arthas/tutorials/katacoda/command-jad-en/jad.md

> Decompile the specified classes.

`jad` helps to decompile the byte code running in JVM to the source code to assist you to understand the logic behind better.

* The decompiled code is syntax highlighted for better readability in Arthas console.
* It is possible that there's grammar error in the decompiled code, but it should not affect your interpretation.

### Options

|Name|Specification|
|---:|:---|
|*class-pattern*|pattern for the class name|
|`[c:]`|hashcode of the class loader that loads the class|
|`[classLoaderClass:]`| The class name of the ClassLoader that executes the expression. |
|`[E]`|turn on regex match while the default is wildcard match|

### Usage

#### Decompile `java.lang.String`

`jad java.lang.String`{{execute T2}}

```java
$ jad java.lang.String

ClassLoader:

Location:


/*
* Decompiled with CFR 0_132.
*/
package java.lang;

import java.io.ObjectStreamField;
...
public final class String
implements Serializable,
Comparable<String>,
CharSequence {
    private final char[] value;
    private int hash;
    private static final long serialVersionUID = -6849794470754667710L;
    private static final ObjectStreamField[] serialPersistentFields = new ObjectStreamField[0];
    public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();

    public String(byte[] arrby, int n, int n2) {
        String.checkBounds(arrby, n, n2);
        this.value = StringCoding.decode(arrby, n, n2);
    }
...
```

#### Print source only

By default, the decompile result will have the `ClassLoader` information. With the `--source-only` option, you can print only the source code. Conveniently used with the [mc](mc.md)/[redefine](redefine.md) commands.

`jad --source-only java.lang.String`{{execute T2}}

```
$ jad --source-only java.lang.String
...
        @Override
        public int compare(String string, String string2) {
            int n = string.length();
            int n2 = string2.length();
            int n3 = Math.min(n, n2);
            for (int i = 0; i < n3; ++i) {
                char c;
                char c2 = string.charAt(i);
                if (c2 == (c = string2.charAt(i)) || (c2 = Character.toUpperCase(c2)) == (c = Character.toUpperCase(c)) || (c2 = Character.toLowerCase(c2)) == (c = Character.toLowerCase(c))) continue;
                return c2 - c;
            }
            return n - n2;
        }

        private Object readResolve() {
            return String.CASE_INSENSITIVE_ORDER;
        }
    }
}
```

#### Decompile the specified method

`jad java.lang.String toString`{{execute T2}}

```java
$ jad java.lang.String toString

ClassLoader:

Location:


@Override
public String toString() {
    return this;
}

Affect(row-cnt:2) cost in 407 ms.
```

#### Decompile with specified classLoader

> If the target class is loaded by multiple classloaders, `jad` outputs the `hashcode` of the corresponding classloaders, then you can re-run `jad` and specify `-c <hashcode>` to decompile the target class from the specified classloader.

Examples:

```java
$ jad org.apache.log4j.Logger

Found more than one class for: org.apache.log4j.Logger, Please use jad -c hashcode org.apache.log4j.Logger
HASHCODE  CLASSLOADER
69dcaba4  +-monitor's ModuleClassLoader
6e51ad67  +-java.net.URLClassLoader@6e51ad67
            +-sun.misc.Launcher$AppClassLoader@6951a712
            +-sun.misc.Launcher$ExtClassLoader@6fafc4c2
2bdd9114  +-pandora-qos-service's ModuleClassLoader
4c0df5f8  +-pandora-framework's ModuleClassLoader

Affect(row-cnt:0) cost in 38 ms.
```

```java
$ jad org.apache.log4j.Logger -c 69dcaba4

ClassLoader:
+-monitor's ModuleClassLoader

Location:
/Users/admin/app/log4j-1.2.14.jar

package org.apache.log4j;

import org.apache.log4j.spi.*;

public class Logger extends Category
{
    private static final String FQCN;

    protected Logger(String name)
    {
        super(name);
    }

...

Affect(row-cnt:1) cost in 190 ms.
```

For classloader with only one instance, it can be specified by `--classLoaderClass` using class name, which is more convenient to use.

The value of `--classloaderclass` is the class name of classloader. It can only work when it matches a unique classloader instance. The purpose is to facilitate the input of general commands. However, `-c <hashcode>` is dynamic.