span class="token punctuation">)<span class="token punctuation">;
<ul class="ul1">
<li class="li2"><span class="s4">Agent_OnLoad<span class="s1">函数，如果agent是在启动时加载的，也就是在vm参数里通过-agentlib来指定的，那在启动过程中就会去执行这个agent里的<span class="s4">Agent_OnLoad<span class="s1">函数。
<li class="li2"><span class="s4">Agent_OnAttach<span class="s1">函数，如果agent不是在启动时加载的，而是我们先attach到目标进程上，然后给对应的目标进程发送load命令来加载，则在加载过程中会调用<span class="s4">Agent_OnAttach<span class="s1">函数。
<li class="li2"><span class="s4">Agent_OnUnload<span class="s1">函数，在agent卸载时调用，不过貌似基本上很少实现它。
struct _JPLISEnvironment <span class="token punctuation">{
jvmtiEnv <span class="token operator"> mJVMTIEnv<span class="token punctuation">; <span class="token comment">/ the JVM TI environment /
JPLISAgent <span class="token operator"> mAgent<span class="token punctuation">; <span class="token comment">/ corresponding agent /
jboolean mIsRetransformer<span class="token punctuation">; <span class="token comment">/ indicates if special environment /
<span class="token punctuation">}<span class="token punctuation">;<p class="p2"><span class="s1">这里解释一下几个重要项：
- 功能。
- 功能。
- 方法的时候注意到了有个Instrumentation参数，该参数其实就是这里的对象。
- 方法，如果agent是在启动时加载的，则该方法会被调用。
- 方法，该方法在通过attach的方式动态加载agent的时候调用。
- 方法。
- 功能，在javaagent的MANIFEST.MF里设置`Can-Redefine-Classes:true`。
- 支持native方法前缀设置，同样在javaagent的MANIFEST.MF里设置`Can-Set-Native-Method-Prefix:true`。
- 文件里定义了`Can-Retransform-Classes:true`，将会设置mRetransformEnvironment的mIsRetransformer为true。
方法里，这里简单描述下过程：
- 内容
文件之后回调时用的，这样可以对原来的字节码做修改，那这里面究竟是怎样实现的呢？
<span class="token function">eventHandlerClassFileLoadHook<span class="token punctuation">( jvmtiEnv <span class="token operator"> jvmtienv<span class="token punctuation">,JNIEnv <span class="token operator"> jnienv<span class="token punctuation">,jclass <span class="token class-name">class_being_redefined<span class="token punctuation">,jobject loader<span class="token punctuation">,<span class="token keyword">const <span class="token keyword">char<span class="token operator"> name<span class="token punctuation">,jobject protectionDomain<span class="token punctuation">,jint class_data_len<span class="token punctuation">,<span class="token keyword">const <span class="token keyword">unsigned <span class="token keyword">char<span class="token operator"> class_data<span class="token punctuation">,jint<span class="token operator"> new_class_data_len<span class="token punctuation">,<span class="token keyword">unsigned <span class="token keyword">char<span class="token operator"><span class="token operator">* new_class_data<span class="token punctuation">) <span class="token punctuation">{
JPLISEnvironment <span class="token operator">* environment <span class="token operator">= <span class="token constant">NULL<span class="token punctuation">;
environment <span class="token operator">= <span class="token function">getJPLISEnvironment<span class="token punctuation">(jvmtienv<span class="token punctuation">)<span class="token punctuation">;
<span class="token comment">/* if something is internally inconsistent (no agent),just silently return without touching the buffer */
<span class="token keyword">if <span class="token punctuation">( environment <span class="token operator">!= <span class="token constant">NULL <span class="token punctuation">) <span class="token punctuation">{
jthrowable outstandingException <span class="token operator">= <span class="token function">preserveThrowable<span class="token punctuation">(jnienv<span class="token punctuation">)<span class="token punctuation">;
<span class="token function">transformClassFile<span class="token punctuation">( environment<span class="token operator">-<span class="token operator">>mAgent<span class="token punctuation">,jnienv<span class="token punctuation">,loader<span class="token punctuation">,name<span class="token punctuation">,class_being_redefined<span class="token punctuation">,protectionDomain<span class="token punctuation">,class_data_len<span class="token punctuation">,class_data<span class="token punctuation">,new_class_data_len<span class="token punctuation">,new_class_data<span class="token punctuation">,environment<span class="token operator">-<span class="token operator">>mIsRetransformer<span class="token punctuation">)<span class="token punctuation">;
<span class="token function">restoreThrowable<span class="token punctuation">(jnienv<span class="token punctuation">,outstandingException<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token punctuation">}
<p class="p2"><span class="s1">先根据jvmtiEnv取得对应的JPLISEnvironment，因为上面我已经说到其实有两个JPLISEnvironment（并且有两个jvmtiEnv），其中一个是专门做retransform的，而另外一个用来做其他事情，根据不同的用途，在注册具体的ClassFileTransformer时也是分开的，对于作为retransform用的ClassFileTransformer，我们会注册到一个单独的TransformerManager里。
<p class="p2"><span class="s1">接着调用transformClassFile方法，由于函数实现比较长，这里就不贴代码了，大致意思就是调用InstrumentationImpl对象的transform方法，根据最后那个参数来决定选哪个TransformerManager里的ClassFileTransformer对象们做transform操作。
<pre class=" language-java"><code class=" language-java"><span class="token keyword">private <span class="token keyword">byte<span class="token punctuation">[<span class="token punctuation">]
<span class="token function">transform<span class="token punctuation">( ClassLoader loader<span class="token punctuation">,String classname<span class="token punctuation">,Class <span class="token class-name">classBeingRedefined<span class="token punctuation">,ProtectionDomain protectionDomain<span class="token punctuation">,<span class="token keyword">byte<span class="token punctuation">[<span class="token punctuation">] classfileBuffer<span class="token punctuation">,<span class="token keyword">boolean isRetransformer<span class="token punctuation">) <span class="token punctuation">{
TransformerManager mgr <span class="token operator">= isRetransformer<span class="token operator">?
mRetransfomableTransformerManager <span class="token operator">:
mTransformerManager<span class="token punctuation">;
<span class="token keyword">if <span class="token punctuation">(mgr <span class="token operator">== null<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">return null<span class="token punctuation">; <span class="token comment">// no manager,no transform
<span class="token punctuation">} <span class="token keyword">else <span class="token punctuation">{
<span class="token keyword">return mgr<span class="token punctuation">.<span class="token function">transform<span class="token punctuation">( loader<span class="token punctuation">,classname<span class="token punctuation">,classBeingRedefined<span class="token punctuation">,classfileBuffer<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token punctuation">}<span class="token keyword">public <span class="token keyword">byte<span class="token punctuation">[<span class="token punctuation">]
<span class="token function">transform<span class="token punctuation">( ClassLoader loader<span class="token punctuation">,<span class="token keyword">byte<span class="token punctuation">[<span class="token punctuation">] classfileBuffer<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">boolean someoneTouchedTheBytecode <span class="token operator">= <span class="token boolean">false<span class="token punctuation">;
TransformerInfo<span class="token punctuation">[<span class="token punctuation">] transformerList <span class="token operator">= <span class="token function">getSnapshotTransformerList<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">;
<span class="token keyword">byte<span class="token punctuation">[<span class="token punctuation">] bufferToUse <span class="token operator">= classfileBuffer<span class="token punctuation">;
<span class="token comment">// order matters,gotta run 'em in the order they were added
<span class="token keyword">for <span class="token punctuation">( <span class="token keyword">int x <span class="token operator">= <span class="token number">0<span class="token punctuation">; x <span class="token operator">< transformerList<span class="token punctuation">.length<span class="token punctuation">; x<span class="token operator">++ <span class="token punctuation">) <span class="token punctuation">{
TransformerInfo transformerInfo <span class="token operator">= transformerList<span class="token punctuation">[x<span class="token punctuation">]<span class="token punctuation">;
ClassFileTransformer transformer <span class="token operator">= transformerInfo<span class="token punctuation">.<span class="token function">transformer<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">;
<span class="token keyword">byte<span class="token punctuation">[<span class="token punctuation">] transformedBytes <span class="token operator">= null<span class="token punctuation">;
<span class="token keyword">try <span class="token punctuation">{
transformedBytes <span class="token operator">= transformer<span class="token punctuation">.<span class="token function">transform<span class="token punctuation">( loader<span class="token punctuation">,bufferToUse<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token keyword">catch <span class="token punctuation">(<span class="token class-name">Throwable t<span class="token punctuation">) <span class="token punctuation">{
<span class="token comment">// don't let any one transformer mess it up for the others.
<span class="token comment">// This is where we need to put some logging. What should go here? FIXME
<span class="token punctuation">}
<span class="token keyword">if <span class="token punctuation">( transformedBytes <span class="token operator">!= null <span class="token punctuation">) <span class="token punctuation">{
someoneTouchedTheBytecode <span class="token operator">= <span class="token boolean">true<span class="token punctuation">;
bufferToUse <span class="token operator">= transformedBytes<span class="token punctuation">;
<span class="token punctuation">}
<span class="token punctuation">}
<span class="token comment">// if someone modified it,return the modified buffer.
<span class="token comment">// otherwise return null to mean "no transforms occurred"
<span class="token keyword">byte <span class="token punctuation">[<span class="token punctuation">] result<span class="token punctuation">;
<span class="token keyword">if <span class="token punctuation">( someoneTouchedTheBytecode <span class="token punctuation">) <span class="token punctuation">{
result <span class="token operator">= bufferToUse<span class="token punctuation">;
<span class="token punctuation">}
<span class="token keyword">else <span class="token punctuation">{
result <span class="token operator">= null<span class="token punctuation">;
<span class="token punctuation">}
<span class="token keyword">return result<span class="token punctuation">;
<span class="token punctuation">}
<p class="p3">以上是最终调到的java代码，可以看到已经调用到我们自己编写的javaagent代码里了，我们一般是实现一个ClassFileTransformer类，然后创建一个对象注册到对应的TransformerManager里。
<h1 class="p1"><span class="s1">Class Transform的实现
<p class="p2"><span class="s1">这里说的class transform其实是狭义的，主要是针对第一次类文件加载时就要求被transform的场景，在加载类文件的时候发出ClassFileLoad事件，然后交给instrumenat agent来调用javaagent里注册的ClassFileTransformer实现字节码的修改。
<h1 class="p1"><span class="s1">Class Redefine的实现
<p class="p2"><span class="s1">类重新定义，这是Instrumentation提供的基础功能之一，主要用在已经被加载过的类上，想对其进行修改，要做这件事，我们必须要知道两个东西，一个是要修改哪个类，另外一个是想将那个类修改成怎样的结构，有了这两个信息之后就可以通过InstrumentationImpl下面的redefineClasses方法操作了：
<pre class=" language-java"><code class=" language-java"><span class="token keyword">public <span class="token keyword">void <span class="token function">redefineClasses<span class="token punctuation">(ClassDefinition<span class="token punctuation">[<span class="token punctuation">] definitions<span class="token punctuation">) <span class="token keyword">throws ClassNotFoundException <span class="token punctuation">{
<span class="token keyword">if <span class="token punctuation">(<span class="token operator">!<span class="token function">isRedefineClassesSupported<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">throw <span class="token keyword">new <span class="token class-name">UnsupportedOperationException<span class="token punctuation">(<span class="token string">"redefineClasses is not supported in this environment"<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token keyword">if <span class="token punctuation">(definitions <span class="token operator">== null<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">throw <span class="token keyword">new <span class="token class-name">NullPointerException<span class="token punctuation">(<span class="token string">"null passed as 'definitions' in redefineClasses"<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token keyword">for <span class="token punctuation">(<span class="token keyword">int i <span class="token operator">= <span class="token number">0<span class="token punctuation">; i <span class="token operator">< definitions<span class="token punctuation">.length<span class="token punctuation">; <span class="token operator">++i<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">if <span class="token punctuation">(definitions<span class="token punctuation">[i<span class="token punctuation">] <span class="token operator">== null<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">throw <span class="token keyword">new <span class="token class-name">NullPointerException<span class="token punctuation">(<span class="token string">"element of 'definitions' is null in redefineClasses"<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token punctuation">}
<span class="token keyword">if <span class="token punctuation">(definitions<span class="token punctuation">.length <span class="token operator">== <span class="token number">0<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">return<span class="token punctuation">; <span class="token comment">// short-circuit if there are no changes requested
<span class="token punctuation">}
<span class="token function">redefineClasses0<span class="token punctuation">(mNativeAgent<span class="token punctuation">,definitions<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<p class="p3"><span class="s1">在JVM里对应的实现是创建一个<span class="s4">VM_RedefineClasses<span class="s1">的<span class="s4">VM_Operation<span class="s1">，注意执行它的时候会stop-the-world：
<pre class=" language-cpp"><code class=" language-cpp">jvmtiError
JvmtiEnv<span class="token operator">::<span class="token function">RedefineClasses<span class="token punctuation">(jint class_count<span class="token punctuation">,<span class="token keyword">const jvmtiClassDefinition<span class="token operator">* class_definitions<span class="token punctuation">) <span class="token punctuation">{
<span class="token comment">//TODO: add locking
VM_RedefineClasses <span class="token function">op<span class="token punctuation">(class_count<span class="token punctuation">,class_definitions<span class="token punctuation">,jvmti_class_load_kind_redefine<span class="token punctuation">)<span class="token punctuation">;
VMThread<span class="token operator">::<span class="token function">execute<span class="token punctuation">(<span class="token operator">&op<span class="token punctuation">)<span class="token punctuation">;
<span class="token keyword">return <span class="token punctuation">(op<span class="token punctuation">.<span class="token function">check_error<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">} <span class="token comment">/ end RedefineClasses /
<p class="p2"><span class="s1">这个过程我尽量用语言来描述清楚，不详细贴代码了，因为代码量实在有点大：
<ul class="ul1">
<li class="li2"><span class="s1">挨个遍历要批量重定义的jvmtiClassDefinition
<li class="li2"><span class="s1">然后读取新的字节码，如果有关注ClassFileLoadHook事件的，还会走对应的transform来对新的字节码再做修改
<li class="li2"><span class="s1">字节码解析好，创建一个klassOop对象
<li class="li2">
<span class="s1"><span class="s1">对比新老类，并要求如下：
<ul class="ul2">
<li class="li2"><span class="s1">父类是同一个
<li class="li2"><span class="s1">实现的接口数也要相同，并且是相同的接口
<li class="li2"><span class="s1">类访问符必须一致
<li class="li2"><span class="s1">字段数和字段名要一致
<li class="li2"><span class="s1">新增的方法必须是private static/final的
<li class="li2"><span class="s1">可以删除修改方法
内容，相当于只更新了指针指向的内容，并没有更新指针，避免了遍历大量已有类对象对它们进行更新所带来的开销。
方法参数看猜到应该是做回滚操作，因为我们只指定了class：
<span class="token keyword">if <span class="token punctuation">(<span class="token operator">!<span class="token function">isRetransformClassesSupported<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">throw <span class="token keyword">new <span class="token class-name">UnsupportedOperationException<span class="token punctuation">( <span class="token string">"retransformClasses is not supported in this environment"<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token function">retransformClasses0<span class="token punctuation">(mNativeAgent<span class="token punctuation">,classes<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code></pre><p class="p2"><span class="s1">不过retransform的实现其实也是通过redefine的功能来实现，在类加载的时候有比较小的差别，主要体现在究竟会走哪些transform上，如果当前是做retransform的话，那将忽略那些注册到正常的TransformerManager里的ClassFileTransformer，而只会走专门为retransform而准备的TransformerManager的ClassFileTransformer，不然想象一下字节码又被无声无息改成某个中间态了。
<pre class=" language-java"><code class=" language-java"><span class="token keyword">private<span class="token operator">:
<span class="token keyword">void <span class="token function">post_all_envs<span class="token punctuation">(<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">if <span class="token punctuation">(_load_kind <span class="token operator">!= jvmti_class_load_kind_retransform<span class="token punctuation">) <span class="token punctuation">{
<span class="token comment">// for class load and redefine,<span class="token comment">// call the non-retransformable agents
JvmtiEnvIterator it<span class="token punctuation">;
<span class="token keyword">for <span class="token punctuation">(JvmtiEnv<span class="token operator">* env <span class="token operator">= it<span class="token punctuation">.<span class="token function">first<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">; env <span class="token operator">!= NULL<span class="token punctuation">; env <span class="token operator">= it<span class="token punctuation">.<span class="token function">next<span class="token punctuation">(env<span class="token punctuation">)<span class="token punctuation">) <span class="token punctuation">{
<span class="token keyword">if <span class="token punctuation">(<span class="token operator">!env<span class="token operator">-<span class="token operator">><span class="token function">is_retransformable<span class="token punctuation">(<span class="token punctuation">) <span class="token operator">&& env<span class="token operator">-<span class="token operator">><span class="token function">is_enabled<span class="token punctuation">(JVMTI_EVENT_CLASS_FILE_LOAD_HOOK<span class="token punctuation">)<span class="token punctuation">) <span class="token punctuation">{
<span class="token comment">// non-retransformable agents cannot retransform back,<span class="token comment">// so no need to cache the original class file bytes
<span class="token function">post_to_env<span class="token punctuation">(env<span class="token punctuation">,<span class="token boolean">false<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token punctuation">}
<span class="token punctuation">}
JvmtiEnvIterator it<span class="token punctuation">;
<span class="token keyword">for <span class="token punctuation">(JvmtiEnv<span class="token operator">* env <span class="token operator">= it<span class="token punctuation">.<span class="token function">first<span class="token punctuation">(<span class="token punctuation">)<span class="token punctuation">; env <span class="token operator">!= NULL<span class="token punctuation">; env <span class="token operator">= it<span class="token punctuation">.<span class="token function">next<span class="token punctuation">(env<span class="token punctuation">)<span class="token punctuation">) <span class="token punctuation">{
<span class="token comment">// retransformable agents get all events
<span class="token keyword">if <span class="token punctuation">(env<span class="token operator">-<span class="token operator">><span class="token function">is_retransformable<span class="token punctuation">(<span class="token punctuation">) <span class="token operator">&& env<span class="token operator">-<span class="token operator">><span class="token function">is_enabled<span class="token punctuation">(JVMTI_EVENT_CLASS_FILE_LOAD_HOOK<span class="token punctuation">)<span class="token punctuation">) <span class="token punctuation">{
<span class="token comment">// retransformable agents need to cache the original class file
<span class="token comment">// bytes if changes are made via the ClassFileLoadHook
<span class="token function">post_to_env<span class="token punctuation">(env<span class="token punctuation">,<span class="token boolean">true<span class="token punctuation">)<span class="token punctuation">;
<span class="token punctuation">}
<span class="token punctuation">}<span class="token punctuation">}
<h1 class="p3">javaagent的其他小众功能
<p class="p2"><span class="s1">javaagent除了做字节码上面的修改之外，其实还有一些小功能，有时候还是挺有用的
<ul class="ul1">
<li class="li6"><span class="s7">获取所有已经被加载的类：<span class="s8">Class[] getAllLoadedClasses();
<li class="li6"><span class="s7">获取所有已经初始化了的类： <span class="s8">Class[] getInitiatedClasses(ClassLoader loader);
<li class="li6"><span class="s7">获取某个对象的大小： <span class="s8">long getObjectSize(Object objectToSize);
<li class="li6"><span class="s7">将某个jar加入到bootstrap classpath里优先其他jar被加载： <span class="s8">void appendToBootstrapClassLoaderSearch(JarFile jarfile);
<li class="li6"><span class="s7">将某个jar加入到classpath里供appclassloard去加载：<span class="s8">void appendToSystemClassLoaderSearch(JarFile jarfile);
<li class="li6"><span class="s7">设置某些native方法的前缀，主要在找native方法的时候做规则匹配： <span class="s8">void setNativeMethodPrefix(ClassFileTransformer transformer,String prefix)。 原文链接：https://www.f2er.com/jvm/72280.html
