improve string parsing performance with CharSequenceReader

Author: Simulant87

src/main/java/org/json/CharSequenceReader.java

@@ -0,0 +1,101 @@
+package org.json;
+
+import java.io.Reader;
+
+/**
+ * a Reader to read from a {@link CharSequence} e.g. a {@link String}.
+ */
+public class CharSequenceReader extends Reader {
+
+    private final CharSequence charSequence;
+    private int index;
+    private int markedIndex;
+
+    /**
+     * creates a new CharSequenceReader to read from the given CharSequence
+     * @param charSequence the input to read.
+     */
+    public CharSequenceReader(CharSequence charSequence) {
+        this.charSequence = charSequence;
+    }
+
+    /**
+     * reads the next character from the input.
+     * @return returns the read character or -1 if the end of the input is reached.
+     */
+    @Override
+    public int read() {
+        if (index < charSequence.length()) {
+            return charSequence.charAt(index++);
+        }
+        return -1;
+    }
+
+
+    /**
+     * reads a maximum number of characters from the input into the charBuffer starting at the offset
+     * and returns the number of actual read characters.
+     *
+     * @param charBuffer the target charBuffer to write the read characters into
+     * @param offset the offset index where to start writing into the charBuffer
+     * @param length the maximum number of characters to read
+     * @return the number of characters read into the charBuffer or -1 if the end of the input is reached.
+     */
+    @Override
+    public int read(char[] charBuffer, int offset, int length) {
+        if (charBuffer == null) {
+            throw new NullPointerException("The target charBuffer cannot be null");
+        } else if (offset < 0) {
+            throw new IndexOutOfBoundsException("Offset must not be negative");
+        } else if (length < 0) {
+            throw new IndexOutOfBoundsException("Length must not be negative");
+        } else if (offset + length > charBuffer.length) {
+            throw new IndexOutOfBoundsException("Offset + length must not be larger than the charBuffer length");
+        } else if (index >= charSequence.length()) {
+            return -1;
+        }
+
+        int charsToRead = Math.min(length, charSequence.length() - index);
+        for (int i = 0; i < charsToRead; i++) {
+            charBuffer[offset + i] = charSequence.charAt(index++);
+        }
+
+        return charsToRead;
+    }
+
+    /**
+     * returns true to indicate that mark is supported.
+     * @return true
+     */
+    @Override
+    public boolean markSupported() {
+        return true;
+    }
+
+    /**
+     * marks the reader on the current position to later jump back to it by using {@link #reset()}.
+     * @param readAheadLimit will be ignored. This reader has no readAheadLimit.
+     */
+    @Override
+    public void mark(int readAheadLimit) {
+        markedIndex = this.index;
+    }
+
+    /**
+     * resets the reader to the previous marked position used by {@link #mark(int)}.
+     */
+    @Override
+    public void reset() {
+        index = markedIndex;
+    }
+
+
+    /**
+     * does nothing.
+     */
+    @Override
+    public void close() {
+
+    }
+
+}

src/main/java/org/json/JSONTokener.java

@@ -67,7 +67,7 @@ public JSONTokener(InputStream inputStream) {
      * @param s     A source string.
      */
     public JSONTokener(String s) {
-        this(new StringReader(s));
+        this(new CharSequenceReader(s));
     }
 
 

src/test/java/org/json/junit/CharSequenceReaderTest.java

@@ -0,0 +1,88 @@
+package org.json.junit;
+
+import org.json.CharSequenceReader;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class CharSequenceReaderTest {
+
+    @Test
+    public void testReadSingleCharacter() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        assertEquals('t', reader.read());
+        assertEquals('e', reader.read());
+        assertEquals('s', reader.read());
+        assertEquals('t', reader.read());
+        assertEquals(-1, reader.read());
+        assertEquals(-1, reader.read());
+    }
+
+    @Test
+    public void testReadToCharBuffer() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        char[] buffer = new char[10];
+        int read = reader.read(buffer, 2, 3);
+        assertEquals(3, read);
+        assertArrayEquals(new char[]{0, 0, 't', 'e', 's', 0, 0, 0, 0, 0}, buffer);
+    }
+
+    @Test
+    public void testReadPastEnd() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        char[] buffer = new char[5];
+        assertEquals(4, reader.read(buffer, 0, 5));
+        assertEquals(-1, reader.read(buffer, 0, 5));
+    }
+
+    @Test
+    public void testMarkAndReset() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        assertEquals('t', reader.read());
+        reader.mark(0);
+        assertEquals('e', reader.read());
+        assertEquals('s', reader.read());
+        reader.reset();
+        assertEquals('e', reader.read());
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void testReadToNullBuffer() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        reader.read(null, 0, 1);
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testNegativeOffset() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        char[] buffer = new char[10];
+        reader.read(buffer, -1, 5);
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testNegativeLength() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        char[] buffer = new char[10];
+        reader.read(buffer, 0, -5);
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testOffsetPlusLengthExceedsBuffer() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        char[] buffer = new char[5];
+        reader.read(buffer, 3, 3);
+    }
+
+    @Test
+    public void testCloseDoesNothing() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        reader.close();
+        assertEquals('t', reader.read());
+    }
+
+    @Test
+    public void testMarkSupported() {
+        CharSequenceReader reader = new CharSequenceReader("test");
+        assertTrue(reader.markSupported());
+    }
+}