在根节点之前的xml文件中添加换行符 [英] Adding linebreak in xml file before root node

问题描述

我正在尝试在XML文档的根节点上方的注释之后添加换行符.

I am trying to add line break after my comments above the root node in XML document.

我需要这样的东西:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!--DO NOT EDIT THIS FILE-->
<projects>
</projects>

但是我能得到的是这个(根内有换行符，但是我需要在注释后换行):

But What I was able to get is this(Line break inside the root but I need line break after the comment):

    <?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!--DO NOT EDIT THIS FILE--><projects>

</projects>

我需要在评论后添加换行符.有办法吗?

I need to add the line break just after my comment. Is there a way to do this?

我的代码:

import java.io.File;
import java.io.FileInputStream;

import javax.xml.parsers.DocumentBuilder;
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 org.w3c.dom.Comment;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Text;

public class XMLNewLine {
    /**
     * @param args
     */
    public static void main(String[] args) {
        System.out.println("Adding comment..");

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();

        dbf.setValidating(false);
        DocumentBuilder db;

        try {
            Document doc;
            StreamResult result;
            result = new StreamResult(new File("abc.xml"));
            db = dbf.newDocumentBuilder();
            doc = db.parse(new FileInputStream(new File("abc.xml")));

            Element element = doc.getDocumentElement();
            Text lineBreak = doc.createTextNode("\n");

            element.appendChild(lineBreak);
            Comment comment = doc
                    .createComment("DO NOT EDIT THIS FILE");
            element.getParentNode().insertBefore(comment, element);
            doc.getDocumentElement().normalize();
            TransformerFactory transformerFactory = TransformerFactory
                    .newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            transformer.setOutputProperty(OutputKeys.INDENT, "yes");
            transformer.transform(source, result);

        } catch (Exception e) {
            // TODO Auto-generated catch block

        }

    }
}

推荐答案

您基本上希望文本节点在注释节点之后包含换行符.

You basically want a text node containing a line break after the comment node.

Element docElem = doc.getDocumentElement();

doc.insertBefore(doc.createComment("DO NOT EDIT THIS FILE"), docElem);
doc.insertBefore(doc.createTextNode("\\n"), docElem);

编辑:似乎在 org.w3c.dom.Document 的根节点上甚至不允许仅添加空格的文本节点.这是100％正确的形式，但也无济于事.

EDIT: It seems that appending even whitespace-only text nodes is not allowed at the root node of an org.w3c.dom.Document. This is 100% formally correct, but also unhelpful.

在 Transformer 输出中呈现注释的方式由它使用的序列化程序确定(HTML，XML和纯文本输出有不同的序列化程序).在内置的XML序列化程序中，注释的末尾定义为-> -不带换行符.

The way comments are rendered in the output of the Transformer is determined by the serializer it uses (there are different serializers for HTML, XML and plain text outputs). In the built-in XML serializer the end of a comment is defined as --> - without a newline.

由于 javax.xml.transform.Transformer 的内部是硬连线的，因此序列化程序不是公共API，并且该类被标记为 final ，从而覆盖了该行为.或设置自定义序列化程序是不可能的.

Since the internals of javax.xml.transform.Transformer are hard-wired, the serializers are not public API and the class is marked as final, overriding that behavior or setting a custom serializer is impossible.

换句话说，您不走运以 clean 方式添加换行符.

In other words, you are out of luck adding your line break in a clean way.

但是，您可以以一种稍微不干净的方式安全地添加它:

You can, however, safely add it in a slightly unclean way:

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();

FileInputStream inputXml = new FileInputStream(new File("input.xml"));
Document doc = db.parse(inputXml);

// add the comment node    
doc.insertBefore(doc.createComment("THIS IS A COMMENT"), doc.getDocumentElement());

StringWriter outputXmlStringWriter = new StringWriter();
Transformer transformer = transformerFactory.newTransformer();
// "xml" + "UTF-8" "include XML declaration" is the default anyway, but let's be explicit
transformer.setOutputProperty(OutputKeys.METHOD, "xml");
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
transformer.transform(new DOMSource(doc), new StreamResult(outputXmlStringWriter));

// now insert our newline into the string & write an UTF-8 file
String outputXmlString = outputXmlStringWriter.toString()
    .replaceFirst("<!--", "\n<!--").replaceFirst("-->", "-->\n");

FileOutputStream outputXml = new FileOutputStream(new File("output.xml"));            
outputXml.write(outputXmlString.getBytes("UTF-8"));

通常不建议在XML字符串上执行搜索和替换操作，但是在这种情况下，几乎没有出错的地方.

Doing search-and-replace operations on XML strings is highly discouraged in general, but in this case there is little that can go wrong.

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