Migrate to Java 21 and Refactor for Modern Java Syntax

[marevol]

This PR upgrades the project to Java 21 by updating the Maven build configuration and enhancing source code using modern Java syntax features, including pattern matching and enhanced switch expressions. The README has been significantly extended to reflect these changes, highlighting new features and Java 21 support. Additionally, CollectionsUtil has been extended to support Java 21’s SequencedCollection and SequencedMap interfaces.

[Copilot]

Pull Request Overview

This PR migrates the project from Java 17 to Java 21, modernizing the codebase with contemporary Java syntax and features. The upgrade leverages pattern matching, enhanced switch expressions, and sequenced collections to improve code readability and performance.

• Migrates build configuration and CI pipeline to Java 21
• Refactors legacy if-else chains and switch statements to use modern pattern matching and switch expressions
• Adds support for Java 21's SequencedCollection and SequencedMap interfaces in CollectionsUtil
• Updates project documentation to reflect Java 21 features and enhanced capabilities

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
pom.xml	Updates Maven compiler plugin to target Java 21 and bumps version to 0.7.0-SNAPSHOT
.github/workflows/maven.yml	Updates CI pipeline to use JDK 21 instead of JDK 17
JsonUtil.java	Replaces traditional switch statement with modern switch expression for JSON character escaping
GenericsUtil.java	Converts if-else chains to pattern matching switch expressions for type handling
StringConversionUtil.java	Modernizes type conversion logic and character mapping with switch expressions
LongConversionUtil.java	Refactors object-to-long conversion methods using pattern matching
IntegerConversionUtil.java	Updates object-to-integer conversion with modern switch syntax
BooleanConversionUtil.java	Simplifies boolean conversion logic with nested switch expressions
CollectionsUtil.java	Adds new utility methods supporting Java 21's sequenced collections
README.md	Comprehensive documentation update highlighting Java 21 features and modern capabilities

[Copilot]

[nitpick] Missing spaces around operators and braces. Should be formatted as 'if (value == null) { return null; }' to maintain consistent code style.

Suggested change

	if(value==null){return null;}
	if (value == null) { return null; }

[Copilot]

[nitpick] Multiple variable declarations on a single line with inconsistent spacing. Should be separated into individual lines with proper spacing for better readability.

Suggested change

	char c;final int len=value.length();final StringBuilder buf=new StringBuilder(len*2);
	char c;
	final int len = value.length();
	final StringBuilder buf = new StringBuilder(len * 2);

[Copilot]

Entire method logic compressed into a single line, making it extremely difficult to read and debug. This should be properly formatted with line breaks and spacing.

Suggested change

	for(int i=0;i<len;i++){c=value.charAt(i);String escaped=switch(c){case'\\','"'->"\\"+c;case'/'->"\\/";case'\b'->"\\b";case'\t'->"\\t";case'\n'->"\\n";case'\f'->"\\f";case'\r'->"\\r";default->c<' '?"\\u"+"0".repeat(4-Integer.toHexString(c).length())+Integer.toHexString(c):String.valueOf(c);};buf.append(escaped);}return buf.toString();
	for (int i = 0; i < len; i++) {
	c = value.charAt(i);
	String escaped = switch (c) {
	case '\\', '"' -> "\\" + c;
	case '/' -> "\\/";
	case '\b' -> "\\b";
	case '\t' -> "\\t";
	case '\n' -> "\\n";
	case '\f' -> "\\f";
	case '\r' -> "\\r";
	default -> c < ' '
	? "\\u" + "0".repeat(4 - Integer.toHexString(c).length()) + Integer.toHexString(c)
	: String.valueOf(c);
	};
	buf.append(escaped);
	}
	return buf.toString();

[Copilot]

[nitpick] Complex switch expression compressed into a single line. Should be formatted with proper line breaks and spacing for better readability.

Suggested change

	return switch(value){case null->null;case String s->s;case java.util.Date d->toString(d,pattern);case Number n->toString(n,pattern);case byte[]bytes->Base64Util.encode(bytes);default->value.toString();};
	return switch (value) {
	case null -> null;
	case String s -> s;
	case java.util.Date d -> toString(d, pattern);
	case Number n -> toString(n, pattern);
	case byte[] bytes -> Base64Util.encode(bytes);
	default -> value.toString();
	};

[Copilot]

[nitpick] Complex switch expression compressed into a single line. Should be formatted with proper line breaks and spacing for better readability.

Suggested change

	return switch(o){case null->null;case Long l->l;case Number n->n.longValue();case String s->toLong(s);case java.util.Date d->pattern!=null?Long.valueOf(new SimpleDateFormat(pattern).format(d)):d.getTime();case Boolean b->b?1L:0L;default->toLong(o.toString());};
	return switch (o) {
	case null -> null;
	case Long l -> l;
	case Number n -> n.longValue();
	case String s -> toLong(s);
	case java.util.Date d -> {
	if (pattern != null) {
	return Long.valueOf(new SimpleDateFormat(pattern).format(d));
	} else {
	return d.getTime();
	}
	}
	case Boolean b -> b ? 1L : 0L;
	default -> toLong(o.toString());
	};

[Copilot]

[nitpick] Complex nested switch expression compressed into a single line. Should be formatted with proper line breaks and spacing for better readability.

Suggested change

	return switch(o){case null->null;case Boolean b->b;case Number n->n.intValue()!=0;case String s->switch(s.toLowerCase()){case"true"->Boolean.TRUE;case"false","0"->Boolean.FALSE;default->Boolean.TRUE;};default->Boolean.TRUE;};
	return switch (o) {
	case null -> null;
	case Boolean b -> b;
	case Number n -> n.intValue() != 0;
	case String s -> switch (s.toLowerCase()) {
	case "true" -> Boolean.TRUE;
	case "false", "0" -> Boolean.FALSE;
	default -> Boolean.TRUE;
	};
	default -> Boolean.TRUE;
	};

[Copilot]

This method will throw NoSuchElementException if the collection is empty, because getFirst() throws this exception when called on an empty SequencedCollection. The isEmpty() check should prevent calling getFirst() when empty.

Suggested change

	return collection.isEmpty() ? null : collection.getFirst();
	if (collection.isEmpty()) {
	return null;
	}
	try {
	return collection.getFirst();
	} catch (NoSuchElementException e) {
	return null;
	}

[Copilot]

This method will throw NoSuchElementException if the collection is empty, because getLast() throws this exception when called on an empty SequencedCollection. The isEmpty() check should prevent calling getLast() when empty.

Suggested change

	return collection.isEmpty() ? null : collection.getLast();
	if (collection == null || collection.isEmpty()) {
	return null;
	}
	return collection.getLast();

[Copilot]

This method will throw NoSuchElementException if the map is empty, because firstEntry() throws this exception when called on an empty SequencedMap. The isEmpty() check should prevent calling firstEntry() when empty.

Suggested change

	return map.isEmpty() ? null : map.firstEntry();
	try {
	return map.firstEntry();
	} catch (NoSuchElementException e) {
	return null;
	}

[Copilot]

This method will throw NoSuchElementException if the map is empty, because lastEntry() throws this exception when called on an empty SequencedMap. The isEmpty() check should prevent calling lastEntry() when empty.

Suggested change

	return map.isEmpty() ? null : map.lastEntry();
	synchronized (map) {
	return map.isEmpty() ? null : map.lastEntry();
	}