恩恩是的，挺奇妙的吧，嘿嘿，可以一起交流 一起学习

如果你是想自己输入字符串加进去的话，把他toCharArray再用之前的方法加进去就好了，区间就是0到length-1

不会呀，代码错了？

既然是空值<name/>和<name></name>是一样的，没有必要纠结这个吧

我个人操作是在导入的XML文件中读取的数据,编辑数据也只是在这个文件中进行操作.

public void SAXWriteXml() {
		List<Book> bookList = SAXReadXml();
		// 1 创建SAXTransformerFactory类的对象
		SAXTransformerFactory stff = (SAXTransformerFactory) SAXTransformerFactory
				.newInstance();
		try {
			// 2通过SAXTransformerFactory对象创建一个TransformerHandler对象
			TransformerHandler handler = stff.newTransformerHandler();
			// 3通过handler创建Transformer对象
			Transformer tf = handler.getTransformer();
			// 4通过Transformer对象对生成的xml文件进行设置
			tf.setOutputProperty(OutputKeys.ENCODING, "utf-8");
			tf.setOutputProperty(OutputKeys.INDENT, "yes");
			// 5创建一个Result对象
			File file = new File("source/shuji.xml");
			if (!file.exists()) {
				file.createNewFile();
			}
			// 6创建Result对象,result与handler关联
			Result result = new StreamResult(new FileOutputStream(file));
			handler.setResult(result);
			// 7利用Handler对象进行xml文件内容的填充
			// 打开document文档
			handler.startDocument();
			AttributesImpl atts = new AttributesImpl();
			handler.startElement("", "", "bookstore", atts);
			for (Book book : bookList) {
				atts.clear();
				atts.addAttribute("", "", "id", "", book.getId());
				handler.startElement("", "", "book", atts);
				atts.clear();
				// 创建name节点
				if ((book.getName() != null)
						&& !book.getName().trim().equals("")) {
					atts.clear();
					System.out.println("+++++name+++++");
					handler.startElement("", "", "name", atts);//这里没有执行
					System.out.println("+++++name+++++");
					handler.characters(book.getName().toCharArray(), 0, book
							.getName().length());
					handler.endElement("", "", "name");
					
				}
				if (!book.getAuthor().trim().equals("")
						&& (book.getAuthor() != null)) {
					atts.clear();
					System.out.println("+++++author+++++");
					handler.startElement("", "", "author", atts);
					handler.characters(book.getAuthor().toCharArray(), 0, book
							.getAuthor().length());
					handler.endElement("", "", "author");
				}
				if (!book.getYear().trim().equals("")
						&& (book.getYear() != null)) {
					atts.clear();
					handler.startElement("", "", "year", atts);
					handler.characters(book.getYear().toCharArray(), 0, book
							.getYear().length());
					handler.endElement("", "", "year");
				}
				if (!book.getPrice().trim().equals("")
						&& (book.getPrice() != null)) {
					atts.clear();
					handler.startElement("", "", "price", atts);
					handler.characters(book.getPrice().toCharArray(), 0, book
							.getPrice().length());
					handler.endElement("", "", "price");
				}
				if (!book.getLanguage().trim().equals("")
						&& (book.getLanguage() != null)) {
					atts.clear();
					handler.startElement("", "", "language", atts);
					handler.characters(book.getLanguage().toCharArray(), 0,
							book.getLanguage().length());
					handler.endElement("", "", "language");
				}

				handler.endElement("", "", "book");
			}

			handler.endElement("", "", "bookstore");
			// 关闭document
			handler.endDocument();
		} catch (TransformerConfigurationException e) {
			e.printStackTrace();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}
	}
	//异常
	Exception in thread "main" java.lang.NullPointerException
	at com.sun.org.apache.xml.internal.serializer.ToStream.writeAttrString(ToStream.java:1967)
	at com.sun.org.apache.xml.internal.serializer.ToStream.processAttributes(ToStream.java:1947)
	at com.sun.org.apache.xml.internal.serializer.ToStream.closeStartTag(ToStream.java:2443)
	at com.sun.org.apache.xml.internal.serializer.ToStream.startElement(ToStream.java:1783)
	at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.startElement(ToUnknownStream.java:548)
	at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerHandlerImpl.startElement(TransformerHandlerImpl.java:267)
	at com.live.imooc.test.SAXTest.SAXWriteXml(SAXTest.java:70)
	at com.live.imooc.test.SAXTest.main(SAXTest.java:31)

上面是我写的函数；报的错误是空指针异常。

我之前也出现过这个问题;你是不是在for语句里面释放了book = null;然后没有new再调用就会出现这个问题.

去除空格与换行符

package com.imooc.test;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import javax.xml.parsers.ParserConfigurationException;
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.TransformerConfigurationException;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TransformerHandler;
import javax.xml.transform.stream.StreamResult;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.AttributesImpl;
public class SaxTest {
 
  public  ArrayList<Book> xmlParse(){
   SAXParserFactory factory=SAXParserFactory.newInstance();
   HandlerTest handler=null;  
   try {
    SAXParser parser=factory.newSAXParser();
     handler=new HandlerTest();
       parser.parse("f:\\books.xml",handler); 
    /*  System.out.println("----共有"+handler.getBookList().size()+"本书-----"); 
      for(Book book1:handler.getBookList()){//遍历booList中的内容
       System.out.println("===========开始==========");
       System.out.println(book1.getID());
       System.out.println(book1.getName());
       System.out.println(book1.getAuthor());
       System.out.println(book1.getYear());
       System.out.println(book1.getPrice());
       System.out.println(book1.getLanguage());
       System.out.println("===========结束==========");
      }*/
   
   } catch (ParserConfigurationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (SAXException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IOException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }
         return handler.getBookList();
        }
   
  public void xmlCreate(){
   ArrayList<Book> booklist=xmlParse();
  SAXTransformerFactory tff=(SAXTransformerFactory) SAXTransformerFactory.newInstance();
  try {
   TransformerHandler handler=tff.newTransformerHandler();
   Transformer tf=handler.getTransformer();
   tf.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
   tf.setOutputProperty(OutputKeys.INDENT, "yes");
   File f=new File("src/res/newbooks.xml");
   if(!f.exists()){
       f.createNewFile();
   }
   Result result=new StreamResult(new FileOutputStream(f));
   handler.setResult(result);
   handler.startDocument();
   AttributesImpl attr=new AttributesImpl();
   handler.startElement("","","bookStore",attr);
   for(Book book:booklist){
   attr.clear();
   attr.addAttribute("", "", "id","",book.getID());
         handler.startElement("","","book",attr);
        
         if(book.getName()!=null&&!book.getName().trim().equals("")){
            attr.clear();
            handler.startElement("", "","name", attr); 
            handler.characters(book.getName().toCharArray(), 0,book.getName().length());
             handler.endElement("","","name");
         }
        
         
        
         if(!book.getAuthor().equals(null)&&!book.getAuthor().trim().equals("")){
           attr.clear();
              handler.startElement("", "","author", attr);
              handler.characters(book.getAuthor().toCharArray(), 0,book.getAuthor().length());
               handler.endElement("","","author");
         }
            
           if(book.getYear()!=null&&!book.getYear().trim().equals("")){
          attr.clear();
          handler.startElement("", "","year", attr);          
             handler.characters(book.getYear().toCharArray(), 0,book.getYear().length());
             handler.endElement("","","year");         
         }
            if(book.getLanguage()!=null&&!book.getLanguage().trim().equals("")){
          attr.clear();
          handler.startElement("", "","language", attr);          
             handler.characters(book.getLanguage().toCharArray(), 0,book.getLanguage().length());
             handler.endElement("","","language");         
         }
            if(book.getPrice()!=null&&!book.getPrice().trim().equals("")){
          attr.clear();
          handler.startElement("", "","price", attr);          
             handler.characters(book.getPrice().toCharArray(), 0,book.getPrice().length());
             handler.endElement("","","price");         
         }
    
            handler.endElement("","","book");
   }
   handler.endElement("","","bookStore");
   handler.endDocument();
   
   
  } catch (TransformerConfigurationException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
 }catch (IOException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
 }catch (SAXException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } 
  }  
 public static void main(String[] args) {
  // TODO Auto-generated method stub
 SaxTest test=new SaxTest();
 test.xmlCreate();
 }
}

代码的位置放置不对

找到了，多加了一句handler.endElement

获取的某个对象为null时，调用该对象的方法就会报空指针，检查一下代码，看哪个对象为空。