java base64写入xml

要将Base64编码的数据写入XML文件，可以按照以下步骤进行操作：

1. 将Base64编码的数据解码为字节数组。

byte[] decodedData = Base64.getDecoder().decode(base64Data);

2. 创建一个`Document`对象并添加根元素。

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.newDocument();

Element rootElement = doc.createElement("root");
doc.appendChild(rootElement);

3. 创建一个子元素，将解码后的数据作为其文本内容。

Element dataElement = doc.createElement("data");
dataElement.setTextContent(new String(decodedData));
rootElement.appendChild(dataElement);

4. 将`Document`对象写入XML文件。

TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
transformer.setOutputProperty(OutputKeys.INDENT, "yes");

FileOutputStream fos = new FileOutputStream("output.xml");
transformer.transform(new DOMSource(doc), new StreamResult(fos));
fos.close();

完整代码示例：

import java.io.FileOutputStream;
import java.util.Base64;

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.Document;
import org.w3c.dom.Element;

public class Base64ToXML {
    public static void main(String[] args) throws Exception {
        String base64Data = "SGVsbG8gV29ybGQh"; // Base64编码的数据

        byte[] decodedData = Base64.getDecoder().decode(base64Data);

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.newDocument();

        Element rootElement = doc.createElement("root");
        doc.appendChild(rootElement);

        Element dataElement = doc.createElement("data");
        dataElement.setTextContent(new String(decodedData));
        rootElement.appendChild(dataElement);

        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer transformer = tf.newTransformer();
        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");

        FileOutputStream fos = new FileOutputStream("output.xml");
        transformer.transform(new DOMSource(doc), new StreamResult(fos));
        fos.close();
    }
}

执行后会生成一个名为`output.xml`的文件，内容如下：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<root>
    <data>Hello World!</data>
</root>