Class File API

JEP 457 Class-File API is a preview API to provide a standard API for parsing, generating, and transforming Java class files.

This repository demonstrates how to create a class that has a field, invokes a method, and prints a message, and also how to parse it with the said API.

Generating

class-file-api/src/main/java/org/jugistanbul/GenerateClass.java

Lines 20 to 35 in 62e2120

	var className = Info.CLASS_NAME.getClassName();
	ClassFile.of().buildTo(Path.of(STR."\{className}.class"), of(className),
	classBuilder -> classBuilder
	.withField("myField", of("java.lang.String"), ACC_PRIVATE)
	.withMethodBody("hello", MethodTypeDesc.of(CD_void), ACC_STATIC,
	codeBuilder -> codeBuilder
	.getstatic(of("java.lang.System"), "out", of("java.io.PrintStream"))
	.ldc("Hello, this class is generated by Class-File API which is a preview API to provide a standard API for parsing, generating, and transforming Java class files.")
	.invokevirtual(of("java.io.PrintStream"), "println",
	MethodTypeDesc.of(CD_void, of("java.lang.Object")))
	.return_())
	.withMethodBody("main", MethodTypeDesc.of(CD_void, of("java.lang.String").arrayType()), ACC_PUBLIC | ACC_STATIC,
	codeBuilder -> codeBuilder
	.invokeInstruction(Opcode.INVOKESTATIC, of(className), "hello", MethodTypeDesc.of(CD_void), false)
	.return_()));
	}

Parsing

class-file-api/src/main/java/org/jugistanbul/ParseClass.java

Lines 18 to 26 in f603f59

	var classModel = ClassFile.of().parse(getGivenClassBytes(Info.CLASS_NAME.getClassName()));
	for (var classElement : classModel) {
	switch (classElement) {
	case MethodModel mm -> System.out.printf("Method name %s type %s%n", mm.methodName().stringValue(), mm.methodType().stringValue());
	case FieldModel fm -> System.out.printf("Field name %s type %s%n", fm.fieldName().stringValue(), fm.fieldType().stringValue());
	default -> {
	}
	}
	}

Build and run

sh run.sh