Java example source code file (Attribute.java)

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Java - Java tags/keywords

attribute, bytevector, classreader, classwriter, label, string

The Attribute.java Java example source code

/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2011 INRIA, France Telecom
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
package clojure.asm;

/**
 * A non standard class, field, method or code attribute.
 *
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {

    /**
     * The type of this attribute.
     */
    public final String type;

    /**
     * The raw value of this attribute, used only for unknown attributes.
     */
    byte[] value;

    /**
     * The next attribute in this attribute list. May be <tt>null.
     */
    Attribute next;

    /**
     * Constructs a new empty attribute.
     *
     * @param type
     *            the type of the attribute.
     */
    protected Attribute(final String type) {
        this.type = type;
    }

    /**
     * Returns <tt>true if this type of attribute is unknown. The default
     * implementation of this method always returns <tt>true.
     *
     * @return <tt>true if this type of attribute is unknown.
     */
    public boolean isUnknown() {
        return true;
    }

    /**
     * Returns <tt>true if this type of attribute is a code attribute.
     *
     * @return <tt>true if this type of attribute is a code attribute.
     */
    public boolean isCodeAttribute() {
        return false;
    }

    /**
     * Returns the labels corresponding to this attribute.
     *
     * @return the labels corresponding to this attribute, or <tt>null if
     *         this attribute is not a code attribute that contains labels.
     */
    protected Label[] getLabels() {
        return null;
    }

    /**
     * Reads a {@link #type type} attribute. This method must return a
     * <i>new {@link Attribute} object, of type {@link #type type},
     * corresponding to the <tt>len bytes starting at the given offset, in
     * the given class reader.
     *
     * @param cr
     *            the class that contains the attribute to be read.
     * @param off
     *            index of the first byte of the attribute's content in
     *            {@link ClassReader#b cr.b}. The 6 attribute header bytes,
     *            containing the type and the length of the attribute, are not
     *            taken into account here.
     * @param len
     *            the length of the attribute's content.
     * @param buf
     *            buffer to be used to call {@link ClassReader#readUTF8
     *            readUTF8}, {@link ClassReader#readClass(int,char[]) readClass}
     *            or {@link ClassReader#readConst readConst}.
     * @param codeOff
     *            index of the first byte of code's attribute content in
     *            {@link ClassReader#b cr.b}, or -1 if the attribute to be read
     *            is not a code attribute. The 6 attribute header bytes,
     *            containing the type and the length of the attribute, are not
     *            taken into account here.
     * @param labels
     *            the labels of the method's code, or <tt>null if the
     *            attribute to be read is not a code attribute.
     * @return a <i>new {@link Attribute} object corresponding to the given
     *         bytes.
     */
    protected Attribute read(final ClassReader cr, final int off,
            final int len, final char[] buf, final int codeOff,
            final Label[] labels) {
        Attribute attr = new Attribute(type);
        attr.value = new byte[len];
        System.arraycopy(cr.b, off, attr.value, 0, len);
        return attr;
    }

    /**
     * Returns the byte array form of this attribute.
     *
     * @param cw
     *            the class to which this attribute must be added. This
     *            parameter can be used to add to the constant pool of this
     *            class the items that corresponds to this attribute.
     * @param code
     *            the bytecode of the method corresponding to this code
     *            attribute, or <tt>null if this attribute is not a code
     *            attributes.
     * @param len
     *            the length of the bytecode of the method corresponding to this
     *            code attribute, or <tt>null if this attribute is not a
     *            code attribute.
     * @param maxStack
     *            the maximum stack size of the method corresponding to this
     *            code attribute, or -1 if this attribute is not a code
     *            attribute.
     * @param maxLocals
     *            the maximum number of local variables of the method
     *            corresponding to this code attribute, or -1 if this attribute
     *            is not a code attribute.
     * @return the byte array form of this attribute.
     */
    protected ByteVector write(final ClassWriter cw, final byte[] code,
            final int len, final int maxStack, final int maxLocals) {
        ByteVector v = new ByteVector();
        v.data = value;
        v.length = value.length;
        return v;
    }

    /**
     * Returns the length of the attribute list that begins with this attribute.
     *
     * @return the length of the attribute list that begins with this attribute.
     */
    final int getCount() {
        int count = 0;
        Attribute attr = this;
        while (attr != null) {
            count += 1;
            attr = attr.next;
        }
        return count;
    }

    /**
     * Returns the size of all the attributes in this attribute list.
     *
     * @param cw
     *            the class writer to be used to convert the attributes into
     *            byte arrays, with the {@link #write write} method.
     * @param code
     *            the bytecode of the method corresponding to these code
     *            attributes, or <tt>null if these attributes are not code
     *            attributes.
     * @param len
     *            the length of the bytecode of the method corresponding to
     *            these code attributes, or <tt>null if these attributes
     *            are not code attributes.
     * @param maxStack
     *            the maximum stack size of the method corresponding to these
     *            code attributes, or -1 if these attributes are not code
     *            attributes.
     * @param maxLocals
     *            the maximum number of local variables of the method
     *            corresponding to these code attributes, or -1 if these
     *            attributes are not code attributes.
     * @return the size of all the attributes in this attribute list. This size
     *         includes the size of the attribute headers.
     */
    final int getSize(final ClassWriter cw, final byte[] code, final int len,
            final int maxStack, final int maxLocals) {
        Attribute attr = this;
        int size = 0;
        while (attr != null) {
            cw.newUTF8(attr.type);
            size += attr.write(cw, code, len, maxStack, maxLocals).length + 6;
            attr = attr.next;
        }
        return size;
    }

    /**
     * Writes all the attributes of this attribute list in the given byte
     * vector.
     *
     * @param cw
     *            the class writer to be used to convert the attributes into
     *            byte arrays, with the {@link #write write} method.
     * @param code
     *            the bytecode of the method corresponding to these code
     *            attributes, or <tt>null if these attributes are not code
     *            attributes.
     * @param len
     *            the length of the bytecode of the method corresponding to
     *            these code attributes, or <tt>null if these attributes
     *            are not code attributes.
     * @param maxStack
     *            the maximum stack size of the method corresponding to these
     *            code attributes, or -1 if these attributes are not code
     *            attributes.
     * @param maxLocals
     *            the maximum number of local variables of the method
     *            corresponding to these code attributes, or -1 if these
     *            attributes are not code attributes.
     * @param out
     *            where the attributes must be written.
     */
    final void put(final ClassWriter cw, final byte[] code, final int len,
            final int maxStack, final int maxLocals, final ByteVector out) {
        Attribute attr = this;
        while (attr != null) {
            ByteVector b = attr.write(cw, code, len, maxStack, maxLocals);
            out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
            out.putByteArray(b.data, 0, b.length);
            attr = attr.next;
        }
    }
}