一、dexmaker简单介绍
dexmaker是运行在Android Dalvik VM上,利用Java编写,来动态生成DEX字节码的API。如果读者了解AOP编程的话,应该听说过cglib or ASM,但这两个工具生成都是Java字节码,而Dalvik加载的必须是DEX字节码。所以,想要在Android上进行AOP编程,dexmaker可以说是一个很好的选择。项目地址:https://github.com/crittercism/dexmaker。
二。简单使用
下面这个例子非常典型,可以说入门非常好了。过程很简单,生成一个包含一个函数的类,在主程序里面动态加载(使用ClassLoader),然后执行类里面的函数。这是在Java平台的例子,我直接在Android上进行编程的,后面或说明相应的问题以及解决办法,下来看看这个例子吧。
1 public final class HelloWorldMaker {
2 public static void main(String[] args) throws Exception {
3 DexMaker dexMaker = new DexMaker();
4
5 // Generate a HelloWorld class.
6 TypeId helloWorld = TypeId.get("LHelloWorld;");
7 dexMaker.declare(helloWorld, "HelloWorld.generated", Modifier.PUBLIC, TypeId.OBJECT);
8 generateHelloMethod(dexMaker, helloWorld);
9
10 // Create the dex file and load it.
11 File outputDir = new File(".");
12 ClassLoader loader = dexMaker.generateAndLoad(HelloWorldMaker.class.getClassLoader(),
13 outputDir, outputDir);
14 Class helloWorldClass = loader.loadClass("HelloWorld");
15
16 // Execute our newly-generated code in-process.
17 helloWorldClass.getMethod("hello").invoke(null);
18 }
19
20 private static void generateHelloMethod(DexMaker dexMaker, TypeId declaringType) {
21 // Lookup some types we'll need along the way.
22 TypeId systemType = TypeId.get(System.class);
23 TypeId printStreamType = TypeId.get(PrintStream.class);
24
25 // Identify the 'hello()' method on declaringType.
26 MethodId hello = declaringType.getMethod(TypeId.VOID, "hello");
27
28 // Declare that method on the dexMaker. Use the returned Code instance
29 // as a builder that we can append instructions to.
30 Code code = dexMaker.declare(hello, Modifier.STATIC | Modifier.PUBLIC);
31
32 // Declare all the locals we'll need up front. The API requires this.
33 Local a = code.newLocal(TypeId.INT);
34 Local b = code.newLocal(TypeId.INT);
35 Local c = code.newLocal(TypeId.INT);
36 Local s = code.newLocal(TypeId.STRING);
37 Local localSystemOut = code.newLocal(printStreamType);
38
39 // int a = 0xabcd;
40 code.loadConstant(a, 0xabcd);
41
42 // int b = 0xaaaa;
43 code.loadConstant(b, 0xaaaa);
44
45 // int c = a - b;
46 code.op(BinaryOp.SUBTRACT, c, a, b);
47
48 // String s = Integer.toHexString(c);
49 MethodId toHexString
50 = TypeId.get(Integer.class).getMethod(TypeId.STRING, "toHexString", TypeId.INT);
51 code.invokeStatic(toHexString, s, c);
52
53 // System.out.println(s);
54 FieldId systemOutField = systemType.getField(printStreamType, "out");
55 code.sget(systemOutField, localSystemOut);
56 MethodId printlnMethod = printStreamType.getMethod(
57 TypeId.VOID, "println", TypeId.STRING);
58 code.invokeVirtual(printlnMethod, null, localSystemOut, s);
59
60 // return;
61 code.returnVoid();
62 }
63 }
generateHelloMethod函数生成的函数是:
1 public static void hello() { 2 int a = 0xabcd; 3 int b = 0xaaaa; 4 int c = a - b; 5 String s = Integer.toHexString(c); 6 System.out.println(s); 7 return; 8 }
这里很关键的是变量的声明与赋值和函数的声明与调用
。例如int
变量声明:
1 Locala = code.newLocal(TypeId.INT);
变量赋值:
1 code.loadConstant(a, 0xabcd);
函数声明:
1 MethodIdtoHexString = TypeId.get(Integer.class).getMethod(TypeId.STRING, "toHexString", TypeId.INT);
函数调用:
1 code.invokeStatic(toHexString, s, c);
过程非常简单,要生成一个完整的简单的类按照此步骤能很快完成。好的,现在进入正片部分了,即在Android平台使用dexmaker的情况。