所提供的代码应被视为草图而不是权威文章。我不是 SAX 方面的专家，可以改进实现以获得更好的性能、更简单的代码等。也就是说 SAX 应该能够处理大型 XML 文件的流处理。
我会使用 SAX 解析器通过 2 次传递来解决这个问题。 （顺便说一句，我还将使用 CSV 生成库来创建输出，因为这将处理 CSV 涉及的所有繁琐字符转义，但我还没有在我的草图中实现这一点）。
第一关：
确定标题列数
第二遍：
输出 CSV
我假设 XML 文件格式正确。我假设我们没有预定义顺序的方案/DTD。
在第一遍中，我假设将为每个包含文本内容的 XML 元素或任何属性添加一个 CSV 列（我假设属性将包含一些东西！）。
第二遍，已经确定了目标列的数量，将进行实际的 CSV 输出。
根据您的示例 XML，我的代码草图将生成：
ItemID,StartTime,EndTime,ViewItemURL,AverageTime,category,category,type,type,AveragePrice
4504216603,10:00:10.000Z,10:00:30.000Z,http://url,,,,,,
4504216604,10:30:10.000Z,11:00:10.000Z,http://url,value1,9823,9112,TX,TY,value2
请注意，我使用了 google 集合 LinkedHashMultimap，因为这在将多个值与单个键关联时很有帮助。我希望你觉得这很有用！
import com.google.common.collect.LinkedHashMultimap;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map.Entry;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.helpers.XMLReaderFactory;
public class App {
public static void main(String[] args) throws SAXException, FileNotFoundException, IOException {
// First pass - to determine headers
XMLReader xr = XMLReaderFactory.createXMLReader();
HeaderHandler handler = new HeaderHandler();
xr.setContentHandler(handler);
xr.setErrorHandler(handler);
FileReader r = new FileReader("test1.xml");
xr.parse(new InputSource(r));
LinkedHashMap<String, Integer> headers = handler.getHeaders();
int totalnumberofcolumns = 0;
for (int headercount : headers.values()) {
totalnumberofcolumns += headercount;
}
String[] columnheaders = new String[totalnumberofcolumns];
int i = 0;
for (Entry<String, Integer> entry : headers.entrySet()) {
for (int j = 0; j < entry.getValue(); j++) {
columnheaders[i] = entry.getKey();
i++;
}
}
StringBuilder sb = new StringBuilder();
for (String h : columnheaders) {
sb.append(h);
sb.append(',');
}
System.out.println(sb.substring(0, sb.length() - 1));
// Second pass - collect and output data
xr = XMLReaderFactory.createXMLReader();
DataHandler datahandler = new DataHandler();
datahandler.setHeaderArray(columnheaders);
xr.setContentHandler(datahandler);
xr.setErrorHandler(datahandler);
r = new FileReader("test1.xml");
xr.parse(new InputSource(r));
}
public static class HeaderHandler extends DefaultHandler {
private String content;
private String currentElement;
private boolean insideElement = false;
private Attributes attribs;
private LinkedHashMap<String, Integer> itemHeader;
private LinkedHashMap<String, Integer> accumulativeHeader = new LinkedHashMap<String, Integer>();
public HeaderHandler() {
super();
}
private LinkedHashMap<String, Integer> getHeaders() {
return accumulativeHeader;
}
private void addItemHeader(String headerName) {
if (itemHeader.containsKey(headerName)) {
itemHeader.put(headerName, itemHeader.get(headerName) + 1);
} else {
itemHeader.put(headerName, 1);
}
}
@Override
public void startElement(String uri, String name,
String qName, Attributes atts) {
if ("item".equalsIgnoreCase(qName)) {
itemHeader = new LinkedHashMap<String, Integer>();
}
currentElement = qName;
content = null;
insideElement = true;
attribs = atts;
}
@Override
public void endElement(String uri, String name, String qName) {
if (!"item".equalsIgnoreCase(qName) && !"root".equalsIgnoreCase(qName)) {
if (content != null && qName.equals(currentElement) && content.trim().length() > 0) {
addItemHeader(qName);
}
if (attribs != null) {
int attsLength = attribs.getLength();
if (attsLength > 0) {
for (int i = 0; i < attsLength; i++) {
String attName = attribs.getLocalName(i);
addItemHeader(attName);
}
}
}
}
if ("item".equalsIgnoreCase(qName)) {
for (Entry<String, Integer> entry : itemHeader.entrySet()) {
String headerName = entry.getKey();
Integer count = entry.getValue();
//System.out.println(entry.getKey() + ":" + entry.getValue());
if (accumulativeHeader.containsKey(headerName)) {
if (count > accumulativeHeader.get(headerName)) {
accumulativeHeader.put(headerName, count);
}
} else {
accumulativeHeader.put(headerName, count);
}
}
}
insideElement = false;
currentElement = null;
attribs = null;
}
@Override
public void characters(char ch[], int start, int length) {
if (insideElement) {
content = new String(ch, start, length);
}
}
}
public static class DataHandler extends DefaultHandler {
private String content;
private String currentElement;
private boolean insideElement = false;
private Attributes attribs;
private LinkedHashMultimap dataMap;
private String[] headerArray;
public DataHandler() {
super();
}
@Override
public void startElement(String uri, String name,
String qName, Attributes atts) {
if ("item".equalsIgnoreCase(qName)) {
dataMap = LinkedHashMultimap.create();
}
currentElement = qName;
content = null;
insideElement = true;
attribs = atts;
}
@Override
public void endElement(String uri, String name, String qName) {
if (!"item".equalsIgnoreCase(qName) && !"root".equalsIgnoreCase(qName)) {
if (content != null && qName.equals(currentElement) && content.trim().length() > 0) {
dataMap.put(qName, content);
}
if (attribs != null) {
int attsLength = attribs.getLength();
if (attsLength > 0) {
for (int i = 0; i < attsLength; i++) {
String attName = attribs.getLocalName(i);
dataMap.put(attName, attribs.getValue(i));
}
}
}
}
if ("item".equalsIgnoreCase(qName)) {
String data[] = new String[headerArray.length];
int i = 0;
for (String h : headerArray) {
if (dataMap.containsKey(h)) {
Object[] values = dataMap.get(h).toArray();
data[i] = (String) values[0];
if (values.length > 1) {
dataMap.removeAll(h);
for (int j = 1; j < values.length; j++) {
dataMap.put(h, values[j]);
}
} else {
dataMap.removeAll(h);
}
} else {
data[i] = "";
}
i++;
}
StringBuilder sb = new StringBuilder();
for (String d : data) {
sb.append(d);
sb.append(',');
}
System.out.println(sb.substring(0, sb.length() - 1));
}
insideElement = false;
currentElement = null;
attribs = null;
}
@Override
public void characters(char ch[], int start, int length) {
if (insideElement) {
content = new String(ch, start, length);
}
}
public void setHeaderArray(String[] headerArray) {
this.headerArray = headerArray;
}
}
}