Method to detect a byte array is a valid XLSX data or not

pom.xml

<dependencies>
	<!--https://mvnrepository.com/artifact/org.apache.commons/commons-lang3-->
	<dependency>
		<groupId>org.apache.commons</groupId>
		<artifactId>commons-lang3</artifactId>
		<version>3.20.0</version>
	</dependency>
	<!--https://mvnrepository.com/artifact/org.zeroturnaround/zt-zip-->
	<dependency>
		<groupId>org.zeroturnaround</groupId>
		<artifactId>zt-zip</artifactId>
		<version>1.17</version>
	</dependency>
</dependencies>

XlsxUtil.java

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Base64;
import java.util.Base64.Decoder;
import java.util.Objects;
import java.util.function.Predicate;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.apache.commons.lang3.function.FailableFunction;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
import org.zeroturnaround.zip.ZipUtil;

public class XlsxUtil {

	public static void main(final String[] args) throws IOException, SAXException, ParserConfigurationException {
		//
		System.out.println(isXlsx(null));
		//
		System.out.println(isXlsx(new byte[] {}));
		//
		System.out.println(isXlsx(new byte[] { 0 }));
		//
		System.out.println(isXlsx(new byte[] { 0, 0 }));
		//
		final Decoder decoder = Base64.getDecoder();
		//
		System.out.println(isXlsx(decoder != null ? decoder.decode(
				"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")
				: null));
		//
	}

	public static boolean isXlsx(final byte[] bs) throws IOException, SAXException, ParserConfigurationException {
		//
		boolean contentTypeXmlFound = false;
		//
		try (final InputStream is = testAndApply(Objects::nonNull, bs, ByteArrayInputStream::new, null);
				final ZipInputStream zis = testAndApply(Objects::nonNull, is, ZipInputStream::new, null)) {
			//
			ZipEntry ze = null;
			//
			while ((ze = getNextEntry(zis)) != null) {
				//
				if (contentTypeXmlFound = Objects.equals("[Content_Types].xml", ze.getName())) {
					//
					break;
					//
				} // if
					//
			} // while
				//
		} // try
			//
		boolean isXlsx = false;
		//
		if (contentTypeXmlFound) {
			//
			try (final InputStream is = testAndApply(Objects::nonNull, bs, ByteArrayInputStream::new, null)) {
				//
				try (final InputStream bais = testAndApply(x -> x != null && x.length > 0,
						ZipUtil.unpackEntry(is, "[Content_Types].xml"), ByteArrayInputStream::new, null)) {
					//
					final NodeList childNodes = getChildNodes(getDocumentElement(
							bais != null ? parse(newDocumentBuilder(DocumentBuilderFactory.newDefaultInstance()), bais)
									: null));
					//
					for (int i = 0; i < getLength(childNodes); i++) {
						//
						if (Objects.equals("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml",
								getTextContent(getNamedItem(getAttributes(item(childNodes, i)), "ContentType")))
								&& (isXlsx = true)) {
							//
							break;
							//
						} // if
							//
					} // for
						//
				} // try
					//
			} // try
				//
		} // if
			//
		return isXlsx;
		//
	}

	private static ZipEntry getNextEntry(final ZipInputStream instance) {
		//
		Object obj = null;
		//
		try {
			//
			final Method method = ZipInputStream.class.getDeclaredMethod("getNextEntry");
			//
			obj = Boolean.logicalOr(isStatic(method), instance != null) ? invoke(method, instance) : null;
			//
		} catch (final NoSuchMethodException | IllegalAccessException e) {
			//
			throw new RuntimeException(e);
			//
		} catch (final InvocationTargetException e) {
			//
			final Throwable targetException = e.getTargetException();
			//
			throw targetException instanceof RuntimeException re ? re : new RuntimeException(targetException);
			//
		} // try
			//
		return obj instanceof ZipEntry ze ? ze : null;
		//
	}

	private static <T, R, E extends Throwable> R testAndApply(final Predicate<T> predicate, final T value,
			final FailableFunction<T, R, E> functionTrue, final FailableFunction<T, R, E> functionFalse) throws E {
		return test(predicate, value) ? apply(functionTrue, value) : apply(functionFalse, value);
	}

	private static <T, R, E extends Throwable> R apply(final FailableFunction<T, R, E> instance, final T value)
			throws E {
		return instance != null ? instance.apply(value) : null;
	}

	private static <T> boolean test(final Predicate<T> instance, final T value) {
		return instance != null && instance.test(value);
	}

	private static boolean isStatic(final Member instance) {
		return instance != null && Modifier.isStatic(instance.getModifiers());
	}

	private static Object invoke(final Method method, final Object instance, final Object... args)
			throws IllegalAccessException, InvocationTargetException {
		return method != null ? method.invoke(instance, args) : null;
	}

	private static DocumentBuilder newDocumentBuilder(final DocumentBuilderFactory instance)
			throws ParserConfigurationException {
		return instance != null ? instance.newDocumentBuilder() : null;
	}

	private static Document parse(final DocumentBuilder instance, final InputStream is)
			throws SAXException, IOException {
		return instance != null ? instance.parse(is) : null;
	}

	private static Element getDocumentElement(final Document instance) {
		return instance != null ? instance.getDocumentElement() : null;
	}

	private static NodeList getChildNodes(final Node instance) {
		return instance != null ? instance.getChildNodes() : null;
	}

	private static int getLength(final NodeList instance) {
		return instance != null ? instance.getLength() : 0;
	}

	private static Node item(final NodeList instance, final int index) {
		return instance != null ? instance.item(index) : null;
	}

	private static NamedNodeMap getAttributes(final Node instance) {
		return instance != null ? instance.getAttributes() : null;
	}

	private static Node getNamedItem(final NamedNodeMap instance, final String name) {
		return instance != null ? instance.getNamedItem(name) : null;
	}

	private static String getTextContent(final Node instance) {
		return instance != null ? instance.getTextContent() : null;
	}

}

https://en.wikipedia.org/wiki/Open_Packaging_Conventions#Package,_parts,_and_relationships