我有一个包含XML的Java字符串,没有换行或缩进。我想把它变成一个字符串与格式良好的XML。我怎么做呢?

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。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>

当前回答

稍微改进了milosmns的版本…

public static String getPrettyXml(String xml) {
    if (xml == null || xml.trim().length() == 0) return "";

    int stack = 0;
    StringBuilder pretty = new StringBuilder();
    String[] rows = xml.trim().replaceAll(">", ">\n").replaceAll("<", "\n<").split("\n");

    for (int i = 0; i < rows.length; i++) {
        if (rows[i] == null || rows[i].trim().length() == 0) continue;

        String row = rows[i].trim();
        if (row.startsWith("<?")) {
            pretty.append(row + "\n");
        } else if (row.startsWith("</")) {
            String indent = repeatString(--stack);
            pretty.append(indent + row + "\n");
        } else if (row.startsWith("<") && row.endsWith("/>") == false) {
            String indent = repeatString(stack++);
            pretty.append(indent + row + "\n");
            if (row.endsWith("]]>")) stack--;
        } else {
            String indent = repeatString(stack);
            pretty.append(indent + row + "\n");
        }
    }

    return pretty.toString().trim();
}

private static String repeatString(int stack) {
     StringBuilder indent = new StringBuilder();
     for (int i = 0; i < stack; i++) {
        indent.append(" ");
     }
     return indent.toString();
} 

其他回答

请注意,排名靠前的答案需要使用xerces。

如果您不想添加这个外部依赖,那么您可以简单地使用标准jdk库(实际上是在内部使用xerces构建的)。

注意:jdk 1.5版本有一个bug,请参阅http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6296446,但现在已经解决了。

(注意,如果发生错误,将返回原始文本)

package com.test;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;

import javax.xml.transform.OutputKeys;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.sax.SAXSource;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.stream.StreamResult;

import org.xml.sax.InputSource;

public class XmlTest {
    public static void main(String[] args) {
        XmlTest t = new XmlTest();
        System.out.println(t.formatXml("<a><b><c/><d>text D</d><e value='0'/></b></a>"));
    }

    public String formatXml(String xml){
        try{
            Transformer serializer= SAXTransformerFactory.newInstance().newTransformer();
            serializer.setOutputProperty(OutputKeys.INDENT, "yes");
            //serializer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
            serializer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
            //serializer.setOutputProperty("{http://xml.customer.org/xslt}indent-amount", "2");
            Source xmlSource=new SAXSource(new InputSource(new ByteArrayInputStream(xml.getBytes())));
            StreamResult res =  new StreamResult(new ByteArrayOutputStream());            
            serializer.transform(xmlSource, res);
            return new String(((ByteArrayOutputStream)res.getOutputStream()).toByteArray());
        }catch(Exception e){
            //TODO log error
            return xml;
        }
    }

}
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
// initialize StreamResult with File object to save to file
StreamResult result = new StreamResult(new StringWriter());
DOMSource source = new DOMSource(doc);
transformer.transform(source, result);
String xmlString = result.getWriter().toString();
System.out.println(xmlString);

注意:根据Java版本的不同,结果可能有所不同。搜索特定于您的平台的解决方案。

除了max、codeskrap、David Easley和milosmns给出的答案外,还可以看看我的轻量级、高性能漂亮打印机库:xml-formatter

// construct lightweight, threadsafe, instance
PrettyPrinter prettyPrinter = PrettyPrinterBuilder.newPrettyPrinter().build();

StringBuilder buffer = new StringBuilder();
String xml = ..; // also works with char[] or Reader

if(prettyPrinter.process(xml, buffer)) {
     // valid XML, print buffer
} else {
     // invalid XML, print xml
}

有时,就像直接从文件运行模拟SOAP服务时,有一个漂亮的打印机也能处理已经打印好的XML是很好的:

PrettyPrinter prettyPrinter = PrettyPrinterBuilder.newPrettyPrinter().ignoreWhitespace().build();

正如一些人评论的那样,漂亮打印只是一种以更适合人类阅读的形式表示XML的方法——严格来说,XML数据中不应该有空格。

该库用于日志记录的漂亮打印,还包括用于过滤(子树移除/匿名化)和漂亮打印CDATA和Text节点中的XML的函数。

为了将来的参考,这里有一个对我有用的解决方案(感谢@George Hawkins在其中一个答案中发表的评论):

DOMImplementationRegistry registry = DOMImplementationRegistry.newInstance();
DOMImplementationLS impl = (DOMImplementationLS) registry.getDOMImplementation("LS");
LSSerializer writer = impl.createLSSerializer();
writer.getDomConfig().setParameter("format-pretty-print", Boolean.TRUE);
LSOutput output = impl.createLSOutput();
ByteArrayOutputStream out = new ByteArrayOutputStream();
output.setByteStream(out);
writer.write(document, output);
String xmlStr = new String(out.toByteArray());

稍微改进了milosmns的版本…

public static String getPrettyXml(String xml) {
    if (xml == null || xml.trim().length() == 0) return "";

    int stack = 0;
    StringBuilder pretty = new StringBuilder();
    String[] rows = xml.trim().replaceAll(">", ">\n").replaceAll("<", "\n<").split("\n");

    for (int i = 0; i < rows.length; i++) {
        if (rows[i] == null || rows[i].trim().length() == 0) continue;

        String row = rows[i].trim();
        if (row.startsWith("<?")) {
            pretty.append(row + "\n");
        } else if (row.startsWith("</")) {
            String indent = repeatString(--stack);
            pretty.append(indent + row + "\n");
        } else if (row.startsWith("<") && row.endsWith("/>") == false) {
            String indent = repeatString(stack++);
            pretty.append(indent + row + "\n");
            if (row.endsWith("]]>")) stack--;
        } else {
            String indent = repeatString(stack);
            pretty.append(indent + row + "\n");
        }
    }

    return pretty.toString().trim();
}

private static String repeatString(int stack) {
     StringBuilder indent = new StringBuilder();
     for (int i = 0; i < stack; i++) {
        indent.append(" ");
     }
     return indent.toString();
}