classreader.java

asm的源码包 并且包含英文的文档

                // case ClassWriter.STR:
                // case ClassWriter.CLASS:
                default:
                    item.set(tag, readUTF8(index, buf), null, null);
                    break;
            }

            int index2 = item.hashCode % items2.length;
            item.next = items2[index2];
            items2[index2] = item;
        }

        int off = items[1] - 1;
        classWriter.pool.putByteArray(b, off, header - off);
        classWriter.items = items2;
        classWriter.threshold = (int) (0.75d * ll);
        classWriter.index = ll;
    }

    /**
     * Constructs a new {@link ClassReader} object.
     * 
     * @param is an input stream from which to read the class.
     * @throws IOException if a problem occurs during reading.
     */
    public ClassReader(final InputStream is) throws IOException {
        this(readClass(is));
    }

    /**
     * Constructs a new {@link ClassReader} object.
     * 
     * @param name the fully qualified name of the class to be read.
     * @throws IOException if an exception occurs during reading.
     */
    public ClassReader(final String name) throws IOException {
        this(ClassLoader.getSystemResourceAsStream(name.replace('.', '/')
                + ".class"));
    }

    /**
     * Reads the bytecode of a class.
     * 
     * @param is an input stream from which to read the class.
     * @return the bytecode read from the given input stream.
     * @throws IOException if a problem occurs during reading.
     */
    private static byte[] readClass(final InputStream is) throws IOException {
        if (is == null) {
            throw new IOException("Class not found");
        }
        byte[] b = new byte[is.available()];
        int len = 0;
        while (true) {
            int n = is.read(b, len, b.length - len);
            if (n == -1) {
                if (len < b.length) {
                    byte[] c = new byte[len];
                    System.arraycopy(b, 0, c, 0, len);
                    b = c;
                }
                return b;
            }
            len += n;
            if (len == b.length) {
                byte[] c = new byte[b.length + 1000];
                System.arraycopy(b, 0, c, 0, len);
                b = c;
            }
        }
    }

    // ------------------------------------------------------------------------
    // Public methods
    // ------------------------------------------------------------------------

    /**
     * Makes the given visitor visit the Java class of this {@link ClassReader}.
     * This class is the one specified in the constructor (see
     * {@link #ClassReader(byte[]) ClassReader}).
     * 
     * @param classVisitor the visitor that must visit this class.
     * @param flags option flags that can be used to modify the default behavior
     *        of this class. See {@link #SKIP_DEBUG}, {@link #EXPAND_FRAMES}.
     */
    public void accept(final ClassVisitor classVisitor, final int flags) {
        accept(classVisitor, new Attribute[0], flags);
    }

    /**
     * Makes the given visitor visit the Java class of this {@link ClassReader}.
     * This class is the one specified in the constructor (see
     * {@link #ClassReader(byte[]) ClassReader}).
     * 
     * @param classVisitor the visitor that must visit this class.
     * @param attrs prototypes of the attributes that must be parsed during the
     *        visit of the class. Any attribute whose type is not equal to the
     *        type of one the prototypes will not be parsed: its byte array
     *        value will be passed unchanged to the ClassWriter. <i>This may
     *        corrupt it if this value contains references to the constant pool,
     *        or has syntactic or semantic links with a class element that has
     *        been transformed by a class adapter between the reader and the
     *        writer</i>.
     * @param flags option flags that can be used to modify the default behavior
     *        of this class. See {@link #SKIP_DEBUG}, {@link #EXPAND_FRAMES}.
     */
    public void accept(
        final ClassVisitor classVisitor,
        final Attribute[] attrs,
        final int flags)
    {
        byte[] b = this.b; // the bytecode array
        char[] c = new char[maxStringLength]; // buffer used to read strings
        int i, j, k; // loop variables
        int u, v, w; // indexes in b
        Attribute attr;

        int access;
        String name;
        String desc;
        String attrName;
        String signature;
        int anns = 0;
        int ianns = 0;
        Attribute cattrs = null;

        // visits the header
        u = header;
        access = readUnsignedShort(u);
        name = readClass(u + 2, c);
        v = items[readUnsignedShort(u + 4)];
        String superClassName = v == 0 ? null : readUTF8(v, c);
        String[] implementedItfs = new String[readUnsignedShort(u + 6)];
        w = 0;
        u += 8;
        for (i = 0; i < implementedItfs.length; ++i) {
            implementedItfs[i] = readClass(u, c);
            u += 2;
        }

        boolean skipCode = (flags & SKIP_CODE) != 0;
        boolean skipDebug = (flags & SKIP_DEBUG) != 0;
        boolean unzip = (flags & EXPAND_FRAMES) != 0;

        // skips fields and methods
        v = u;
        i = readUnsignedShort(v);
        v += 2;
        for (; i > 0; --i) {
            j = readUnsignedShort(v + 6);
            v += 8;
            for (; j > 0; --j) {
                v += 6 + readInt(v + 2);
            }
        }
        i = readUnsignedShort(v);
        v += 2;
        for (; i > 0; --i) {
            j = readUnsignedShort(v + 6);
            v += 8;
            for (; j > 0; --j) {
                v += 6 + readInt(v + 2);
            }
        }
        // reads the class's attributes
        signature = null;
        String sourceFile = null;
        String sourceDebug = null;
        String enclosingOwner = null;
        String enclosingName = null;
        String enclosingDesc = null;

        i = readUnsignedShort(v);
        v += 2;
        for (; i > 0; --i) {
            attrName = readUTF8(v, c);
            // tests are sorted in decreasing frequency order
            // (based on frequencies observed on typical classes)
            if (attrName.equals("SourceFile")) {
                sourceFile = readUTF8(v + 6, c);
            } else if (attrName.equals("InnerClasses")) {
                w = v + 6;
            } else if (attrName.equals("EnclosingMethod")) {
                enclosingOwner = readClass(v + 6, c);
                int item = readUnsignedShort(v + 8);
                if (item != 0) {
                    enclosingName = readUTF8(items[item], c);
                    enclosingDesc = readUTF8(items[item] + 2, c);
                }
            } else if (attrName.equals("Signature")) {
                signature = readUTF8(v + 6, c);
            } else if (attrName.equals("RuntimeVisibleAnnotations")) {
                anns = v + 6;
            } else if (attrName.equals("Deprecated")) {
                access |= Opcodes.ACC_DEPRECATED;
            } else if (attrName.equals("Synthetic")) {
                access |= Opcodes.ACC_SYNTHETIC;
            } else if (attrName.equals("SourceDebugExtension")) {
                int len = readInt(v + 2);
                sourceDebug = readUTF(v + 6, len, new char[len]);
            } else if (attrName.equals("RuntimeInvisibleAnnotations")) {
                ianns = v + 6;
            } else {
                attr = readAttribute(attrs,
                        attrName,
                        v + 6,
                        readInt(v + 2),
                        c,
                        -1,
                        null);
                if (attr != null) {
                    attr.next = cattrs;
                    cattrs = attr;
                }
            }
            v += 6 + readInt(v + 2);
        }
        // calls the visit method
        classVisitor.visit(readInt(4),
                access,
                name,
                signature,
                superClassName,
                implementedItfs);

        // calls the visitSource method
        if (!skipDebug && (sourceFile != null || sourceDebug != null)) {
            classVisitor.visitSource(sourceFile, sourceDebug);
        }

        // calls the visitOuterClass method
        if (enclosingOwner != null) {
            classVisitor.visitOuterClass(enclosingOwner,
                    enclosingName,
                    enclosingDesc);
        }

        // visits the class annotations
        for (i = 1; i >= 0; --i) {
            v = i == 0 ? ianns : anns;
            if (v != 0) {
                j = readUnsignedShort(v);
                v += 2;
                for (; j > 0; --j) {
                    v = readAnnotationValues(v + 2,
                            c,
                            true,
                            classVisitor.visitAnnotation(readUTF8(v, c), i != 0));
                }
            }
        }

        // visits the class attributes
        while (cattrs != null) {
            attr = cattrs.next;
            cattrs.next = null;
            classVisitor.visitAttribute(cattrs);
            cattrs = attr;
        }

        // calls the visitInnerClass method
        if (w != 0) {
            i = readUnsignedShort(w);
            w += 2;
            for (; i > 0; --i) {
                classVisitor.visitInnerClass(readUnsignedShort(w) == 0
                        ? null
                        : readClass(w, c), readUnsignedShort(w + 2) == 0
                        ? null
                        : readClass(w + 2, c), readUnsignedShort(w + 4) == 0
                        ? null
                        : readUTF8(w + 4, c), readUnsignedShort(w + 6));
                w += 8;
            }
        }

        // visits the fields
        i = readUnsignedShort(u);
        u += 2;
        for (; i > 0; --i) {
            access = readUnsignedShort(u);
            name = readUTF8(u + 2, c);
            desc = readUTF8(u + 4, c);
            // visits the field's attributes and looks for a ConstantValue
            // attribute
            int fieldValueItem = 0;
            signature = null;
            anns = 0;
            ianns = 0;
            cattrs = null;

            j = readUnsignedShort(u + 6);
            u += 8;
            for (; j > 0; --j) {
                attrName = readUTF8(u, c);
                // tests are sorted in decreasing frequency order
                // (based on frequencies observed on typical classes)
                if (attrName.equals("ConstantValue")) {
                    fieldValueItem = readUnsignedShort(u + 6);
                } else if (attrName.equals("Signature")) {
                    signature = readUTF8(u + 6, c);
                } else if (attrName.equals("Deprecated")) {
                    access |= Opcodes.ACC_DEPRECATED;
                } else if (attrName.equals("Synthetic")) {
                    access |= Opcodes.ACC_SYNTHETIC;