动态生成dalvik字节码——dexmaker

元始天尊

https://android.googlesource.com/platform/external/dexmaker.git
该开源项目可以通过编程的方式，把java语义直接转换成android上dalvik字节码，
正常的java代码编译生成class，而要转换成dalvik字节码才能给android使用，
这里介绍的黑科技就是比android上直接加载dex更为底层——直接在android上编译出dalvik字节码再加载
例：
我想生成如下java代码的dalvik字节码：

1. 
   
2. package com.google.dexmaker.examples.Fibonacci;
   
3. 
   
4. public class Fibonacci {
   
5.    public static int fib(int i) {
   
6.      if (i < 2) {
   
7.        return i;
   
8.      }
   
9.      return fib(i - 1) + fib(i - 2);
   
10.    }
    
11. }

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那么我需要写一个对应的逻辑去在android中生成上述逻辑，下面的代码我称为预编译代码

1.        
   
2.         // 对应package com.google.dexmaker.examples.Fibonacci;
   
3.         TypeId<?> fibonacci = TypeId.get("Lcom/google/dexmaker/examples/Fibonacci;");
   
4. 
   
5.         String fileName = "Fibonacci.generated";
   
6.         DexMaker dexMaker = new DexMaker();
   
7.         //对应 public class Fibonacci
   
8.         dexMaker.declare(fibonacci, fileName, Modifier.PUBLIC, TypeId.OBJECT);
   
9. 
   
10.         //对应public static int fib(int i)
    
11.         MethodId<?, Integer> fib = fibonacci.getMethod(TypeId.INT, "fib", TypeId.INT);
    
12.         Code code = dexMaker.declare(fib, Modifier.PUBLIC | Modifier.STATIC);
    
13. 
    
14.         //声明局部变量
    
15.         Local<Integer> i = code.getParameter(0, TypeId.INT);
    
16.         Local<Integer> constant1 = code.newLocal(TypeId.INT);
    
17.         Local<Integer> constant2 = code.newLocal(TypeId.INT);
    
18.         Local<Integer> a = code.newLocal(TypeId.INT);
    
19.         Local<Integer> b = code.newLocal(TypeId.INT);
    
20.         Local<Integer> c = code.newLocal(TypeId.INT);
    
21.         Local<Integer> d = code.newLocal(TypeId.INT);
    
22.         Local<Integer> result = code.newLocal(TypeId.INT);
    
23. 
    
24.         code.loadConstant(constant1, 1);//=1
    
25.         code.loadConstant(constant2, 2);//=2
    
26.         Label baseCase = new Label();
    
27.         code.compare(Comparison.LT, baseCase, i, constant2);//if (i < 2) {
    
28.         code.op(BinaryOp.SUBTRACT, a, i, constant1);//fib(i - 1)
    
29.         code.op(BinaryOp.SUBTRACT, b, i, constant2);//fib(i - 2)
    
30.         code.invokeStatic(fib, c, a);
    
31.         code.invokeStatic(fib, d, b);
    
32.         code.op(BinaryOp.ADD, result, c, d);
    
33.         code.returnValue(result);//return fib(i - 1) + fib(i - 2);
    
34.         code.mark(baseCase);//}
    
35.         code.returnValue(i);//return i
    
36. 
    

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全部代码

1. /*
   
2. * Copyright (C) 2012 The Android Open Source Project
   
3. *
   
4. * Licensed under the Apache License, Version 2.0 (the "License");
   
5. * you may not use this file except in compliance with the License.
   
6. * You may obtain a copy of the License at
   
7. *
   
8. *      [url]http://www.apache.org/licenses/LICENSE-2.0[/url]
   
9. *
   
10. * Unless required by applicable law or agreed to in writing, software
    
11. * distributed under the License is distributed on an "AS IS" BASIS,
    
12. * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    
13. * See the License for the specific language governing permissions and
    
14. * limitations under the License.
    
15. */
    
16. 
    
17. package example;
    
18. 
    
19. import com.google.dexmaker.BinaryOp;
    
20. import com.google.dexmaker.Code;
    
21. import com.google.dexmaker.Comparison;
    
22. import com.google.dexmaker.DexMaker;
    
23. import com.google.dexmaker.Label;
    
24. import com.google.dexmaker.Local;
    
25. import com.google.dexmaker.MethodId;
    
26. import com.google.dexmaker.TypeId;
    
27. import java.io.File;
    
28. import java.lang.reflect.Method;
    
29. import java.lang.reflect.Modifier;
    
30. 
    
31. public final class FibonacciMaker {
    
32.     public static void main(String[] args) throws Exception {
    
33.         TypeId<?> fibonacci = TypeId.get("Lcom/google/dexmaker/examples/Fibonacci;");
    
34. 
    
35.         String fileName = "Fibonacci.generated";
    
36.         DexMaker dexMaker = new DexMaker();
    
37.         dexMaker.declare(fibonacci, fileName, Modifier.PUBLIC, TypeId.OBJECT);
    
38. 
    
39.         MethodId<?, Integer> fib = fibonacci.getMethod(TypeId.INT, "fib", TypeId.INT);
    
40.         Code code = dexMaker.declare(fib, Modifier.PUBLIC | Modifier.STATIC);
    
41. 
    
42.         Local<Integer> i = code.getParameter(0, TypeId.INT);
    
43.         Local<Integer> constant1 = code.newLocal(TypeId.INT);
    
44.         Local<Integer> constant2 = code.newLocal(TypeId.INT);
    
45.         Local<Integer> a = code.newLocal(TypeId.INT);
    
46.         Local<Integer> b = code.newLocal(TypeId.INT);
    
47.         Local<Integer> c = code.newLocal(TypeId.INT);
    
48.         Local<Integer> d = code.newLocal(TypeId.INT);
    
49.         Local<Integer> result = code.newLocal(TypeId.INT);
    
50. 
    
51.         code.loadConstant(constant1, 1);
    
52.         code.loadConstant(constant2, 2);
    
53.         Label baseCase = new Label();
    
54.         code.compare(Comparison.LT, baseCase, i, constant2);
    
55.         code.op(BinaryOp.SUBTRACT, a, i, constant1);
    
56.         code.op(BinaryOp.SUBTRACT, b, i, constant2);
    
57.         code.invokeStatic(fib, c, a);
    
58.         code.invokeStatic(fib, d, b);
    
59.         code.op(BinaryOp.ADD, result, c, d);
    
60.         code.returnValue(result);
    
61.         code.mark(baseCase);
    
62.         code.returnValue(i);
    
63. 
    
64.         ClassLoader loader = dexMaker.generateAndLoad(
    
65.                 FibonacciMaker.class.getClassLoader(), getDataDirectory());
    
66. 
    
67.         Class<?> fibonacciClass = loader.loadClass("com.google.dexmaker.examples.Fibonacci");
    
68.         Method fibMethod = fibonacciClass.getMethod("fib", int.class);
    
69.         System.out.println(fibMethod.invoke(null, 8));
    
70.     }
    
71. 
    
72.     public static File getDataDirectory() {
    
73.         String envVariable = "ANDROID_DATA";
    
74.         String defaultLoc = "/data";
    
75.         String path = System.getenv(envVariable);
    
76.         return path == null ? new File(defaultLoc) : new File(path);
    
77.     }
    
78. }
    

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应该可以建立一个翻译工具，将java代码翻译为上面的预编译代码，从而实现动态下载java代码，在android上运行