Frida基础用法详解：Java层操作指南<\/h1>

一、概述<\/h2>
本文档详细讲解Frida在Android逆向工程中Java层的七种基础用法，重点介绍如何通过Frida框架动态调用Java方法、Hook构造函数等技术。<\/p>

二、在现有实例上调用方法<\/h2>

1. 问题场景<\/h3>
当目标方法属于Activity类且未被直接调用时（如示例中的`flag<\/code>方法），直接创建实例会导致错误，因为Android组件需要特定上下文。<\/p>`

2. 解决方案<\/h3>
使用Java.choose()<\/code>枚举运行时已存在的实例：<\/p>
Java<\/span>.performNow<\/span>(function<\/span>() {
<\/span><\/span>    Java<\/span>.choose<\/span>('com.ad2001.frida0x5.MainActivity'<\/span>, {
<\/span><\/span>        onMatch<\/span>:<\/span> function<\/span>(instance<\/span>) {
<\/span><\/span>            console<\/span>.log<\/span>("Instance found"<\/span>);
<\/span><\/span>            instance<\/span>.flag<\/span>(1337<\/span>); \/\/ 调用目标方法
<\/span><\/span><\/span><\/span>        },
<\/span><\/span>        onComplete<\/span>:<\/span> function<\/span>() {}
<\/span><\/span>    });
<\/span><\/span>});
<\/span><\/span><\/code><\/pre>3. 关键点说明<\/h3>

Java.performNow<\/code>: 确保代码在Java运行时环境中执行<\/li>
Java.choose<\/code>: 枚举指定类的活动实例

第一个参数: 完整类名<\/li>
第二个参数: 包含onMatch<\/code>和onComplete<\/code>回调的对象<\/li>
<\/ul>
<\/li>
onMatch<\/code>: 对每个匹配实例执行的操作<\/li>
此方法适用于Activity等Android组件类<\/li>
<\/ul>
三、Hook构造函数<\/h2>
1. 问题场景<\/h3>
当需要修改对象初始化参数时（如示例中Checker<\/code>类的构造参数），可以通过Hook构造函数实现。<\/p>
2. 解决方案<\/h3>
Hook类的$init<\/code>方法（构造函数）：<\/p>
Java<\/span>.perform<\/span>(function<\/span>(){
<\/span><\/span>    var<\/span> a<\/span> =<\/span> Java<\/span>.use<\/span>("com.ad2001.frida0x7.Checker"<\/span>);
<\/span><\/span>    a<\/span>.$init<\/span>.implementation<\/span> =<\/span> function<\/span>(a<\/span>, b<\/span>){
<\/span><\/span>        console<\/span>.log<\/span>("Origin num:"<\/span>, a<\/span>, b<\/span>);
<\/span><\/span>        this<\/span>.$init<\/span>(1000<\/span>, 1000<\/span>); \/\/ 修改构造参数
<\/span><\/span><\/span><\/span>    }
<\/span><\/span>})
<\/span><\/span><\/code><\/pre>3. 关键点说明<\/h3>

Java.use<\/code>: 获取目标类的引用<\/li>
$init<\/code>: 表示类的构造函数<\/li>
implementation<\/code>: 重写方法实现<\/li>
可以在新实现中修改传入参数或完全改变构造行为<\/li>
<\/ul>
四、通用脚本模板<\/h2>
1. 对象参数调用方法模板<\/h3>
Java<\/span>.performNow<\/span>(function<\/span>() {
<\/span><\/span>    Java<\/span>.choose<\/span>('<Package>.<class_Name>'<\/span>, {
<\/span><\/span>        onMatch<\/span>:<\/span> function<\/span>(instance<\/span>) {
<\/span><\/span>            var<\/span> <<\/span>class_reference<\/span>><\/span> =<\/span> Java<\/span>.use<\/span>("<package_name>.<class>"<\/span>);
<\/span><\/span>            var<\/span> <<\/span>class_instance<\/span>><\/span> =<\/span> <<\/span>class_reference<\/span>><\/span>.$new<\/span>();
<\/span><\/span>            \/* 设置实例参数 *\/<\/span>
<\/span><\/span>            instance<\/span>.<<\/span>method<\/span>><\/span>(class_instance<\/span>);
<\/span><\/span>        },
<\/span><\/span>        onComplete<\/span>:<\/span> function<\/span>() {}
<\/span><\/span>    });
<\/span><\/span>});
<\/span><\/span><\/code><\/pre>2. Hook构造函数模板<\/h3>
Java<\/span>.perform<\/span>(function<\/span>() {
<\/span><\/span>    var<\/span> <<\/span>class_reference<\/span>><\/span> =<\/span> Java<\/span>.use<\/span>("<package_name>.<class>"<\/span>);
<\/span><\/span>    <<\/span>class_reference<\/span>><\/span>.$init<\/span>.implementation<\/span> =<\/span> function<\/span>(<<\/span>args<\/span>><\/span>){
<\/span><\/span>        \/* 自定义实现 *\/<\/span>
<\/span><\/span>    }
<\/span><\/span>});
<\/span><\/span><\/code><\/pre>五、注意事项<\/h2>

Android组件（如Activity）不能直接实例化，必须通过Java.choose<\/code>获取现有实例<\/li>
涉及UI操作必须在主线程执行<\/li>
构造函数Hook通过$init<\/code>实现<\/li>
使用console.log<\/code>输出调试信息<\/li>
确保脚本在目标应用启动后执行<\/li>
<\/ol>
六、总结<\/h2>
本文介绍了Frida在Java层的两种核心用法：<\/p>

通过Java.choose<\/code>获取现有实例并调用方法<\/li>
通过Hook$init<\/code>修改构造函数行为<\/li>
<\/ol>
这些技术可以绕过常规逻辑检查、修改运行时行为，是Android逆向工程的基础技能。后续将介绍Native层的进阶用法。<\/p>

Frida基础用法详解：Java层操作指南<\/h1>

一、概述<\/h2> 本文档详细讲解Frida在Android逆向工程中Java层的七种基础用法，重点介绍如何通过Frida框架动态调用Java方法、Hook构造函数等技术。<\/p>

二、在现有实例上调用方法<\/h2>

1. 问题场景<\/h3> 当目标方法属于Activity类且未被直接调用时（如示例中的flag<\/code>方法），直接创建实例会导致错误，因为Android组件需要特定上下文。<\/p>

三、Hook构造函数<\/h2>

1. 问题场景<\/h3> 当需要修改对象初始化参数时（如示例中Checker<\/code>类的构造参数），可以通过Hook构造函数实现。<\/p>

四、通用脚本模板<\/h2>

一、概述<\/h2>
本文档详细讲解Frida在Android逆向工程中Java层的七种基础用法，重点介绍如何通过Frida框架动态调用Java方法、Hook构造函数等技术。<\/p>

1. 问题场景<\/h3>
当目标方法属于Activity类且未被直接调用时（如示例中的`flag<\/code>方法），直接创建实例会导致错误，因为Android组件需要特定上下文。<\/p>`

1. 问题场景<\/h3>
当需要修改对象初始化参数时（如示例中`Checker<\/code>类的构造参数），可以通过Hook构造函数实现。<\/p>`