android 运行时生成dex文件，并装载调用

android apk生成原理如下图所示

从图可看出是把java文件通过java编译工具编译成class文件，再通过dex工具把class文件转成dex文件

因为好奇，从网上看到运行时生成class文件，再转成dex文件，动态加载调用的写法，和大家分享。

package org.jamruby.javassistsample;import java.io.File;import java.lang.reflect.Constructor;import java.lang.reflect.Method;import dalvik.system.DexClassLoader;import javassist.ClassPool;import javassist.CtClass;import javassist.CtConstructor;import javassist.CtMethod;import javassist.android.DexFile;import android.os.Bundle;import android.os.Handler;import android.app.Activity;import android.view.Menu;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends Activity {    private static final String DEX_FILE_NAME_MYCLASSES = "myclasses.dex";    private static final boolean FORCE_GENRATE_DEX = false;@Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                final TextView view = (TextView)findViewById(R.id.textview_title);        final File dexFile = new File(getFilesDir(), DEX_FILE_NAME_MYCLASSES);                if (!dexFile.exists() || FORCE_GENRATE_DEX) {        // generate DEX and ODEX file.        try {        // generate "xxx.class" file via Javassist.        final ClassPool cp = ClassPool.getDefault(getApplicationContext());        final CtClass cls = cp.makeClass("hoge");        final CtConstructor ctor = new CtConstructor(null, cls);        ctor.setBody("{}");        cls.addConstructor(ctor);final CtMethod m1 = CtMethod.make("public java.lang.String toString() { return \"hoge.toString() is called.\"; }",cls);cls.addMethod(m1);final CtMethod m2 = CtMethod.make("public void setText(android.widget.TextView view) { view.setText((java.lang.CharSequence)\"hoge.setText() is called.\"); }",cls);cls.addMethod(m2);cls.writeFile(getFilesDir().getAbsolutePath());// convert from "xxx.class" to "xxx.dex"        final DexFile df = new DexFile();        final String dexFilePath = dexFile.getAbsolutePath();        df.addClass(new File(getFilesDir(), "hoge.class"));        df.writeFile(dexFilePath);        } catch (Exception e) {        e.printStackTrace();        Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();        }        }                if (dexFile.exists()) {        try {        final DexClassLoader dcl = new DexClassLoader(        dexFile.getAbsolutePath(),        getCacheDir().getAbsolutePath(),        getApplicationInfo().nativeLibraryDir,        getClassLoader());        String title = null;        final Class<?> class_hoge = dcl.loadClass("hoge");final Constructor<?> ctor = class_hoge.getConstructor(new Class<?>[0]);final Object obj = ctor.newInstance(new Object[0]);title = obj.toString();view.setText(title);new Handler().postDelayed(new Runnable() {@Overridepublic void run() {try {final Method m = obj.getClass().getDeclaredMethod("setText", TextView.class);m.invoke(obj, view);} catch (Exception e) {e.printStackTrace();Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();}}}, 2000);        } catch (Exception e) {        e.printStackTrace();        Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();        }        }    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        getMenuInflater().inflate(R.menu.activity_main, menu);        return true;    }}

源代码从附件中下载，导入三个工程

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