如何从Java打印XML？

pretty-print java xml

2022-08-31 04:25:57

我有一个包含XML的Java字符串，没有换行符或缩进。我想把它变成一个带有格式良好的XML的字符串。我该怎么做？

String unformattedXml = "<tag><nested>hello</nested></tag>";
String formattedXml = new [UnknownClass]().format(unformattedXml);

注意：我的输入是一个字符串。我的输出是一个字符串。

（基本）模拟结果：

<?xml version="1.0" encoding="UTF-8"?>
<root>
  <tag>
    <nested>hello</nested>
  </tag>
</root>

答案 1

import org.xml.sax.InputSource;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.StringReader;
import java.io.StringWriter;

public class XmlPrettyPrint {
  private static String format( final String xml ) throws Exception {
    final var transformer = TransformerFactory.newInstance().newTransformer();
    final var result = new StreamResult( new StringWriter() );
    final var dbf = DocumentBuilderFactory.newInstance();
    final var db = dbf.newDocumentBuilder();
    final var is = new InputSource( new StringReader( xml ) );
    final var source = new DOMSource( db.parse( is ) );

    transformer.setOutputProperty( OutputKeys.INDENT, "yes" );
    transformer.setOutputProperty( "{http://xml.apache.org/xslt}indent-amount",
                                   String.valueOf( 2 ) );
    transformer.transform( source, result );

    return result.getWriter().toString();
  }
}

用法示例：

final var unformattedXml = "<hello><world/></hello>";
final var formattedXml = XmlPrettyPrint.format( unformattedXml );

结果：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<hello>
  <world/>
</hello>

注意：结果可能因 Java 版本而异。搜索特定于您的平台的解决方法。

答案 2

以下是我自己问题的答案。我将各种结果中的答案组合在一起，编写了一个可以打印 XML 的类。

不保证它如何使用无效的 XML 或大型文档进行响应。

package ecb.sdw.pretty;

import org.apache.xml.serialize.OutputFormat;
import org.apache.xml.serialize.XMLSerializer;
import org.w3c.dom.Document;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.io.Writer;

/**
 * Pretty-prints xml, supplied as a string.
 * <p/>
 * eg.
 * <code>
 * String formattedXml = new XmlFormatter().format("<tag><nested>hello</nested></tag>");
 * </code>
 */
public class XmlFormatter {

    public XmlFormatter() {
    }

    public String format(String unformattedXml) {
        try {
            final Document document = parseXmlFile(unformattedXml);

            OutputFormat format = new OutputFormat(document);
            format.setLineWidth(65);
            format.setIndenting(true);
            format.setIndent(2);
            Writer out = new StringWriter();
            XMLSerializer serializer = new XMLSerializer(out, format);
            serializer.serialize(document);

            return out.toString();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private Document parseXmlFile(String in) {
        try {
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = dbf.newDocumentBuilder();
            InputSource is = new InputSource(new StringReader(in));
            return db.parse(is);
        } catch (ParserConfigurationException e) {
            throw new RuntimeException(e);
        } catch (SAXException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) {
        String unformattedXml =
                "<?xml version=\"1.0\" encoding=\"UTF-8\"?><QueryMessage\n" +
                        "        xmlns=\"http://www.SDMX.org/resources/SDMXML/schemas/v2_0/message\"\n" +
                        "        xmlns:query=\"http://www.SDMX.org/resources/SDMXML/schemas/v2_0/query\">\n" +
                        "    <Query>\n" +
                        "        <query:CategorySchemeWhere>\n" +
                        "   \t\t\t\t\t         <query:AgencyID>ECB\n\n\n\n</query:AgencyID>\n" +
                        "        </query:CategorySchemeWhere>\n" +
                        "    </Query>\n\n\n\n\n" +
                        "</QueryMessage>";

        System.out.println(new XmlFormatter().format(unformattedXml));
    }

}