接下来，就该介绍操作过程了，我们先为解析器定义一个BookParser接口，每种类型的解析器需要实现此接口。BookParser.java代码如下：
package com.scott.xml.parser;
import java.io.InputStream;
import java.util.List;
import com.scott.xml.model.Book;
public interface BookParser {
/**
* 解析输入流 得到Book对象集合
* @param is
* @return
* @throws Exception
*/
public List<Book> parse(InputStream is) throws Exception;
/**
* 序列化Book对象集合 得到XML形式的字符串
* @param books
* @return
* @throws Exception
*/
public String serialize(List<Book> books) throws Exception;
}
好了，我们就该一个一个的实现该接口，完成我们的解析过程。
使用SAX解析器：
SaxBookParser.java代码如下：
package com.scott.xml.parser;
import java.io.InputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TransformerHandler;
import javax.xml.transform.stream.StreamResult;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.helpers.DefaultHandler;
import com.scott.xml.model.Book;
public class SaxBookParser implements BookParser {
@Override
public List<Book> parse(InputStream is) throws Exception {
SAXParserFactory factory = SAXParserFactory.newInstance(); //取得SAXParserFactory实例
SAXParser parser = factory.newSAXParser(); //从factory获取SAXParser实例
MyHandler handler = new MyHandler(); //实例化自定义Handler
parser.parse(is, handler); //根据自定义Handler规则解析输入流
return handler.getBooks();
}
@Override
public String serialize(List<Book> books) throws Exception {
SAXTransformerFactory factory = (SAXTransformerFactory) TransformerFactory.newInstance();//取得SAXTransformerFactory实例
TransformerHandler handler = factory.newTransformerHandler(); //从factory获取TransformerHandler实例
Transformer transformer = handler.getTransformer(); //从handler获取Transformer实例
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8"); // 设置输出采用的编码方式
transformer.setOutputProperty(OutputKeys.INDENT, "yes"); // 是否自动添加额外的空白
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); // 是否忽略XML声明
StringWriter writer = new StringWriter();
Result result = new StreamResult(writer);
handler.setResult(result);
String uri = ""; //代表命名空间的URI 当URI无值时 须置为空字符串
String localName = ""; //命名空间的本地名称(不包含前缀) 当没有进行命名空间处理时 须置为空字符串
handler.startDocument();
handler.startElement(uri, localName, "books", null);
AttributesImpl attrs = new AttributesImpl(); //负责存放元素的属性信息
char[] ch = null;
for (Book book : books) {
attrs.clear(); //清空属性列表
attrs.addAttribute(uri, localName, "id", "string", String.valueOf(book.getId()));//添加一个名为id的属性(type影响不大,这里设为string)
handler.startElement(uri, localName, "book", attrs); //开始一个book元素 关联上面设定的id属性
handler.startElement(uri, localName, "name", null); //开始一个name元素 没有属性
ch = String.valueOf(book.getName()).toCharArray();
handler.characters(ch, 0, ch.length); //设置name元素的文本节点
handler.endElement(uri, localName, "name");
handler.startElement(uri, localName, "price", null);//开始一个price元素 没有属性
ch = String.valueOf(book.getPrice()).toCharArray();
handler.characters(ch, 0, ch.length); //设置price元素的文本节点
handler.endElement(uri, localName, "price");
handler.endElement(uri, localName, "book");
}
handler.endElement(uri, localName, "books");
handler.endDocument();
return writer.toString();
}
//需要重写DefaultHandler的方法
private class MyHandler extends DefaultHandler {
private List<Book> books;
private Book book;
private StringBuilder builder;
//返回解析后得到的Book对象集合
public List<Book> getBooks() {
return books;
}
@Override
public void startDocument() throws SAXException {
super.startDocument();
books = new ArrayList<Book>();
builder = new StringBuilder();
}
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
super.startElement(uri, localName, qName, attributes);
if (localName.equals("book")) {
book = new Book();
}
builder.setLength(0); //将字符长度设置为0 以便重新开始读取元素内的字符节点
}
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
super.characters(ch, start, length);
builder.append(ch, start, length); //将读取的字符数组追加到builder中
}
@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
super.endElement(uri, localName, qName);
if (localName.equals("id")) {
book.setId(Integer.parseInt(builder.toString()));
} else if (localName.equals("name")) {
book.setName(builder.toString());
} else if (localName.equals("price")) {
book.setPrice(Float.parseFloat(builder.toString()));
} else if (localName.equals("book")) {
books.add(book);
}
}
}
}
