Java 以最快和优化的方式读取xml
我有下面这个XML文件Java 以最快和优化的方式读取xml,java,xml,Java,Xml,我有下面这个XML文件 <book> <person> <first>Kiran</first> <last>Pai</last> <age>22</age> </person> <person> <first>Bill</first> <last>Gates</last> <age>46<
<book>
<person>
<first>Kiran</first>
<last>Pai</last>
<age>22</age>
</person>
<person>
<first>Bill</first>
<last>Gates</last>
<age>46</age>
</person>
<person>
<first>Steve</first>
<last>Jobs</last>
<age>40</age>
</person>
</book>
现在我的问题是,请告知是否有其他方法可以最快地读取此xml,我正在寻找最快的方法,请告知 Stax示例
输出:
如果表演对你来说很重要,你应该选择(http://en.wikipedia.org/wiki/StAX)对 使用
DOM
,在第一次将XML
文件解析为对象模型时,您可以询问它。所以对你来说,有两个过程
使用SAX
,在解析过程中会调用一些回调(startDocument
,endElement
…),SAX
基于事件或推送模型
使用StAX
,您可以控制解析。将光标从一个图元移动到另一个图元。这是一个拉力模型
在一个包含32910000人的文件中,我将我使用SAX
的版本与使用StAX
的(Blaise Doughan的)过度回答进行比较。我删除了所有的System.out.println
指令。我的程序花了106秒读取所有文件,另一个花了94秒。
我认为SAX
较慢,因为所有回调
都会被调用,即使它们什么都不做(推模型),而使用StAX时,光标只会在“interresting”元素(pull模型)上移动
例如,java 7:
import java.io.File;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class ReadAndPrintXMLFileWithSax {
public static void main(String[] args) throws Exception {
SAXParserFactory fabrique = SAXParserFactory.newInstance();
SAXParser parser = fabrique.newSAXParser();
File file = new File("book.xml");
BookHandler handler = new BookHandler();
parser.parse(file, handler);
}
public static class BookHandler extends DefaultHandler {
private int count = 0;
private StringBuilder buffer;
@Override
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException {
switch (qName) {
case "person":
count++;
break;
case "first":
buffer = new StringBuilder("First Name : ");
break;
case "last":
buffer = new StringBuilder("Last Name : ");
break;
case "age":
buffer = new StringBuilder("Age : ");
break;
}
}
@Override
public void characters(char[] ch, int start, int length)
throws SAXException {
String content = new String(ch, start, length);
if (buffer != null)
buffer.append(content);
}
@Override
public void endElement(String uri, String localName, String qName)
throws SAXException {
switch (qName) {
case "first":
case "last":
case "age":
System.out.println(buffer.toString());
break;
}
}
@Override
public void endDocument() throws SAXException {
System.out.println(count + " persons");
}
}
}
使用下面的
ReadAndPrintXMLFileWithSAX
,与StAX方法中的ReadAndPrintXMLFileWithSAX
相比,速度更快。我的测试包括在JDK1.7.0_07上为Mac运行两个示例代码500000次
ReadAndPrintXMLFileWithStAX: 103 seconds
ReadAndPrintXMLFileWithSAX: 125 seconds
读取并打印XMLFileWithTax(使用Java SE 7)
下面是一个更优化的StAX(JSR-173)示例,它使用XMLStreamReader
而不是XMLEventReader
import java.io.FileInputStream;
import java.io.InputStream;
import javax.xml.stream.*;
public class ReadAndPrintXMLFileWithStAX {
public static void main(String argv[]) throws Exception {
XMLInputFactory inputFactory = XMLInputFactory.newInstance();
InputStream in = new FileInputStream("book.xml");
XMLStreamReader streamReader = inputFactory.createXMLStreamReader(in);
streamReader.nextTag(); // Advance to "book" element
streamReader.nextTag(); // Advance to "person" element
int persons = 0;
while (streamReader.hasNext()) {
if (streamReader.isStartElement()) {
switch (streamReader.getLocalName()) {
case "first": {
System.out.print("First Name : ");
System.out.println(streamReader.getElementText());
break;
}
case "last": {
System.out.print("Last Name : ");
System.out.println(streamReader.getElementText());
break;
}
case "age": {
System.out.print("Age : ");
System.out.println(streamReader.getElementText());
break;
}
case "person" : {
persons ++;
}
}
}
streamReader.next();
}
System.out.print(persons);
System.out.println(" persons");
}
}
输出
First Name : Kiran
Last Name : Pai
Age : 22
First Name : Bill
Last Name : Gates
Age : 46
First Name : Steve
Last Name : Jobs
Age : 40
3 persons
fast和xml通常不在一起。文本处理天生就很慢。你应该更喜欢。StAX(JSR-123)会比SAX快。@BlaiseDoughan非常感谢你,伙计,你能把我上面的程序转换成你的StAX实现吗,这样我也能详细理解。。!!首先,您应该确定程序运行缓慢的地方,而不是询问哪个是读取XML的最快方式…任何时候您想要提高性能,都应该从确定程序运行缓慢的地方开始,然后从那里开始…因此,在这个特定的程序中,什么时候运行得太慢了?我希望StAX方法会更快。下面是使用XMLStreamReader
的一种更优化的方法,在我的测试中比SAX示例更快:XMLStreamReader
比XMLEventReader
更快,请参阅:很抱歉,我不同意您对程序性能的比较。启动程序时不应使用非常小的文件,而应使用非常大的文件,否则会在jvm加载上花费太多时间。除此之外,删除控制台上的所有打印非常重要,因为它们非常昂贵。我在我的“基准”上尝试了您的代码,实际上StAX
比SAX
更快。我很惊讶,所以我试着在回答中解释这一点。请看一下并给我反馈。嘿,很高兴知道。它也干净一点。
import java.io.File;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class ReadAndPrintXMLFileWithSax {
public static void main(String[] args) throws Exception {
SAXParserFactory fabrique = SAXParserFactory.newInstance();
SAXParser parser = fabrique.newSAXParser();
File file = new File("book.xml");
BookHandler handler = new BookHandler();
parser.parse(file, handler);
}
public static class BookHandler extends DefaultHandler {
private int count = 0;
private StringBuilder buffer;
@Override
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException {
switch (qName) {
case "person":
count++;
break;
case "first":
buffer = new StringBuilder("First Name : ");
break;
case "last":
buffer = new StringBuilder("Last Name : ");
break;
case "age":
buffer = new StringBuilder("Age : ");
break;
}
}
@Override
public void characters(char[] ch, int start, int length)
throws SAXException {
String content = new String(ch, start, length);
if (buffer != null)
buffer.append(content);
}
@Override
public void endElement(String uri, String localName, String qName)
throws SAXException {
switch (qName) {
case "first":
case "last":
case "age":
System.out.println(buffer.toString());
break;
}
}
@Override
public void endDocument() throws SAXException {
System.out.println(count + " persons");
}
}
}
ReadAndPrintXMLFileWithStAX: 103 seconds
ReadAndPrintXMLFileWithSAX: 125 seconds
import java.io.FileInputStream;
import java.io.InputStream;
import javax.xml.stream.*;
public class ReadAndPrintXMLFileWithStAX {
public static void main(String argv[]) throws Exception {
XMLInputFactory inputFactory = XMLInputFactory.newInstance();
InputStream in = new FileInputStream("book.xml");
XMLStreamReader streamReader = inputFactory.createXMLStreamReader(in);
streamReader.nextTag(); // Advance to "book" element
streamReader.nextTag(); // Advance to "person" element
int persons = 0;
while (streamReader.hasNext()) {
if (streamReader.isStartElement()) {
switch (streamReader.getLocalName()) {
case "first": {
System.out.print("First Name : ");
System.out.println(streamReader.getElementText());
break;
}
case "last": {
System.out.print("Last Name : ");
System.out.println(streamReader.getElementText());
break;
}
case "age": {
System.out.print("Age : ");
System.out.println(streamReader.getElementText());
break;
}
case "person" : {
persons ++;
}
}
}
streamReader.next();
}
System.out.print(persons);
System.out.println(" persons");
}
}
First Name : Kiran
Last Name : Pai
Age : 22
First Name : Bill
Last Name : Gates
Age : 46
First Name : Steve
Last Name : Jobs
Age : 40
3 persons