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An unofficial backport of the JDK Classfile API to Java 17
/*
* Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package io.github.dmlloyd.classfile.impl;
import java.lang.constant.ConstantDescs;
import java.lang.constant.MethodTypeDesc;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Consumer;
import io.github.dmlloyd.classfile.ClassBuilder;
import io.github.dmlloyd.classfile.ClassElement;
import io.github.dmlloyd.classfile.ClassModel;
import io.github.dmlloyd.classfile.ClassFile;
import io.github.dmlloyd.classfile.CustomAttribute;
import io.github.dmlloyd.classfile.constantpool.ClassEntry;
import io.github.dmlloyd.classfile.FieldBuilder;
import io.github.dmlloyd.classfile.FieldModel;
import io.github.dmlloyd.classfile.FieldTransform;
import io.github.dmlloyd.classfile.MethodBuilder;
import io.github.dmlloyd.classfile.MethodModel;
import io.github.dmlloyd.classfile.MethodTransform;
import io.github.dmlloyd.classfile.constantpool.Utf8Entry;
public final class DirectClassBuilder
extends AbstractDirectBuilder
implements ClassBuilder {
final ClassEntry thisClassEntry;
private final List fields = new ArrayList<>();
private final List methods = new ArrayList<>();
private ClassEntry superclassEntry;
private List interfaceEntries;
private int majorVersion;
private int minorVersion;
private int flags;
private int sizeHint;
public DirectClassBuilder(SplitConstantPool constantPool,
ClassFileImpl context,
ClassEntry thisClass) {
super(constantPool, context);
this.thisClassEntry = AbstractPoolEntry.maybeClone(constantPool, thisClass);
this.flags = ClassFile.DEFAULT_CLASS_FLAGS;
this.superclassEntry = null;
this.interfaceEntries = Collections.emptyList();
this.majorVersion = ClassFile.latestMajorVersion();
this.minorVersion = ClassFile.latestMinorVersion();
}
@Override
public ClassBuilder with(ClassElement element) {
if (element instanceof AbstractElement ae) {
ae.writeTo(this);
} else {
writeAttribute((CustomAttribute) element);
}
return this;
}
@Override
public ClassBuilder withField(Utf8Entry name,
Utf8Entry descriptor,
Consumer handler) {
return withField(new DirectFieldBuilder(constantPool, context, name, descriptor, null)
.run(handler));
}
@Override
public ClassBuilder transformField(FieldModel field, FieldTransform transform) {
DirectFieldBuilder builder = new DirectFieldBuilder(constantPool, context, field.fieldName(),
field.fieldType(), field);
builder.transform(field, transform);
return withField(builder);
}
@Override
public ClassBuilder withMethod(Utf8Entry name,
Utf8Entry descriptor,
int flags,
Consumer handler) {
return withMethod(new DirectMethodBuilder(constantPool, context, name, descriptor, flags, null)
.run(handler));
}
@Override
public ClassBuilder withMethod(String name, MethodTypeDesc descriptor, int flags, Consumer handler) {
var method = new DirectMethodBuilder(constantPool, context, constantPool.utf8Entry(name), constantPool.utf8Entry(descriptor), flags, null);
method.mDesc = descriptor;
return withMethod(method.run(handler));
}
@Override
public ClassBuilder transformMethod(MethodModel method, MethodTransform transform) {
DirectMethodBuilder builder = new DirectMethodBuilder(constantPool, context, method.methodName(),
method.methodType(),
method.flags().flagsMask(),
method);
builder.transform(method, transform);
return withMethod(builder);
}
// internal / for use by elements
ClassBuilder withField(Util.Writable field) {
fields.add(field);
return this;
}
ClassBuilder withMethod(Util.Writable method) {
methods.add(method);
return this;
}
void setSuperclass(ClassEntry superclassEntry) {
this.superclassEntry = superclassEntry;
}
void setInterfaces(List interfaces) {
this.interfaceEntries = interfaces;
}
void setVersion(int major, int minor) {
this.majorVersion = major;
this.minorVersion = minor;
}
void setFlags(int flags) {
this.flags = flags;
}
public void setSizeHint(int sizeHint) {
this.sizeHint = sizeHint;
}
public byte[] build() {
// The logic of this is very carefully ordered. We want to avoid
// repeated buffer copyings, so we accumulate lists of writers which
// all get written later into the same buffer. But, writing can often
// trigger CP / BSM insertions, so we cannot run the CP writer or
// BSM writers until everything else is written.
// Do this early because it might trigger CP activity
ClassEntry superclass = superclassEntry;
if (superclass != null)
superclass = AbstractPoolEntry.maybeClone(constantPool, superclass);
else if ((flags & ClassFile.ACC_MODULE) == 0 && !"java/lang/Object".equals(thisClassEntry.asInternalName()))
superclass = constantPool.classEntry(ConstantDescs.CD_Object);
List ies = new ArrayList<>(interfaceEntries.size());
for (ClassEntry ce : interfaceEntries)
ies.add(AbstractPoolEntry.maybeClone(constantPool, ce));
// We maintain two writers, and then we join them at the end
int size = sizeHint == 0 ? 256 : sizeHint;
BufWriterImpl head = new BufWriterImpl(constantPool, context, size);
BufWriterImpl tail = new BufWriterImpl(constantPool, context, size, thisClassEntry, majorVersion);
// The tail consists of fields and methods, and attributes
// This should trigger all the CP/BSM mutation
Util.writeList(tail, fields);
Util.writeList(tail, methods);
int attributesOffset = tail.size();
attributes.writeTo(tail);
// Now we have to append the BSM, if there is one
boolean written = constantPool.writeBootstrapMethods(tail);
if (written) {
// Update attributes count
tail.patchInt(attributesOffset, 2, attributes.size() + 1);
}
// Now we can make the head
head.writeInt(ClassFile.MAGIC_NUMBER);
head.writeU2(minorVersion);
head.writeU2(majorVersion);
constantPool.writeTo(head);
head.writeU2(flags);
head.writeIndex(thisClassEntry);
head.writeIndexOrZero(superclass);
Util.writeListIndices(head, ies);
// Join head and tail into an exact-size buffer
byte[] result = new byte[head.size() + tail.size()];
head.copyTo(result, 0);
tail.copyTo(result, head.size());
return result;
}
}