Android动态类生成预加载-dexmaker使用

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<System> systemType = TypeId.get(System.class);
23         TypeId<PrintStream> 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<Integer> a = code.newLocal(TypeId.INT);
34         Local<Integer> b = code.newLocal(TypeId.INT);
35         Local<Integer> c = code.newLocal(TypeId.INT);
36         Local<String> s = code.newLocal(TypeId.STRING);
37         Local<PrintStream> 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<Integer, String> 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<System, PrintStream> systemOutField = systemType.getField(printStreamType, "out");
55         code.sget(systemOutField, localSystemOut);
56         MethodId<PrintStream, Void> 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 Local<Integer> a = code.newLocal(TypeId.INT); 

变量赋值:
 1 code.loadConstant(a, 0xabcd); 

函数声明:
 1 MethodId<Integer, String> toHexString = 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。

posted @ 2015-06-29 17:13  Harold Tihan  阅读(2149)  评论(0编辑  收藏