Add IndentingXmlStreamWriter class

Author: pcastornii

toolkit-core/src/main/java/com/techsenger/toolkit/core/xml/IndentingXmlStreamWriter.java

@@ -0,0 +1,238 @@
+/*
+ * Copyright 2016-2025 Pavel Castornii.
+ *
+ * Licensed 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 com.techsenger.toolkit.core.xml;
+
+import javax.xml.namespace.NamespaceContext;
+import javax.xml.stream.XMLStreamException;
+import javax.xml.stream.XMLStreamWriter;
+
+/**
+ * Decorator over {@link XMLStreamWriter} that adds pretty-print indentation.
+ *
+ * <p>Standard StAX API has no built-in support for indentation — output is compact by default. This class wraps any
+ * {@link XMLStreamWriter} and inserts newlines and indentation before each element, making the resulting XML
+ * human-readable.
+ *
+ * <p>All methods delegate to the underlying writer; only element-related methods
+ * ({@code writeStartElement}, {@code writeEndElement}, {@code writeEmptyElement}) are intercepted to inject whitespace.
+ *
+ * <p>Example usage:
+ * <pre>{@code
+ * XMLStreamWriter raw = XMLOutputFactory.newInstance()
+ *     .createXMLStreamWriter(Files.newOutputStream(path), "UTF-8");
+ *
+ * XMLStreamWriter xml = new IndentingXMLStreamWriter(raw);
+ *
+ * xml.writeStartElement(...);
+ * ...
+ * xml.writeEndDocument();
+ * xml.flush();
+ * }</pre>
+ *
+ * @author Pavel Castornii
+ */
+public class IndentingXmlStreamWriter implements XMLStreamWriter, AutoCloseable {
+
+    private final XMLStreamWriter delegate;
+    private final String indent;
+    private int depth = 0;
+
+    public IndentingXmlStreamWriter(XMLStreamWriter delegate) {
+        this(delegate, "    ");
+    }
+
+    public IndentingXmlStreamWriter(XMLStreamWriter delegate, String indent) {
+        this.delegate = delegate;
+        this.indent = indent;
+    }
+
+    @Override
+    public void writeStartElement(String localName) throws XMLStreamException {
+        writeIndent();
+        delegate.writeStartElement(localName);
+        depth++;
+    }
+
+    @Override
+    public void writeStartElement(String namespaceURI, String localName) throws XMLStreamException {
+        writeIndent();
+        delegate.writeStartElement(namespaceURI, localName);
+        depth++;
+    }
+
+    @Override
+    public void writeStartElement(String prefix, String localName, String namespaceURI) throws XMLStreamException {
+        writeIndent();
+        delegate.writeStartElement(prefix, localName, namespaceURI);
+        depth++;
+    }
+
+    @Override
+    public void writeEndElement() throws XMLStreamException {
+        depth--;
+        writeIndent();
+        delegate.writeEndElement();
+    }
+
+    @Override
+    public void writeEmptyElement(String localName) throws XMLStreamException {
+        writeIndent();
+        delegate.writeEmptyElement(localName);
+    }
+
+    @Override
+    public void writeEmptyElement(String namespaceURI, String localName) throws XMLStreamException {
+        writeIndent();
+        delegate.writeEmptyElement(namespaceURI, localName);
+    }
+
+    @Override
+    public void writeEmptyElement(String prefix, String localName, String namespaceURI) throws XMLStreamException {
+        writeIndent();
+        delegate.writeEmptyElement(prefix, localName, namespaceURI);
+    }
+
+    @Override
+    public void writeStartDocument() throws XMLStreamException {
+        delegate.writeStartDocument();
+    }
+
+    @Override
+    public void writeStartDocument(String version) throws XMLStreamException {
+        delegate.writeStartDocument(version);
+    }
+
+    @Override
+    public void writeStartDocument(String encoding, String version) throws XMLStreamException {
+        delegate.writeStartDocument(encoding, version);
+    }
+
+    @Override
+    public void writeEndDocument() throws XMLStreamException {
+        delegate.writeEndDocument();
+    }
+
+    @Override
+    public void writeAttribute(String localName, String value) throws XMLStreamException {
+        delegate.writeAttribute(localName, value);
+    }
+
+    @Override
+    public void writeAttribute(String namespaceURI, String localName, String value) throws XMLStreamException {
+        delegate.writeAttribute(namespaceURI, localName, value);
+    }
+
+    @Override
+    public void writeAttribute(String prefix, String namespaceURI, String localName, String value)
+            throws XMLStreamException {
+        delegate.writeAttribute(prefix, namespaceURI, localName, value);
+    }
+
+    @Override
+    public void writeCharacters(String text) throws XMLStreamException {
+        delegate.writeCharacters(text);
+    }
+
+    @Override
+    public void writeCharacters(char[] text, int start, int len) throws XMLStreamException {
+        delegate.writeCharacters(text, start, len);
+    }
+
+    @Override
+    public void writeCData(String data) throws XMLStreamException {
+        delegate.writeCData(data);
+    }
+
+    @Override
+    public void writeComment(String data) throws XMLStreamException {
+        delegate.writeComment(data);
+    }
+
+    @Override
+    public void writeNamespace(String prefix, String namespaceURI) throws XMLStreamException {
+        delegate.writeNamespace(prefix, namespaceURI);
+    }
+
+    @Override
+    public void writeDefaultNamespace(String namespaceURI) throws XMLStreamException {
+        delegate.writeDefaultNamespace(namespaceURI);
+    }
+
+    @Override
+    public void writeProcessingInstruction(String target) throws XMLStreamException {
+        delegate.writeProcessingInstruction(target);
+    }
+
+    @Override
+    public void writeProcessingInstruction(String target, String data) throws XMLStreamException {
+        delegate.writeProcessingInstruction(target, data);
+    }
+
+    @Override
+    public void writeEntityRef(String name) throws XMLStreamException {
+        delegate.writeEntityRef(name);
+    }
+
+    @Override
+    public void writeDTD(String dtd) throws XMLStreamException {
+        delegate.writeDTD(dtd);
+    }
+
+    @Override
+    public void flush() throws XMLStreamException {
+        delegate.flush();
+    }
+
+    @Override
+    public void close() throws XMLStreamException {
+        delegate.close();
+    }
+
+    @Override
+    public String getPrefix(String uri) throws XMLStreamException {
+        return delegate.getPrefix(uri);
+    }
+
+    @Override
+    public void setPrefix(String prefix, String uri) throws XMLStreamException {
+        delegate.setPrefix(prefix, uri);
+    }
+
+    @Override
+    public void setDefaultNamespace(String uri) throws XMLStreamException {
+        delegate.setDefaultNamespace(uri);
+    }
+
+    @Override
+    public void setNamespaceContext(NamespaceContext context) throws XMLStreamException {
+        delegate.setNamespaceContext(context);
+    }
+
+    @Override
+    public NamespaceContext getNamespaceContext() {
+        return delegate.getNamespaceContext();
+    }
+
+    @Override
+    public Object getProperty(String name) {
+        return delegate.getProperty(name);
+    }
+
+    private void writeIndent() throws XMLStreamException {
+        delegate.writeCharacters("\n" + indent.repeat(depth));
+    }
+}