動態類生成預加載-dexmaker使用

下面這個例子非常典型，可以說入門非常好了。過程很簡單，生成一個包含一個函數的類，在主程序裏面動態加載（使用ClassLoader），然後執行類裏面的函數。這裏雖然是寫在main函數裏的，但是你完全可以將這mian裏邊的代碼放到acticty中實現。注意：進過樓主的實驗，放到Android的junit下跑會報錯的。注意添加文件權限。

public final class HelloWorldMaker {
    public static void main(String[] args) throws Exception {
        DexMaker dexMaker = new DexMaker();

        // Generate a HelloWorld class.
        TypeId<?> helloWorld = TypeId.get("LHelloWorld;");
        dexMaker.declare(helloWorld, "HelloWorld.generated", Modifier.PUBLIC, TypeId.OBJECT);
        generateHelloMethod(dexMaker, helloWorld);

        // Create the dex file and load it.
                //File outputDir = getApplicationContext().getDir("dx", Context.MODE_PRIVATE);
                //建議在android上測試時使用這個文件路徑
        File outputDir = new File(".");
        ClassLoader loader = dexMaker.generateAndLoad(HelloWorldMaker.class.getClassLoader(),
                outputDir, outputDir);
        Class<?> helloWorldClass = loader.loadClass("HelloWorld");

        // Execute our newly-generated code in-process.
        helloWorldClass.getMethod("hello").invoke(null);
    }

    private static void generateHelloMethod(DexMaker dexMaker, TypeId<?> declaringType) {
        // Lookup some types we‘ll need along the way.
        TypeId<System> systemType = TypeId.get(System.class);
        TypeId<PrintStream> printStreamType = TypeId.get(PrintStream.class);

        // Identify the ‘hello()‘ method on declaringType.
        MethodId hello = declaringType.getMethod(TypeId.VOID, "hello");

        // Declare that method on the dexMaker. Use the returned Code instance
        // as a builder that we can append instructions to.
        Code code = dexMaker.declare(hello, Modifier.STATIC | Modifier.PUBLIC);

        // Declare all the locals we‘ll need up front. The API requires this.
        Local<Integer> a = code.newLocal(TypeId.INT);
        Local<Integer> b = code.newLocal(TypeId.INT);
        Local<Integer> c = code.newLocal(TypeId.INT);
        Local<String> s = code.newLocal(TypeId.STRING);
        Local<PrintStream> localSystemOut = code.newLocal(printStreamType);

        // int a = 0xabcd;
        code.loadConstant(a, 0xabcd);

        // int b = 0xaaaa;
        code.loadConstant(b, 0xaaaa);

        // int c = a - b;
        code.op(BinaryOp.SUBTRACT, c, a, b);

        // String s = Integer.toHexString(c);
        MethodId<Integer, String> toHexString
                = TypeId.get(Integer.class).getMethod(TypeId.STRING, "toHexString", TypeId.INT);
        code.invokeStatic(toHexString, s, c);

        // System.out.println(s);
        FieldId<System, PrintStream> systemOutField = systemType.getField(printStreamType, "out");
        code.sget(systemOutField, localSystemOut);
        MethodId<PrintStream, Void> printlnMethod = printStreamType.getMethod(
                TypeId.VOID, "println", TypeId.STRING);
        code.invokeVirtual(printlnMethod, null, localSystemOut, s);

        // return;
        code.returnVoid();
    }
}

generateHelloMethod函數生成的函數是：

       public static void hello() {
             int a = 0xabcd;
             int b = 0xaaaa;
             int c = a - b;
            String s = Integer.toHexString(c);
            System.out.println(s);
            return;
        }

這裏很關鍵的是變量的聲明與賦值和函數的聲明與調用。

例如int變量聲明：
Local a = code.newLocal(TypeId.INT);
變量賦值：
code.loadConstant(a, 0xabcd);
函數聲明：
MethodId

國外原文 ，提供jar下載地址

A Java-language API for doing compile time or runtime code generation targeting the Dalvik VM. Unlike
cglib or ASM, this library creates Dalvik .dex
files instead of Java .class files.

It has a small, close-to-the-metal API. This API mirrors the
Dalvik bytecode specification giving you tight
control over the bytecode emitted. Code is generated instruction-by-instruction; you bring your own abstract
syntax tree if you need one. And since it uses Dalvik’s dx tool as a backend, you get efficient register
allocation and regular/wide instruction selection for free.

Class Proxies

Dexmaker includes a stock code generator for class proxies.
If you just want to do AOP or class mocking, you don’t need to mess around with bytecodes.

Mockito Mocks

Dexmaker includes class proxy support for Mockito. Add the mockito
and the dexmaker .jar files to your Android test project’s libs/ directory and you can use Mockito
in your Android unit tests.

This requires Mockito 1.10.5 or newer.

Runtime Code Generation

This example generates a class and a method. It then loads that class into the current process and invokes its method.

public final class HelloWorldMaker {
    public static void main(String[] args) throws Exception {
        DexMaker dexMaker = new DexMaker();

        // Generate a HelloWorld class.
        TypeId<?> helloWorld = TypeId.get("LHelloWorld;");
        dexMaker.declare(helloWorld, "HelloWorld.generated", Modifier.PUBLIC, TypeId.OBJECT);
        generateHelloMethod(dexMaker, helloWorld);

        // Create the dex file and load it.
        File outputDir = new File(".");
        ClassLoader loader = dexMaker.generateAndLoad(HelloWorldMaker.class.getClassLoader(),
                outputDir, outputDir);
        Class<?> helloWorldClass = loader.loadClass("HelloWorld");

        // Execute our newly-generated code in-process.
        helloWorldClass.getMethod("hello").invoke(null);
    }

    /**
     * Generates Dalvik bytecode equivalent to the following method.
     *    public static void hello() {
     *        int a = 0xabcd;
     *        int b = 0xaaaa;
     *        int c = a - b;
     *        String s = Integer.toHexString(c);
     *        System.out.println(s);
     *        return;
     *    }
     */
    private static void generateHelloMethod(DexMaker dexMaker, TypeId<?> declaringType) {
        // Lookup some types we'll need along the way.
        TypeId<System> systemType = TypeId.get(System.class);
        TypeId<PrintStream> printStreamType = TypeId.get(PrintStream.class);

        // Identify the 'hello()' method on declaringType.
        MethodId hello = declaringType.getMethod(TypeId.VOID, "hello");

        // Declare that method on the dexMaker. Use the returned Code instance
        // as a builder that we can append instructions to.
        Code code = dexMaker.declare(hello, Modifier.STATIC | Modifier.PUBLIC);

        // Declare all the locals we'll need up front. The API requires this.
        Local<Integer> a = code.newLocal(TypeId.INT);
        Local<Integer> b = code.newLocal(TypeId.INT);
        Local<Integer> c = code.newLocal(TypeId.INT);
        Local<String> s = code.newLocal(TypeId.STRING);
        Local<PrintStream> localSystemOut = code.newLocal(printStreamType);

        // int a = 0xabcd;
        code.loadConstant(a, 0xabcd);

        // int b = 0xaaaa;
        code.loadConstant(b, 0xaaaa);

        // int c = a - b;
        code.op(BinaryOp.SUBTRACT, c, a, b);

        // String s = Integer.toHexString(c);
        MethodId<Integer, String> toHexString
                = TypeId.get(Integer.class).getMethod(TypeId.STRING, "toHexString", TypeId.INT);
        code.invokeStatic(toHexString, s, c);

        // System.out.println(s);
        FieldId<System, PrintStream> systemOutField = systemType.getField(printStreamType, "out");
        code.sget(systemOutField, localSystemOut);
        MethodId<PrintStream, Void> printlnMethod = printStreamType.getMethod(
                TypeId.VOID, "println", TypeId.STRING);
        code.invokeVirtual(printlnMethod, null, localSystemOut, s);

        // return;
        code.returnVoid();
    }
}

Use it in your app

Maven users can get dexmaker from Sonatype’s central repository. The Mockito dependency is optional.

<dependency>
    <groupId>com.crittercism.dexmaker</groupId>
    <artifactId>dexmaker</artifactId>
    <version>1.4</version>
</dependency>
<dependency>
    <groupId>com.crittercism.dexmaker</groupId>
    <artifactId>dexmaker-dx</artifactId>
    <version>1.4</version>
</dependency>
<dependency>
    <groupId>com.crittercism.dexmaker</groupId>
    <artifactId>dexmaker-mockito</artifactId>
    <version>1.4</version>
</dependency>

Gradle users can import the project this way:

testCompile "com.crittercism.dexmaker:dexmaker:1.4"
testCompile "com.crittercism.dexmaker:dexmaker-dx:1.4"
testCompile "com.crittercism.dexmaker:dexmaker-mockito:1.4"

Download dexmaker-1.4.jar, dexmaker-dx-1.4.jar
and dexmaker-mockito-1.4.jar.

Run the Unit Tests

The unit tests for dexmaker must be run on a dalvikvm. In order to do this, you can use Vogar in the following fashion:

$ java -jar vogar.jar \
  --mode device \
  --sourcepath /path/to/dexmaker/dexmaker/src/test/java \
  --sourcepath /path/to/dexmaker/dexmaker/src/main/java \
  --sourcepath /path/to/dexmaker/dx/src/main/java \
  --device-dir /data/dexmaker /path/to/dexmaker/dexmaker/src/test/

Download vogar.jar.