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157 lines
4.1 KiB
Markdown
157 lines
4.1 KiB
Markdown
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> 反编译指定已加载类的源码
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`jad` 命令将 JVM 中实际运行的 class 的 byte code 反编译成 java 代码，便于你理解业务逻辑；
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* 在 Arthas Console 上，反编译出来的源码是带语法高亮的，阅读更方便
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* 当然，反编译出来的 java 代码可能会存在语法错误，但不影响你进行阅读理解
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### 参数说明
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|参数名称|参数说明|
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|---:|:---|
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|*class-pattern*|类名表达式匹配|
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|`[c:]`|类所属 ClassLoader 的 hashcode|
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|`[classLoaderClass:]`|指定执行表达式的 ClassLoader 的 class name|
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|[E]|开启正则表达式匹配，默认为通配符匹配|
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### 使用参考
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#### 编译`java.lang.String`
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`jad java.lang.String`{{execute T2}}
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```java
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$ jad java.lang.String
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ClassLoader:
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Location:
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/*
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* Decompiled with CFR 0_132.
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*/
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package java.lang;
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import java.io.ObjectStreamField;
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...
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public final class String
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implements Serializable,
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Comparable<String>,
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CharSequence {
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private final char[] value;
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private int hash;
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private static final long serialVersionUID = -6849794470754667710L;
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private static final ObjectStreamField[] serialPersistentFields = new ObjectStreamField[0];
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public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();
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public String(byte[] arrby, int n, int n2) {
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String.checkBounds(arrby, n, n2);
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this.value = StringCoding.decode(arrby, n, n2);
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}
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...
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```
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#### 反编译时只显示源代码
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默认情况下，反编译结果里会带有`ClassLoader`信息，通过`--source-only`选项，可以只打印源代码。方便和`mc`/`redefine`命令结合使用。
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`jad --source-only java.lang.String`{{execute T2}}
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```
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$ jad --source-only java.lang.String
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...
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@Override
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public int compare(String string, String string2) {
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int n = string.length();
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int n2 = string2.length();
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int n3 = Math.min(n, n2);
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for (int i = 0; i < n3; ++i) {
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char c;
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char c2 = string.charAt(i);
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if (c2 == (c = string2.charAt(i)) || (c2 = Character.toUpperCase(c2)) == (c = Character.toUpperCase(c)) || (c2 = Character.toLowerCase(c2)) == (c = Character.toLowerCase(c))) continue;
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return c2 - c;
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}
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return n - n2;
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}
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private Object readResolve() {
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return String.CASE_INSENSITIVE_ORDER;
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}
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}
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}
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```
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#### 反编译指定的函数
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`jad java.lang.String toString`{{execute T2}}
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```java
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$ jad java.lang.String toString
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ClassLoader:
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Location:
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@Override
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public String toString() {
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return this;
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}
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Affect(row-cnt:2) cost in 407 ms.
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```
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#### 反编译时指定ClassLoader
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> 当有多个 `ClassLoader` 都加载了这个类时，`jad` 命令会输出对应 `ClassLoader` 实例的 `hashcode`，然后你只需要重新执行 `jad` 命令，并使用参数 `-c <hashcode>` 就可以反编译指定 ClassLoader 加载的那个类了；
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例如：
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```java
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$ jad org.apache.log4j.Logger
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Found more than one class for: org.apache.log4j.Logger, Please use jad -c hashcode org.apache.log4j.Logger
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HASHCODE CLASSLOADER
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69dcaba4 +-monitor's ModuleClassLoader
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6e51ad67 +-java.net.URLClassLoader@6e51ad67
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+-sun.misc.Launcher$AppClassLoader@6951a712
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+-sun.misc.Launcher$ExtClassLoader@6fafc4c2
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2bdd9114 +-pandora-qos-service's ModuleClassLoader
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4c0df5f8 +-pandora-framework's ModuleClassLoader
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Affect(row-cnt:0) cost in 38 ms.
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```
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```java
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$ jad org.apache.log4j.Logger -c 69dcaba4
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ClassLoader:
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+-monitor's ModuleClassLoader
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Location:
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/Users/admin/app/log4j-1.2.14.jar
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package org.apache.log4j;
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import org.apache.log4j.spi.*;
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public class Logger extends Category
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{
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private static final String FQCN;
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protected Logger(String name)
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{
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super(name);
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}
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...
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Affect(row-cnt:1) cost in 190 ms.
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```
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对于只有唯一实例的ClassLoader还可以通过`--classLoaderClass`指定class name，使用起来更加方便：
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`--classLoaderClass` 的值是ClassLoader的类名，只有匹配到唯一的ClassLoader实例时才能工作，目的是方便输入通用命令，而`-c <hashcode>`是动态变化的。
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