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Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation
simple. It is a class library for editing bytecodes in Java.
/*
* Javassist, a Java-bytecode translator toolkit.
* Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. Alternatively, the contents of this file may be used under
* the terms of the GNU Lesser General Public License Version 2.1 or later,
* or the Apache License Version 2.0.
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*/
package javassist.bytecode;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
/**
* field_info structure.
*
* The following code adds a public field width
* of int type:
*
* ClassFile cf = ...
* FieldInfo f = new FieldInfo(cf.getConstPool(), "width", "I");
* f.setAccessFlags(AccessFlag.PUBLIC);
* cf.addField(f);
*
*
* @see javassist.CtField#getFieldInfo()
*/
public final class FieldInfo {
ConstPool constPool;
int accessFlags;
int name;
String cachedName;
String cachedType;
int descriptor;
List attribute; // may be null.
private FieldInfo(ConstPool cp) {
constPool = cp;
accessFlags = 0;
attribute = null;
}
/**
* Constructs a field_info structure.
*
* @param cp a constant pool table
* @param fieldName field name
* @param desc field descriptor
*
* @see Descriptor
*/
public FieldInfo(ConstPool cp, String fieldName, String desc) {
this(cp);
name = cp.addUtf8Info(fieldName);
cachedName = fieldName;
descriptor = cp.addUtf8Info(desc);
}
FieldInfo(ConstPool cp, DataInputStream in) throws IOException {
this(cp);
read(in);
}
/**
* Returns a string representation of the object.
*/
@Override
public String toString() {
return getName() + " " + getDescriptor();
}
/**
* Copies all constant pool items to a given new constant pool
* and replaces the original items with the new ones.
* This is used for garbage collecting the items of removed fields
* and methods.
*
* @param cp the destination
*/
void compact(ConstPool cp) {
name = cp.addUtf8Info(getName());
descriptor = cp.addUtf8Info(getDescriptor());
attribute = AttributeInfo.copyAll(attribute, cp);
constPool = cp;
}
void prune(ConstPool cp) {
List newAttributes = new ArrayList();
AttributeInfo invisibleAnnotations
= getAttribute(AnnotationsAttribute.invisibleTag);
if (invisibleAnnotations != null) {
invisibleAnnotations = invisibleAnnotations.copy(cp, null);
newAttributes.add(invisibleAnnotations);
}
AttributeInfo visibleAnnotations
= getAttribute(AnnotationsAttribute.visibleTag);
if (visibleAnnotations != null) {
visibleAnnotations = visibleAnnotations.copy(cp, null);
newAttributes.add(visibleAnnotations);
}
AttributeInfo signature
= getAttribute(SignatureAttribute.tag);
if (signature != null) {
signature = signature.copy(cp, null);
newAttributes.add(signature);
}
int index = getConstantValue();
if (index != 0) {
index = constPool.copy(index, cp, null);
newAttributes.add(new ConstantAttribute(cp, index));
}
attribute = newAttributes;
name = cp.addUtf8Info(getName());
descriptor = cp.addUtf8Info(getDescriptor());
constPool = cp;
}
/**
* Returns the constant pool table used
* by this field_info.
*/
public ConstPool getConstPool() {
return constPool;
}
/**
* Returns the field name.
*/
public String getName() {
if (cachedName == null)
cachedName = constPool.getUtf8Info(name);
return cachedName;
}
/**
* Sets the field name.
*/
public void setName(String newName) {
name = constPool.addUtf8Info(newName);
cachedName = newName;
}
/**
* Returns the access flags.
*
* @see AccessFlag
*/
public int getAccessFlags() {
return accessFlags;
}
/**
* Sets the access flags.
*
* @see AccessFlag
*/
public void setAccessFlags(int acc) {
accessFlags = acc;
}
/**
* Returns the field descriptor.
*
* @see Descriptor
*/
public String getDescriptor() {
return constPool.getUtf8Info(descriptor);
}
/**
* Sets the field descriptor.
*
* @see Descriptor
*/
public void setDescriptor(String desc) {
if (!desc.equals(getDescriptor()))
descriptor = constPool.addUtf8Info(desc);
}
/**
* Finds a ConstantValue attribute and returns the index into
* the constant_pool table.
*
* @return 0 if a ConstantValue attribute is not found.
*/
public int getConstantValue() {
if ((accessFlags & AccessFlag.STATIC) == 0)
return 0;
ConstantAttribute attr
= (ConstantAttribute)getAttribute(ConstantAttribute.tag);
if (attr == null)
return 0;
return attr.getConstantValue();
}
/**
* Returns all the attributes. The returned List object
* is shared with this object. If you add a new attribute to the list,
* the attribute is also added to the field represented by this
* object. If you remove an attribute from the list, it is also removed
* from the field.
*
* @return a list of AttributeInfo objects.
* @see AttributeInfo
*/
public List getAttributes() {
if (attribute == null)
attribute = new ArrayList();
return attribute;
}
/**
* Returns the attribute with the specified name.
* It returns null if the specified attribute is not found.
*
* An attribute name can be obtained by, for example,
* {@link AnnotationsAttribute#visibleTag} or
* {@link AnnotationsAttribute#invisibleTag}.
*
*
* @param name attribute name
* @see #getAttributes()
*/
public AttributeInfo getAttribute(String name) {
return AttributeInfo.lookup(attribute, name);
}
/**
* Removes an attribute with the specified name.
*
* @param name attribute name.
* @return the removed attribute or null.
* @since 3.21
*/
public AttributeInfo removeAttribute(String name) {
return AttributeInfo.remove(attribute, name);
}
/**
* Appends an attribute. If there is already an attribute with
* the same name, the new one substitutes for it.
*
* @see #getAttributes()
*/
public void addAttribute(AttributeInfo info) {
if (attribute == null)
attribute = new ArrayList();
AttributeInfo.remove(attribute, info.getName());
attribute.add(info);
}
private void read(DataInputStream in) throws IOException {
accessFlags = in.readUnsignedShort();
name = in.readUnsignedShort();
descriptor = in.readUnsignedShort();
int n = in.readUnsignedShort();
attribute = new ArrayList();
for (int i = 0; i < n; ++i)
attribute.add(AttributeInfo.read(constPool, in));
}
void write(DataOutputStream out) throws IOException {
out.writeShort(accessFlags);
out.writeShort(name);
out.writeShort(descriptor);
if (attribute == null)
out.writeShort(0);
else {
out.writeShort(attribute.size());
AttributeInfo.writeAll(attribute, out);
}
}
}