ctbehavior.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

        throws CannotCompileException
    {
        declaringClass.checkModify();
        try {
            Javac jv = new Javac(declaringClass);
            if (delegateMethod != null)
                jv.recordProceed(delegateObj, delegateMethod);

            Bytecode b = jv.compileBody(this, src);
            methodInfo.setCodeAttribute(b.toCodeAttribute());
            methodInfo.setAccessFlags(methodInfo.getAccessFlags()
                                      & ~AccessFlag.ABSTRACT);
        }
        catch (CompileError e) {
            throw new CannotCompileException(e);
        }
    }

    static void setBody0(CtClass srcClass, MethodInfo srcInfo,
                         CtClass destClass, MethodInfo destInfo,
                         ClassMap map)
        throws CannotCompileException
    {
        destClass.checkModify();

        map = new ClassMap(map);
        map.put(srcClass.getName(), destClass.getName());
        try {
            CodeAttribute cattr = srcInfo.getCodeAttribute();
            if (cattr != null) {
                ConstPool cp = destInfo.getConstPool();
                CodeAttribute ca = (CodeAttribute)cattr.copy(cp, map);
                destInfo.setCodeAttribute(ca);
            }
        }
        catch (CodeAttribute.RuntimeCopyException e) {
            /* the exception may be thrown by copy() in CodeAttribute.
             */
            throw new CannotCompileException(e);
        }

        destInfo.setAccessFlags(destInfo.getAccessFlags()
                                & ~AccessFlag.ABSTRACT);
    }

    /**
     * Obtains an attribute with the given name.
     * If that attribute is not found in the class file, this
     * method returns null.
     *
     * <p>Note that an attribute is a data block specified by
     * the class file format.  It is not an annotation.
     * See {@link javassist.bytecode.AttributeInfo}.
     *
     * @param name              attribute name
     */
    public byte[] getAttribute(String name) {
        AttributeInfo ai = methodInfo.getAttribute(name);
        if (ai == null)
            return null;
        else
            return ai.get();
    }

    /**
     * Adds an attribute. The attribute is saved in the class file.
     *
     * <p>Note that an attribute is a data block specified by
     * the class file format.  It is not an annotation.
     * See {@link javassist.bytecode.AttributeInfo}.
     *
     * @param name      attribute name
     * @param data      attribute value
     */
    public void setAttribute(String name, byte[] data) {
        declaringClass.checkModify();
        methodInfo.addAttribute(new AttributeInfo(methodInfo.getConstPool(),
                                                  name, data));
    }

    /**
     * Declares to use <code>$cflow</code> for this method/constructor.
     * If <code>$cflow</code> is used, the class files modified
     * with Javassist requires a support class
     * <code>javassist.runtime.Cflow</code> at runtime
     * (other Javassist classes are not required at runtime).
     *
     * <p>Every <code>$cflow</code> variable is given a unique name.
     * For example, if the given name is <code>"Point.paint"</code>,
     * then the variable is indicated by <code>$cflow(Point.paint)</code>.
     *
     * @param name      <code>$cflow</code> name.  It can include
     *                  alphabets, numbers, <code>_</code>,
     *                  <code>$</code>, and <code>.</code> (dot).
     *
     * @see javassist.runtime.Cflow
     */
    public void useCflow(String name) throws CannotCompileException {
        CtClass cc = declaringClass;
        cc.checkModify();
        ClassPool pool = cc.getClassPool();
        String fname;
        int i = 0;
        while (true) {
            fname = "_cflow$" + i++;
            try {
                cc.getDeclaredField(fname);
            }
            catch(NotFoundException e) {
                break;
            }
        }

        pool.recordCflow(name, declaringClass.getName(), fname);
        try {
            CtClass type = pool.get("javassist.runtime.Cflow");
            CtField field = new CtField(type, fname, cc);
            field.setModifiers(Modifier.PUBLIC | Modifier.STATIC);
            cc.addField(field, CtField.Initializer.byNew(type));
            insertBefore(fname + ".enter();");
            String src = fname + ".exit();";
            insertAfter(src, true);
        }
        catch (NotFoundException e) {
            throw new CannotCompileException(e);
        }
    }

    /**
     * Declares a new local variable.  The scope of this variable is the
     * whole method body.  The initial value of that variable is not set.
     * The declared variable can be accessed in the code snippet inserted
     * by <code>insertBefore()</code>, <code>insertAfter()</code>, etc.
     *
     * <p>If the second parameter <code>asFinally</code> to
     * <code>insertAfter()</code> is true, the declared local variable
     * is not visible from the code inserted by <code>insertAfter()</code>.
     *
     * @param name      the name of the variable
     * @param type      the type of the variable
     * @see #insertBefore(String)
     * @see #insertAfter(String)
     */
    public void addLocalVariable(String name, CtClass type)
        throws CannotCompileException
    {
        declaringClass.checkModify();
        ConstPool cp = methodInfo.getConstPool();
        CodeAttribute ca = methodInfo.getCodeAttribute();
        if (ca == null)
            throw new CannotCompileException("no method body");

        LocalVariableAttribute va = (LocalVariableAttribute)ca.getAttribute(
                                                LocalVariableAttribute.tag);
        if (va == null) {
            va = new LocalVariableAttribute(cp);
            ca.getAttributes().add(va);
        }

        int maxLocals = ca.getMaxLocals();
        String desc = Descriptor.of(type);
        va.addEntry(0, ca.getCodeLength(),
                    cp.addUtf8Info(name), cp.addUtf8Info(desc), maxLocals);
        ca.setMaxLocals(maxLocals + Descriptor.dataSize(desc));
    }

    /**
     * Modifies the method/constructor body.
     *
     * @param converter         specifies how to modify.
     */
    public void instrument(CodeConverter converter)
        throws CannotCompileException
    {
        declaringClass.checkModify();
        ConstPool cp = methodInfo.getConstPool();
        converter.doit(getDeclaringClass(), methodInfo, cp);
    }

    /**
     * Modifies the method/constructor body.
     *
     * @param editor            specifies how to modify.
     */
    public void instrument(ExprEditor editor)
        throws CannotCompileException
    {
        // if the class is not frozen,
        // does not turn the modified flag on.
        if (declaringClass.isFrozen())
            declaringClass.checkModify();

        if (editor.doit(declaringClass, methodInfo))
            declaringClass.checkModify();
    }

    /**
     * Inserts bytecode at the beginning of the body.
     *
     * <p>If this object represents a constructor,
     * the bytecode is inserted before
     * a constructor in the super class or this class is called.
     * Therefore, the inserted bytecode is subject to constraints described
     * in Section 4.8.2 of The Java Virtual Machine Specification (2nd ed).
     * For example, it cannot access instance fields or methods although
     * it may assign a value to an instance field directly declared in this
     * class.  Accessing static fields and methods is allowed.
     * Use <code>insertBeforeBody()</code> in <code>CtConstructor</code>.
     *
     * @param src       the source code representing the inserted bytecode.
     *                  It must be a single statement or block.
     * @see CtConstructor#insertBeforeBody(String)
     */
    public void insertBefore(String src) throws CannotCompileException {
        declaringClass.checkModify();
        CodeAttribute ca = methodInfo.getCodeAttribute();
        if (ca == null)
            throw new CannotCompileException("no method body");

        CodeIterator iterator = ca.iterator();
        Javac jv = new Javac(declaringClass);
        try {
            int nvars = jv.recordParams(getParameterTypes(),
                                        Modifier.isStatic(getModifiers()));
            jv.recordParamNames(ca, nvars);
            jv.recordLocalVariables(ca, 0);
            jv.compileStmnt(src);
            Bytecode b = jv.getBytecode();
            int stack = b.getMaxStack();
            int locals = b.getMaxLocals();

            if (stack > ca.getMaxStack())
                ca.setMaxStack(stack);

            if (locals > ca.getMaxLocals())
                ca.setMaxLocals(locals);

            int pos = iterator.insertEx(b.get());
            iterator.insert(b.getExceptionTable(), pos);
        }
        catch (NotFoundException e) {
            throw new CannotCompileException(e);
        }
        catch (CompileError e) {
            throw new CannotCompileException(e);
        }
        catch (BadBytecode e) {
            throw new CannotCompileException(e);
        }
    }

    /**
     * Inserts bytecode at the end of the body.
     * The bytecode is inserted just before every return insturction.
     * It is not executed when an exception is thrown.
     *
     * @param src       the source code representing the inserted bytecode.
     *                  It must be a single statement or block.
     */
    public void insertAfter(String src)
        throws CannotCompileException
    {
        insertAfter(src, false);
    }

    /**
     * Inserts bytecode at the end of the body.
     * The bytecode is inserted just before every return insturction.
     *
     * @param src       the source code representing the inserted bytecode.
     *                  It must be a single statement or block.
     * @param asFinally         true if the inserted bytecode is executed
     *                  not only when the control normally returns
     *                  but also when an exception is thrown.
     *                  If this parameter is true, the inserted code cannot
     *                  access local variables.
     */
    public void insertAfter(String src, boolean asFinally)
        throws CannotCompileException
    {
        declaringClass.checkModify();
        ConstPool pool = methodInfo.getConstPool();
        CodeAttribute ca = methodInfo.getCodeAttribute();
        if (ca == null)
            throw new CannotCompileException("no method body");

        CodeIterator iterator = ca.iterator();
        int retAddr = ca.getMaxLocals();
        Bytecode b = new Bytecode(pool, 0, retAddr + 1);
        b.setStackDepth(ca.getMaxStack() + 1);
        Javac jv = new Javac(b, declaringClass);
        try {
            int nvars = jv.recordParams(getParameterTypes(),
                                        Modifier.isStatic(getModifiers()));
            jv.recordParamNames(ca, nvars);
            CtClass rtype = getReturnType0();
            int varNo = jv.recordReturnType(rtype, true);
            jv.recordLocalVariables(ca, 0);

            int handlerLen = insertAfterHandler(asFinally, b, rtype, varNo);

            byte[] save = makeSaveCode(pool, rtype, varNo);
            byte[] restore = makeRestoreCode(b, pool, rtype, varNo);

            b.addAstore(retAddr);
            jv.compileStmnt(src);
            b.addRet(retAddr);
            ca.setMaxStack(b.getMaxStack());
            ca.setMaxLocals(b.getMaxLocals());

            int gapPos = iterator.append(b.get());
            iterator.append(b.getExceptionTable(), gapPos);

            if (asFinally)
                ca.getExceptionTable().add(0, gapPos, gapPos, 0);

            int gapLen = iterator.getCodeLength() - gapPos - handlerLen;
            int subr = iterator.getCodeLength() - gapLen;

            while (iterator.hasNext()) {
                int pos = iterator.next();
                if (pos >= subr)
                    break;

                int c = iterator.byteAt(pos);
                if (c == Opcode.ARETURN || c == Opcode.IRETURN
                    || c == Opcode.FRETURN || c == Opcode.LRETURN
                    || c == Opcode.DRETURN || c == Opcode.RETURN) {
                    insertJSR(iterator, subr, pos, save, restore);
                    subr = iterator.getCodeLength() - gapLen;
                }
            }