ctnewmethod.java

Javassist是一个开源的分析、编辑和创建Java字节码的类库。是由东京技术学院的数学和计算机科学系的 Shigeru Chiba 所创建的。它已加入了开放源代码JBoss 应用服务器项目,通过使

            code.addReturn(field.getType());
        }
        catch (NotFoundException e) {
            throw new CannotCompileException(e);
        }

        minfo.setCodeAttribute(code.toCodeAttribute());
        return new CtMethod(minfo, field.getDeclaringClass());
    }

    /**
     * Creates a public setter method.  The setter method assigns the
     * value of the first parameter to the specified field
     * in the class to which this method is added.
     * The created method is not static even if the field is
     * static.  You may not change it to be static
     * by <code>setModifiers()</code> in <code>CtBehavior</code>.
     *
     * @param methodName        the name of the setter
     * @param field             the field accessed.
     */
    public static CtMethod setter(String methodName, CtField field)
        throws CannotCompileException
    {
        FieldInfo finfo = field.getFieldInfo2();
        String fieldType = finfo.getDescriptor();
        String desc = "(" + fieldType + ")V";
        ConstPool cp = finfo.getConstPool();
        MethodInfo minfo = new MethodInfo(cp, methodName, desc);
        minfo.setAccessFlags(AccessFlag.PUBLIC);

        Bytecode code = new Bytecode(cp, 3, 3);
        try {
            String fieldName = finfo.getName();
            if ((finfo.getAccessFlags() & AccessFlag.STATIC) == 0) {
                code.addAload(0);
                code.addLoad(1, field.getType());
                code.addPutfield(Bytecode.THIS, fieldName, fieldType);
            }
            else {
                code.addLoad(1, field.getType());
                code.addPutstatic(Bytecode.THIS, fieldName, fieldType);
            }

            code.addReturn(null);
        }
        catch (NotFoundException e) {
            throw new CannotCompileException(e);
        }

        minfo.setCodeAttribute(code.toCodeAttribute());
        return new CtMethod(minfo, field.getDeclaringClass());
    }

    /**
     * Creates a method forwarding to a delegate in
     * a super class.  The created method calls a method specified
     * by <code>delegate</code> with all the parameters passed to the
     * created method.  If the delegate method returns a value,
     * the created method returns that value to the caller.
     * The delegate method must be declared in a super class.
     *
     * <p>The following method is an example of the created method.
     *
     * <ul><pre>int f(int p, int q) {
     *     return super.f(p, q);
     * }</pre></ul>
     *
     * <p>The name of the created method can be changed by
     * <code>setName()</code>.
     *
     * @param delegate    the method that the created method forwards to.
     * @param declaring         the class to which the created method is
     *                          added.
     */
    public static CtMethod delegator(CtMethod delegate, CtClass declaring)
        throws CannotCompileException
    {
        try {
            return delegator0(delegate, declaring);
        }
        catch (NotFoundException e) {
            throw new CannotCompileException(e);
        }
    }

    private static CtMethod delegator0(CtMethod delegate, CtClass declaring)
        throws CannotCompileException, NotFoundException
    {
        MethodInfo deleInfo = delegate.getMethodInfo2();
        String methodName = deleInfo.getName();
        String desc = deleInfo.getDescriptor();
        ConstPool cp = declaring.getClassFile2().getConstPool();
        MethodInfo minfo = new MethodInfo(cp, methodName, desc);
        minfo.setAccessFlags(deleInfo.getAccessFlags());

        ExceptionsAttribute eattr = deleInfo.getExceptionsAttribute();
        if (eattr != null)
            minfo.setExceptionsAttribute(
                                (ExceptionsAttribute)eattr.copy(cp, null));

        Bytecode code = new Bytecode(cp, 0, 0);
        boolean isStatic = Modifier.isStatic(delegate.getModifiers());
        CtClass deleClass = delegate.getDeclaringClass();
        CtClass[] params = delegate.getParameterTypes();
        int s;
        if (isStatic) {
            s = code.addLoadParameters(params, 0);
            code.addInvokestatic(deleClass, methodName, desc);
        }
        else {
            code.addLoad(0, deleClass);
            s = code.addLoadParameters(params, 1);
            code.addInvokespecial(deleClass, methodName, desc);
        }

        code.addReturn(delegate.getReturnType());
        code.setMaxLocals(++s);
        code.setMaxStack(s < 2 ? 2 : s); // for a 2-word return value
        minfo.setCodeAttribute(code.toCodeAttribute());
        return new CtMethod(minfo, declaring);
    }

    /**
     * Creates a wrapped method.  The wrapped method receives parameters
     * in the form of an array of <code>Object</code>.
     *
     * <p>The body of the created method is a copy of the body of a method
     * specified by <code>body</code>.  However, it is wrapped in
     * parameter-conversion code.
     *
     * <p>The method specified by <code>body</code> must have this singature:
     *
     * <ul><code>Object method(Object[] params, &lt;type&gt; cvalue)
     * </code></ul>
     *
     * <p>The type of the <code>cvalue</code> depends on
     * <code>constParam</code>.
     * If <code>constParam</code> is <code>null</code>, the signature
     * must be:
     *
     * <ul><code>Object method(Object[] params)</code></ul>
     *
     * <p>The method body copied from <code>body</code> is wrapped in
     * parameter-conversion code, which converts parameters specified by
     * <code>parameterTypes</code> into an array of <code>Object</code>.
     * The returned value is also converted from the <code>Object</code>
     * type to the type specified by <code>returnType</code>.  Thus,
     * the resulting method body is as follows:
     *
     * <ul><pre>Object[] params = new Object[] { p0, p1, ... };
     * &lt;<i>type</i>&gt; cvalue = &lt;<i>constant-value</i>&gt;;
     *  <i>... copied method body ...</i>
     * Object result = &lt;<i>returned value</i>&gt;
     * return (<i>&lt;returnType&gt;</i>)result;
     * </pre></ul>
     *
     * <p>The variables <code>p0</code>, <code>p2</code>, ... represent
     * formal parameters of the created method.
     * The value of <code>cvalue</code> is specified by
     * <code>constParam</code>.
     *
     * <p>If the type of a parameter or a returned value is a primitive
     * type, then the value is converted into a wrapper object such as
     * <code>java.lang.Integer</code>.  If the type of the returned value
     * is <code>void</code>, the returned value is discarded.
     *
     * <p><i>Example:</i>
     *
     * <ul><pre>ClassPool pool = ... ;
     * CtClass vec = pool.makeClass("intVector");
     * vec.setSuperclass(pool.get("java.util.Vector"));
     * CtMethod addMethod = pool.getMethod("Sample", "add0");
     *
     * CtClass[] argTypes = { CtClass.intType };
     * CtMethod m = CtNewMethod.wrapped(CtClass.voidType, "add", argTypes,
     *                                  null, addMethod, null, vec);
     * vec.addMethod(m);</pre></ul>
     *
     * <p>where the class <code>Sample</code> is as follows:
     *
     * <ul><pre>public class Sample extends java.util.Vector {
     *     public Object add0(Object[] args) {
     *         super.addElement(args[0]);
     *         return null;
     *     }
     * }</pre></ul>
     *
     * <p>This program produces a class <code>intVector</code>:
     *
     * <ul><pre>public class intVector extends java.util.Vector {
     *     public void add(int p0) {
     *         Object[] args = new Object[] { p0 };
     *         // begin of copied body
     *         super.addElement(args[0]);
     *         Object result = null;
     *         // end
     *     }
     * }</pre></ul>
     *
     * <p>Note that the type of the parameter to <code>add()</code> depends
     * only on the value of <code>argTypes</code> passed to
     * <code>CtNewMethod.wrapped()</code>.  Thus, it is easy to
     * modify this program to produce a
     * <code>StringVector</code> class, which is a vector containing
     * only <code>String</code> objects, and other vector classes.
     *
     * @param returnType        the type of the returned value.
     * @param mname             the method name.
     * @param parameterTypes    a list of the parameter types.
     * @param exceptionTypes    a list of the exception types.
     * @param body              the method body
     *                          (must not be a static method).
     * @param constParam        the constant parameter
     *                          (maybe <code>null</code>).
     * @param declaring         the class to which the created method is
     *                          added.
     */
    public static CtMethod wrapped(CtClass returnType,
                                   String mname,
                                   CtClass[] parameterTypes,
                                   CtClass[] exceptionTypes,
                                   CtMethod body, ConstParameter constParam,
                                   CtClass declaring)
        throws CannotCompileException
    {
        return CtNewWrappedMethod.wrapped(returnType, mname, parameterTypes,
                        exceptionTypes, body, constParam, declaring);
    }
}