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Hi Trevor, I think ClassFile.of is good for this particular purpose. There is nothing in the header parsing that the default class file handling options is not suitable for.</div>
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-Chen</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> core-libs-dev <core-libs-dev-retn@openjdk.org> on behalf of Trevor Bond <trevorkbond@gmail.com><br>
<b>Sent:</b> Wednesday, November 5, 2025 9:56 PM<br>
<b>To:</b> core-libs-dev@openjdk.org <core-libs-dev@openjdk.org><br>
<b>Subject:</b> Questions regarding JDK-8350938 (ResourceParsingClassHierarchyResolver)</font>
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all,</span>
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I'm new to contributing to OpenJDK and have been working with Dan Smith as a mentor. I've been looking at JDK-8350938, which suggests refactoring ResourceParsingClassHierarchyResolver to avoid inflating all UTF8 constant pool entries by using ClassReaderImpl.
ClassReaderImpl stores constant pool offsets and later lazily reads/inflates UTF8 entries as needed, so it seems to make sense to use here as a performance enhancement.</div>
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I have an initial prototype that removes manual parsing in getClassInfo() and instead constructs a ClassReaderImpl and uses its helper methods to return the needed class information.<br>
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One question before I try to move forward with contributing: </div>
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- ClassReaderImpl takes a ClassFile context. I used ClassFile.of() (a ClassFile context with default options). Is this the correct usage here, or should the resolver provide a more specific context?</div>
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I am also open to and would appreciate any other ideas or feedback on this implementation.</div>
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I’ve included the small patch below for reference. </div>
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Thanks for your help,</div>
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Trevor<br>
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diff --git a/src/java.base/share/classes/jdk/internal/classfile/impl/ClassHierarchyImpl.java b/src/java.base/share/classes/jdk/internal/classfile/impl/ClassHierarchyImpl.java<br>
index 5be14f42baa..463845ce612 100644<br>
--- a/src/java.base/share/classes/jdk/internal/classfile/impl/ClassHierarchyImpl.java<br>
+++ b/src/java.base/share/classes/jdk/internal/classfile/impl/ClassHierarchyImpl.java<br>
@@ -30,7 +30,10 @@<br>
import java.io.IOException;<br>
import java.io.InputStream;<br>
import java.io.UncheckedIOException;<br>
+import java.lang.classfile.ClassFile;<br>
import java.lang.classfile.ClassHierarchyResolver;<br>
+import java.lang.classfile.ClassReader;<br>
+import java.lang.classfile.constantpool.ClassEntry;<br>
import java.lang.constant.ClassDesc;<br>
import java.util.Collection;<br>
import java.util.HashMap;<br>
@@ -164,31 +167,12 @@ public ResourceParsingClassHierarchyResolver(Function<ClassDesc, InputStream> cl<br>
public ClassHierarchyResolver.ClassHierarchyInfo getClassInfo(ClassDesc classDesc) {<br>
var ci = streamProvider.apply(classDesc);<br>
if (ci == null) return null;<br>
- try (var in = new DataInputStream(new BufferedInputStream(ci))) {<br>
- in.skipBytes(8);<br>
- int cpLength = in.readUnsignedShort();<br>
- String[] cpStrings = new String[cpLength];<br>
- int[] cpClasses = new int[cpLength];<br>
- for (int i = 1; i < cpLength; i++) {<br>
- int tag;<br>
- switch (tag = in.readUnsignedByte()) {<br>
- case TAG_UTF8 -> cpStrings[i] = in.readUTF();<br>
- case TAG_CLASS -> cpClasses[i] = in.readUnsignedShort();<br>
- case TAG_STRING, TAG_METHOD_TYPE, TAG_MODULE, TAG_PACKAGE -> in.skipBytes(2);<br>
- case TAG_METHOD_HANDLE -> in.skipBytes(3);<br>
- case TAG_INTEGER, TAG_FLOAT, TAG_FIELDREF, TAG_METHODREF, TAG_INTERFACE_METHODREF,<br>
- TAG_NAME_AND_TYPE, TAG_DYNAMIC, TAG_INVOKE_DYNAMIC -> in.skipBytes(4);<br>
- case TAG_LONG, TAG_DOUBLE -> {<br>
- in.skipBytes(8);<br>
- i++;<br>
- }<br>
- default -> throw new IllegalStateException("Bad tag (" + tag + ") at index (" + i + ")");<br>
- }<br>
- }<br>
- boolean isInterface = (in.readUnsignedShort() & ACC_INTERFACE) != 0;<br>
- in.skipBytes(2);<br>
- int superIndex = in.readUnsignedShort();<br>
- var superClass = superIndex > 0 ? ClassDesc.ofInternalName(cpStrings[cpClasses[superIndex]]) : null;<br>
+ try (ci) {<br>
+ ClassReader reader = new ClassReaderImpl(ci.readAllBytes(), (ClassFileImpl) ClassFile.of());<br>
+ boolean isInterface = (reader.flags() & ACC_INTERFACE) != 0;<br>
+ ClassDesc superClass = reader.superclassEntry()<br>
+ .map(ClassEntry::asSymbol)<br>
+ .orElse(null);<br>
return new ClassHierarchyInfoImpl(superClass, isInterface);<br>
} catch (IOException ioe) {<br>
throw new UncheckedIOException(ioe);</div>
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