Wellformedness and Validity of a XML file

bodong_chen — Mon, 03 Apr 2006 09:41:00 GMT

在一个有关Jdom的讨论中提到：

Elliotte Rusty Harold: XML documents must be well-formed. There are, depending on how you count, anywhere from a hundred to several thousand different rules. These "well-formedness" rules are the minimum requirements for an XML document. The rules cover things like what characters are allowed in element names: The letter 'a' is OK. The letter omega is OK. The asterisk character is not OK. White space is not OK. The rules say that every start-tag has to have a matching end-tag. Elements can nest, but they cannot overlap. Processing instructions have the form <, ?, a target, white space, the data, ?, and a >. Comments cannot contain a double hyphen. There are many such rules governing well-formedness of XML documents.

Validity talks about which elements and attributes are allowed where. Well-formedness only talks about the structure of any XML document, irrespective of what the names are. Validity says, we're only going to allow these elements with these names in these positions. Validity is not required. Well-formedness is.

JDOM, and for that matter DOM, allows you to create malformed documents. They do not check everything they can possibly check. For instance, they do not currently check that the text content of a text node does not contain the null character, which is completely illegal in an XML document.

这是发生在2003年的讨论:http://www.artima.com/intv/jdom2.html。

现在，使用JDOM可以完成这两件事：
1. 验证XML文件的Wellformedness:
The build() method of SAXBuilder throws an IOException if an I/O error such as a broken socket prevents the document from being completely read. It throws a JDOMException if the document is malformed. This is the generic superclass for most things that can go wrong while working with JDOM other than I/O errors.
Example:

import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;
import java.io.IOException;

public class JDOMChecker {

  public static void main(String[] args) {

    if (args.length == 0) {
      System.out.println("Usage: java JDOMChecker URL");
      return;
    }

    SAXBuilder builder = new SAXBuilder();

    // command line should offer URIs or file names
    try {
      builder.build(args[0]);
      // If there are no well-formedness errors,
      // then no exception is thrown
      System.out.println(args[0] + " is well-formed.");
    }
    // indicates a well-formedness error
    catch (JDOMException e) {
      System.out.println(args[0] + " is not well-formed.");
      System.out.println(e.getMessage());
    }
    catch (IOException e) {
      System.out.println("Could not check " + args[0]);
      System.out.println(" because " + e.getMessage());
    }
  }
}

2. 验证XML文件的Validity:
SAXBuilder only checks documents for well-formedness, not validity. If you want to validate as well, then pass the boolean true to the SAXBuilder() constructor. Then any validity errors will also cause JDOMExceptions.

import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;
import java.io.IOException;

public class JDOMValidator {

  public static void main(String[] args) {

    if (args.length == 0) {
      System.out.println("Usage: java JDOMValidator URL");
      return;
    }

    SAXBuilder builder = new SAXBuilder(true);
                                    //  ^^^^
                                    // Turn on validation

    // command line should offer URIs or file names
    try {
      builder.build(args[0]);
      // If there are no well-formedness or validity errors,
      // then no exception is thrown.
      System.out.println(args[0] + " is valid.");
    }
    // indicates a well-formedness or validity error
    catch (JDOMException e) {
      System.out.println(args[0] + " is not valid.");
      System.out.println(e.getMessage());
    }
    catch (IOException e) {
      System.out.println("Could not check " + args[0]);
      System.out.println(" because " + e.getMessage());
    }
  }
}

参考文献：http://www.ibiblio.org/xml/books/xmljava/chapters/ch14s07.html

bodong_chen 2006-04-03 17:41 发表评论

使用JDOM读写XML的方法

bodong_chen — Fri, 11 Nov 2005 06:54:00 GMT

1. 读
读XML有多种方法．最基本的方法如下：
<1>用SAXBuilder类构造一个实例，并创建一个文件：
// Build the document with SAX and Xerces, no validation
SAXBuilder builder = new SAXBuilder();
// Create the document
Document doc = builder.build(new File("d:\\data.xml"));
<2>调用Element类中的众多方法获取信息：
一下是在JSP中递归获取XML文件中的元素的基本信息的函数：
public void printChildren(Element parentElement,JspWriter out) throws java.io.IOException
{
    List children = parentElement.getChildren();
if(children==null || children.size()==0)
  return;
for(int i=0 ; i {
  Element aChild = (Element)children.get(i);
  out.print(aChild.getName()+":");
  out.print(aChild.getText()+"
");
  printChildren(aChild,out);
}
}
上例用到了getChildren()，getName()，getText()三个方法。更多的方法参见doc文档。

2. 写
<1> 创建文档
Document document=new Document(new Element("name of the root Element"));//调用的是new Document(Element rootElement)的构造函数。
说明:
Document类：Document defines behavior for an XML Document，定义了文件级的各种操作。
Element类：Attribute defines behavior for an XML attribute。

<2>逐个逐层写入element
Element chileElement=new Element("name of a child Element"); //创建元素生成JDOM树
document.getRootElement().addContent(chileElement);
说明：
这个过程主要调用了Element类的addContent(Element anElement)方法。

<3>输出成XML文件
XMLOutputter outp = new XMLOutputter();
outp.output(document, new FileOutputStream("d:\\data.xml")); //输出XML文档
说明：
这种方法得到的XML的格式很不好看，要得到层次明显的XML，可采用如下方法：
a. XMLOutputter outp = new XMLOutputter(Format.getPrettyFormat()); //利用Format类

b. XMLOutputter outputter = new XMLOutputter("", false);//第一个参数代表缩进方式，第二个参数代表是否换行。

c. XMLOutputter outp = new XMLOutputter("",true,"GB2312");//支持中文的带换行和缩进的格式
outp.setTextTrim(true);
outp.output(doc, System.out);

附：读写XML的例程：
1. 读：jdomreadxml.jsp
<%@page contentType="text/html;charset=GBK"%>
<%@page import="java.util.List,java.sql.*,java.io.*,org.jdom.*,org.jdom.output.*,org.jdom.input.*"%>
<%!
public void printChildren(Element parentElement,JspWriter out) throws java.io.IOException
{
    List children = parentElement.getChildren();
if(children==null || children.size()==0)
  return;
for(int i=0 ; i {
  Element aChild = (Element)children.get(i);
  out.print(aChild.getName()+":");
  out.print(aChild.getText()+"
");
  printChildren(aChild,out);
}
}
%>

用JDOM实现数据库到XML的转换

<%
// Build the document with SAX and Xerces, no validation
SAXBuilder builder = new SAXBuilder();
// Create the document
Document doc = builder.build(new File("d:\\data.xml"));
Element rootElement = doc.getRootElement();
out.print("Elements go here:");
out.print("
");
printChildren(rootElement,out);
%>

2. 写：（从Access数据库中获取字段并写入）
jdomdbtoxml.jsp
<%@page contentType="text/html;charset=GBK"%>
<%@page import="java.sql.*,java.io.*,org.jdom.*,org.jdom.output.*"%>

用JDOM实现数据库到XML的转换

<%
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
java.sql.Connection conn = java.sql.DriverManager.getConnection("jdbc:odbc:students");
java.sql.Statement stmt = conn.createStatement();
String sql="select * from student";   //定义查询的SQL语句
ResultSet rs=stmt.executeQuery(sql);   //执行查询
Document document=new Document(new Element("student_list"));//创建文档
java.sql.ResultSetMetaData rsmd = rs.getMetaData(); //获取字段名
int numberOfColumns = rsmd.getColumnCount(); //获取字段数
int i=0;
while(rs.next()){ //将查询结果取出
    Element element0=new Element("student"); //创建元素生成JDOM树
    document.getRootElement().addContent(element0);
    for (i=1; i<=numberOfColumns;i++)
{
  String date=new String(rs.getString(i)); //代码转换
  Element element=new Element(rsmd.getColumnName(i)).setText(date);
  element0.addContent(element);
}
}
rs.close();                            //关闭结果集
stmt.close();                       //关闭statement
conn.close();                      //关闭连接

XMLOutputter outp = new XMLOutputter(Format.getPrettyFormat());
outp.output(document, new FileOutputStream("d:\\data.xml")); //输出XML文档
out.print("XML 文档生成完毕！");
%>

bodong_chen 2005-11-11 14:54 发表评论

BlogJava-bodong_chen-随笔分类-XML

Wellformedness and Validity of a XML file

使用JDOM读写XML的方法