[BAEL-7043] mutable strings (#15112)
Co-authored-by: Bhaskar <bhaskar.dastidar@freshworks.com>
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Bhaskar Ghosh Dastidar
GitHub
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package com.baeldung.mutablestrings;
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import java.nio.ByteBuffer;
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import java.nio.CharBuffer;
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import java.nio.charset.CharacterCodingException;
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import java.nio.charset.Charset;
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import java.nio.charset.CharsetDecoder;
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import java.nio.charset.CharsetEncoder;
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import java.nio.charset.CoderResult;
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public class CharsetUsageExample {
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public ByteBuffer encodeString(String inputString) {
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Charset charset = Charset.forName("UTF-8");
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CharsetEncoder encoder = charset.newEncoder();
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CharBuffer charBuffer = CharBuffer.wrap(inputString);
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ByteBuffer byteBuffer = ByteBuffer.allocate(50);
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encoder.encode(charBuffer, byteBuffer, true); // true indicates the end of input
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byteBuffer.flip();
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return byteBuffer;
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}
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public String decodeString(ByteBuffer byteBuffer) {
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Charset charset = Charset.forName("UTF-8");
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CharsetDecoder decoder = charset.newDecoder();
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CharBuffer decodedCharBuffer = CharBuffer.allocate(50);
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decoder.decode(byteBuffer, decodedCharBuffer, true);
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decodedCharBuffer.flip();
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return decodedCharBuffer.toString();
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}
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}
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package com.baeldung.mutablestrings;
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import java.nio.ByteBuffer;
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import java.nio.CharBuffer;
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import java.nio.charset.Charset;
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import java.nio.charset.CharsetDecoder;
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import java.nio.charset.CharsetEncoder;
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import java.nio.charset.CoderResult;
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import java.util.concurrent.atomic.AtomicReference;
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public class MutableStringUsingCharset {
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private final AtomicReference<CharBuffer> cbRef = new AtomicReference<>();
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private final Charset myCharset = new Charset("mycharset", null) {
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@Override
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public boolean contains(Charset cs) {
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return false;
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}
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@Override
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public CharsetDecoder newDecoder() {
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return new CharsetDecoder(this, 1.0f, 1.0f) {
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@Override
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protected CoderResult decodeLoop(ByteBuffer in, CharBuffer out) {
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cbRef.set(out);
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while (in.remaining() > 0) {
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out.append((char) in.get());
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}
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return CoderResult.UNDERFLOW;
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}
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};
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}
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@Override
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public CharsetEncoder newEncoder() {
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CharsetEncoder cd = new CharsetEncoder(this, 1.0f, 1.0f) {
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@Override
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protected CoderResult encodeLoop(CharBuffer in, ByteBuffer out) {
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while (in.hasRemaining()) {
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if (!out.hasRemaining()) {
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return CoderResult.OVERFLOW;
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}
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char currentChar = in.get();
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if (currentChar > 127) {
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return CoderResult.unmappableForLength(1);
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}
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out.put((byte) currentChar);
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}
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return CoderResult.UNDERFLOW;
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}
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};
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return cd;
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}
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};
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public String createModifiableString(String s) {
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return new String(s.getBytes(), myCharset);
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}
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public void modifyString() {
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CharBuffer cb = cbRef.get();
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cb.position(0);
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cb.put("xyz");
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}
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}
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@ -0,0 +1,24 @@
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package com.baeldung.mutablestrings;
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import java.lang.reflect.Field;
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import java.nio.charset.Charset;
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import com.google.errorprone.annotations.DoNotCall;
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public class MutableStrings {
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/**
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* This involves using Reflection to change String fields and it is not encouraged to use this in programs.
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* @throws NoSuchFieldException
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* @throws IllegalAccessException
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*/
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@DoNotCall
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public void mutableUsingReflection() throws NoSuchFieldException, IllegalAccessException {
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String myString = "Hello World";
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String otherString = new String("Hello World");
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Field f = String.class.getDeclaredField("value");
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f.setAccessible(true);
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f.set(myString, "Hi World".toCharArray());
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System.out.println(otherString);
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}
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}
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@ -0,0 +1,17 @@
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package com.baeldung.mutablestring;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Test;
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import com.baeldung.mutablestrings.CharsetUsageExample;
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public class CharsetUsageUnitTest {
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@Test
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public void givenCharset_whenStringIsEncodedAndDecoded_thenGivesCorrectResult() {
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CharsetUsageExample ch = new CharsetUsageExample();
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String inputString = "hello दुनिया";
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String result = ch.decodeString(ch.encodeString(inputString));
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Assertions.assertEquals(inputString, result);
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}
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}
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@ -0,0 +1,24 @@
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package com.baeldung.mutablestring;
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import org.junit.Assert;
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import org.junit.jupiter.api.Disabled;
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import org.junit.jupiter.api.Test;
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import com.baeldung.mutablestrings.MutableStringUsingCharset;
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public class MutableStringUsingCharsetUnitTest {
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@Test
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@Disabled
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/**
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* This test is disabled as it works well for Java 8 and below
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*/
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public void givenCustomCharSet_whenStringUpdated_StringGetsMutated() throws Exception {
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MutableStringUsingCharset ms = new MutableStringUsingCharset();
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String s = ms.createModifiableString("Hello");
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Assert.assertEquals("Hello", s);
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ms.modifyString();
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Assert.assertEquals("something", s);
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}
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}
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