第 8 回 リフレクションに取って代わるコード生成

public class HolderBean
{
    private int m_value1;
    private int m_value2;
    public int getValue1() {
        return m_value1;
    }
    public void setValue1(int value) {
        m_value1 = value;
    }
    public int getValue2() {
        return m_value2;
    }
    public void setValue2(int value) {
        m_value2 = value;
    }
}
public class ReflectAccess
{
    public void run(String[] args) throws Exception {
        if (args.length == 1 & args[0].length() > 0) {
            // create property name
            char lead = args[0].charAt(0);
            String pname = Character.toUpperCase(lead) +
                args[0].substring(1);
            // look up the get and set methods
            Method gmeth = HolderBean.class.getDeclaredMethod
                ("get" + pname, new Class[0]);
            Method smeth = HolderBean.class.getDeclaredMethod
                ("set" + pname, new Class[] { int.class });
            // increment value using reflection
            HolderBean bean = new HolderBean();
            Object start = gmeth.invoke(bean, null);
            int incr = ((Integer)start).intValue() + 1;
            smeth.invoke(bean, new Object[] {new Integer(incr)});
            // print the ending values
            System.out.println("Result values " +
                bean.getValue1() + ", " + bean.getValue2());
            } else {
            System.out.println("Usage: ReflectAccess value1|value2");
        }
    }
}

[dennis]$ java -cp . ReflectAccess value1
Result values 1, 0
[dennis]$ java -cp . ReflectAccess value2
Result values 0, 1

public interface IAccess
{
    public void setTarget(Object target);
    public int getValue();
    public void setValue(int value);
}

public class AccessValue1 implements IAccess
{
    private HolderBean m_target;
    public void setTarget(Object target) {
        m_target = (HolderBean)target;
    }
    public int getValue() {
        return m_target.getValue1();
    }
    public void setValue(int value) {
        m_target.setValue1(value);
    }
}

/** Parameter types for call with no parameters. */
private static final CtClass[] NO_ARGS = {};
/** Parameter types for call with single int value. */
private static final CtClass[] INT_ARGS = { CtClass.intType };
protected byte[] createAccess(Class tclas, Method gmeth,
    Method smeth, String cname) throws Exception {
      // build generator for the new class
      String tname = tclas.getName();
      ClassPool pool = ClassPool.getDefault();
      CtClass clas = pool.makeClass(cname);
      clas.addInterface(pool.get("IAccess"));
      CtClass target = pool.get(tname);
      // add target object field to class
      CtField field = new CtField(target, "m_target", clas);
      clas.addField(field);
      // add public default constructor method to class
      CtConstructor cons = new CtConstructor(NO_ARGS, clas);
      cons.setBody(";");
      clas.addConstructor(cons);
      // add public setTarget method
      CtMethod meth = new CtMethod(CtClass.voidType, "setTarget",
          new CtClass[] { pool.get("java.lang.Object") }, clas);
      meth.setBody("m_target = (" + tclas.getName() + ")$1;");
      clas.addMethod(meth);
      // add public getValue method
      meth = new CtMethod(CtClass.intType, "getValue", NO_ARGS, clas);
      meth.setBody("return m_target." + gmeth.getName() + "();");
      clas.addMethod(meth);
      // add public setValue method
      meth = new CtMethod(CtClass.voidType, "setValue", INT_ARGS, clas);
      meth.setBody("m_target." + smeth.getName() + "($1);");
      clas.addMethod(meth);
      // return binary representation of completed class
      return clas.toBytecode();
}

/** Parameter types for call with single int value. */
    private static final Type[] INT_ARGS = { Type.INT };
/** Utility method for adding constructed method to class. */
private static void addMethod(MethodGen mgen, ClassGen cgen) {
    mgen.setMaxStack();
    mgen.setMaxLocals();
    InstructionList ilist = mgen.getInstructionList();
    Method method = mgen.getMethod();
    ilist.dispose();
    cgen.addMethod(method);
}
protected byte[] createAccess(Class tclas,
    java.lang.reflect.Method gmeth, java.lang.reflect.Method smeth,
    String cname) {
    // build generators for the new class
    String tname = tclas.getName();
    ClassGen cgen = new ClassGen(cname, "java.lang.Object",
        cname + ".java", Constants.ACC_PUBLIC,
        new String[] { "IAccess" });
    InstructionFactory ifact = new InstructionFactory(cgen);
    ConstantPoolGen pgen = cgen.getConstantPool();
    //. add target object field to class
    FieldGen fgen = new FieldGen(Constants.ACC_PRIVATE,
        new ObjectType(tname), "m_target", pgen);
    cgen.addField(fgen.getField());
    int findex = pgen.addFieldref(cname, "m_target",
        Utility.getSignature(tname));
    // create instruction list for default constructor
    InstructionList ilist = new InstructionList();
    ilist.append(InstructionConstants.ALOAD_0);
    ilist.append(ifact.createInvoke("java.lang.Object", "<init>",
        Type.VOID, Type.NO_ARGS, Constants.INVOKESPECIAL));
    ilist.append(InstructionFactory.createReturn(Type.VOID));
    // add public default constructor method to class
    MethodGen mgen = new MethodGen(Constants.ACC_PUBLIC, Type.VOID,
        Type.NO_ARGS, null, "<init>", cname, ilist, pgen);
    addMethod(mgen, cgen);
    // create instruction list for setTarget method
    ilist = new InstructionList();
    ilist.append(InstructionConstants.ALOAD_0);
    ilist.append(InstructionConstants.ALOAD_1);
    ilist.append(new CHECKCAST(pgen.addClass(tname)));
    ilist.append(new PUTFIELD(findex));
    ilist.append(InstructionConstants.RETURN);
    // add public setTarget method
    mgen = new MethodGen(Constants.ACC_PUBLIC, Type.VOID,
        new Type[] { Type.OBJECT }, null, "setTarget", cname,
        ilist, pgen);
    addMethod(mgen, cgen);
    // create instruction list for getValue method
    ilist = new InstructionList();
    ilist.append(InstructionConstants.ALOAD_0);
    ilist.append(new GETFIELD(findex));
    ilist.append(ifact.createInvoke(tname, gmeth.getName(),
        Type.INT, Type.NO_ARGS, Constants.INVOKEVIRTUAL));
    ilist.append(InstructionConstants.IRETURN);
    // add public getValue method
    mgen = new MethodGen(Constants.ACC_PUBLIC, Type.INT,
        Type.NO_ARGS, null, "getValue", cname, ilist, pgen);
    addMethod(mgen, cgen);
    // create instruction list for setValue method
    ilist = new InstructionList();
    ilist.append(InstructionConstants.ALOAD_0);
    ilist.append(new GETFIELD(findex));
    ilist.append(InstructionConstants.ILOAD_1);
    ilist.append(ifact.createInvoke(tname, smeth.getName(),
        Type.VOID, INT_ARGS, Constants.INVOKEVIRTUAL));
    ilist.append(InstructionConstants.RETURN);
    // add public setValue method
    mgen = new MethodGen(Constants.ACC_PUBLIC, Type.VOID,
        INT_ARGS, null, "setValue", cname, ilist, pgen);
    addMethod(mgen, cgen);
    // return bytecode of completed class
    return cgen.getJavaClass().getBytes();
}

/** Run timed loop using reflection for access to value. */
private int runReflection(int num, Method gmeth, Method smeth,
    Object obj) {
    int value = 0;
    try {
        Object[] gargs = new Object[0];
        Object[] sargs = new Object[1];
        for (int i = 0; i < num; i++) {
            // messy usage of Integer values required in loop
            Object result = gmeth.invoke(obj, gargs);
            value = ((Integer)result).intValue() + 1;
            sargs[0] = new Integer(value);
            smeth.invoke(obj, sargs);
            }
    } catch (Exception ex) {
        ex.printStackTrace(System.err);
        System.exit(1);
    }
    return value;
}
/** Run timed loop using generated class for access to value. */
private int runAccess(int num, IAccess access, Object obj) {
    access.setTarget(obj);
    int value = 0;
    for (int i = 0; i < num; i++) {
        value = access.getValue() + 1;
        access.setValue(value);
    }
    return value;
}
public void run(String name, int count) throws Exception {
    // get instance and access methods
    HolderBean bean = new HolderBean();
    String pname = name;
    char lead = pname.charAt(0);
    pname = Character.toUpperCase(lead) + pname.substring(1);
    Method gmeth = null;
    Method smeth = null;
    try {
        gmeth = HolderBean.class.getDeclaredMethod("get" + pname,
            new Class[0]);
        smeth = HolderBean.class.getDeclaredMethod("set" + pname,
            new Class[] { int.class });
    } catch (Exception ex) {
        System.err.println("No methods found for property " + pname);
        ex.printStackTrace(System.err);
        return;
    }
    // create the access class as a byte array
    long base = System.currentTimeMillis();
    String cname = "IAccess$impl_HolderBean_" + gmeth.getName() +
        "_" + smeth.getName();
    byte[] bytes = createAccess(HolderBean.class, gmeth, smeth, cname);
    // load and construct an instance of the class
    Class clas = s_classLoader.load(cname, bytes);
    IAccess access = null;
    try {
        access = (IAccess)clas.newInstance();
    } catch (IllegalAccessException ex) {
        ex.printStackTrace(System.err);
        System.exit(1);
    } catch (InstantiationException ex) {
        ex.printStackTrace(System.err);
        System.exit(1);
    }
    System.out.println("Generate and load time of " +
        (System.currentTimeMillis()-base) + " ms.");
    // run the timing comparison
    long start = System.currentTimeMillis();
    int result = runReflection(count, gmeth, smeth, bean);
    long time = System.currentTimeMillis() - start;
    System.out.println("Reflection took " + time +
        " ms. with result " + result + " (" + bean.getValue1() +
        ", " + bean.getValue2() + ")");
    bean.setValue1(0);
    bean.setValue2(0);
    start = System.currentTimeMillis();
    result = runAccess(count, access, bean);
    time = System.currentTimeMillis() - start;
    System.out.println("Generated took " + time +
        " ms. with result " + result + " (" + bean.getValue1() +
        ", " + bean.getValue2() + ")");
}
/** Simple-minded loader for constructed classes. */
protected static class DirectLoader extends SecureClassLoader
{
    protected DirectLoader() {
        super(TimeCalls.class.getClassLoader());
    }
    protected Class load(String name, byte[] data) {
        return super.defineClass(name, data, 0, data.length);
    }
}

[dennis]$$ java -cp .:bcel.jar BCELCalls 2000
Generate and load time of 409 ms.
Reflection took 61 ms. with result 2000 (2000, 0)
Generated took 2 ms. with result 2000 (2000, 0)
Generate and load time of 1 ms.
Reflection took 13 ms. with result 2000 (0, 2000)
Generated took 2 ms. with result 2000 (0, 2000)