1 files changed, 165 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/io/output/AppendableWriter.java b/src/main/java/org/apache/commons/io/output/AppendableWriter.java
new file mode 100644
index 00000000..8e234e64
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+++ b/src/main/java/org/apache/commons/io/output/AppendableWriter.java
@@ -0,0 +1,165 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.io.output;
+
+import java.io.IOException;
+import java.io.Writer;
+import java.util.Objects;
+
+/**
+ * Writer implementation that writes the data to an {@link Appendable}
+ * Object.
+ * <p>
+ * For example, can be used with a {@link java.lang.StringBuilder}
+ * or {@link java.lang.StringBuffer}.
+ * </p>
+ *
+ * @since 2.7
+ * @see Appendable
+ *
+ * @param <T> The type of the {@link Appendable} wrapped by this AppendableWriter.
+ */
+public class AppendableWriter <T extends Appendable> extends Writer {
+
+    private final T appendable;
+
+    /**
+     * Constructs a new instance with the specified appendable.
+     *
+     * @param appendable the appendable to write to
+     */
+    public AppendableWriter(final T appendable) {
+        this.appendable = appendable;
+    }
+
+    /**
+     * Appends the specified character to the underlying appendable.
+     *
+     * @param c the character to append
+     * @return this writer
+     * @throws IOException upon error
+     */
+    @Override
+    public Writer append(final char c) throws IOException {
+        appendable.append(c);
+        return this;
+    }
+
+    /**
+     * Appends the specified character sequence to the underlying appendable.
+     *
+     * @param csq the character sequence to append
+     * @return this writer
+     * @throws IOException upon error
+     */
+    @Override
+    public Writer append(final CharSequence csq) throws IOException {
+        appendable.append(csq);
+        return this;
+    }
+
+    /**
+     * Appends a subsequence of the specified character sequence to the underlying appendable.
+     *
+     * @param csq the character sequence from which a subsequence will be appended
+     * @param start the index of the first character in the subsequence
+     * @param end the index of the character following the last character in the subsequence
+     * @return this writer
+     * @throws IOException upon error
+     */
+    @Override
+    public Writer append(final CharSequence csq, final int start, final int end) throws IOException {
+        appendable.append(csq, start, end);
+        return this;
+    }
+
+    /**
+     * Closes the stream. This implementation does nothing.
+     *
+     * @throws IOException upon error
+     */
+    @Override
+    public void close() throws IOException {
+        // noop
+    }
+
+    /**
+     * Flushes the stream. This implementation does nothing.
+     *
+     * @throws IOException upon error
+     */
+    @Override
+    public void flush() throws IOException {
+        // noop
+    }
+
+    /**
+     * Return the target appendable.
+     *
+     * @return the target appendable
+     */
+    public T getAppendable() {
+        return appendable;
+    }
+
+    /**
+     * Writes a portion of an array of characters to the underlying appendable.
+     *
+     * @param cbuf an array with the characters to write
+     * @param off offset from which to start writing characters
+     * @param len number of characters to write
+     * @throws IOException upon error
+     */
+    @Override
+    public void write(final char[] cbuf, final int off, final int len) throws IOException {
+        Objects.requireNonNull(cbuf, "Character array is missing");
+        if (len < 0 || off + len > cbuf.length) {
+            throw new IndexOutOfBoundsException("Array Size=" + cbuf.length +
+                    ", offset=" + off + ", length=" + len);
+        }
+        for (int i = 0; i < len; i++) {
+            appendable.append(cbuf[off + i]);
+        }
+    }
+
+    /**
+     * Writes a character to the underlying appendable.
+     *
+     * @param c the character to write
+     * @throws IOException upon error
+     */
+    @Override
+    public void write(final int c) throws IOException {
+        appendable.append((char)c);
+    }
+
+    /**
+     * Writes a portion of a String to the underlying appendable.
+     *
+     * @param str a string
+     * @param off offset from which to start writing characters
+     * @param len number of characters to write
+     * @throws IOException upon error
+     */
+    @Override
+    public void write(final String str, final int off, final int len) throws IOException {
+        // appendable.append will add "null" for a null String; add an explicit null check
+        Objects.requireNonNull(str, "String is missing");
+        appendable.append(str, off, off + len);
+    }
+
+}