pretty-print xml in java (#11899)

* pretty-print xml in java

* simplified pom.xml

xml-2/src/main/java/com/baeldung/xml/prettyprint/XmlPrettyPrinter.java

@@ -0,0 +1,91 @@
+package com.baeldung.xml.prettyprint;
+
+import org.dom4j.DocumentHelper;
+import org.dom4j.io.OutputFormat;
+import org.dom4j.io.XMLWriter;
+import org.w3c.dom.Document;
+import org.xml.sax.InputSource;
+
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.transform.OutputKeys;
+import javax.xml.transform.Transformer;
+import javax.xml.transform.TransformerFactory;
+import javax.xml.transform.dom.DOMSource;
+import javax.xml.transform.stream.StreamResult;
+import javax.xml.transform.stream.StreamSource;
+import java.io.*;
+
+public class XmlPrettyPrinter {
+
+    public static String prettyPrintByTransformer(String xmlString, int indent, boolean ignoreDeclaration) {
+
+        try {
+            final InputSource src = new InputSource(new StringReader(xmlString));
+            final Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(src);
+
+            TransformerFactory transformerFactory = TransformerFactory.newInstance();
+            transformerFactory.setAttribute("indent-number", indent);
+            Transformer transformer = transformerFactory.newTransformer(new StreamSource(new StringReader(readPrettyPrintXslt())));
+            // Using the default transformer will create empty lines in Java9+
+//         Transformer transformer = transformerFactory.newTransformer();
+            transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
+            transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, ignoreDeclaration ? "yes" : "no");
+            transformer.setOutputProperty(OutputKeys.INDENT, "yes");
+            // Alternatively, we can set indent-size on the transformer object
+            // transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", String.valueOf(indent));
+            Writer out = new StringWriter();
+            transformer.transform(new DOMSource(document), new StreamResult(out));
+            return out.toString();
+        } catch (Exception e) {
+            throw new RuntimeException("Error occurs when pretty-printing xml:\n" + xmlString, e);
+        }
+    }
+
+
+    public static String prettyPrintByDom4j(String xmlString, int indent, boolean skipDeclaration) {
+        try {
+            final OutputFormat format = OutputFormat.createPrettyPrint();
+            format.setEncoding("UTF-8");
+            format.setIndentSize(indent);
+            format.setSuppressDeclaration(skipDeclaration);
+
+            final org.dom4j.Document document = DocumentHelper.parseText(xmlString);
+            final StringWriter sw = new StringWriter();
+            final XMLWriter writer = new XMLWriter(sw, format);
+            writer.write(document);
+            return sw.toString();
+        } catch (Exception e) {
+            throw new RuntimeException("Error occurs when pretty-printing xml:\n" + xmlString, e);
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        InputStream inputStream = XmlPrettyPrinter.class.getResourceAsStream("/xml/emails.xml");
+        String xmlString = readFromInputStream(inputStream);
+        System.out.println("Pretty printing by Transformer");
+        System.out.println("=============================================");
+        System.out.println(prettyPrintByTransformer(xmlString, 2, true));
+        System.out.println("=============================================");
+        System.out.println("Pretty printing by Dom4j");
+        System.out.println("=============================================");
+        System.out.println(prettyPrintByDom4j(xmlString, 8, false));
+        System.out.println("=============================================");
+    }
+
+
+    private static String readPrettyPrintXslt() throws IOException {
+        InputStream inputStream = XmlPrettyPrinter.class.getResourceAsStream("/xml/prettyprint.xsl");
+        return readFromInputStream(inputStream);
+    }
+
+    private static String readFromInputStream(InputStream inputStream) throws IOException {
+        StringBuilder resultStringBuilder = new StringBuilder();
+        try (BufferedReader br = new BufferedReader(new InputStreamReader(inputStream))) {
+            String line;
+            while ((line = br.readLine()) != null) {
+                resultStringBuilder.append(line).append("\n");
+            }
+        }
+        return resultStringBuilder.toString();
+    }
+}