Java SAX解析

Question

我需要解析一个XML流.因为我只需要做一次并构建我的java对象,所以SAX看起来是自然的选择.我正在扩展DefaultHandler并实现startElement,endElement和characters方法,在我的类中有成员保存当前读取值(在characters方法中).

我做我需要的东西没有问题,但我的代码变得非常复杂,我确信没有理由这样做,我可以做不同的事情.我的XML结构是这样的:

<players>
  <player>
    <id></id>
    <name></name>
    <teams total="2">
      <team>
        <id></id>
        <name></name>
        <start-date>
          <year>2009</year>
          <month>9</month>
        </start-date>
        <is-current>true</is-current>
      </team>
      <team>
        <id></id>
        <name></name>
        <start-date>
          <year>2007</year>
          <month>11</month>
        </start-date>
        <end-date>
          <year>2009</year>
          <month>7</month>
        </end-date>
      </team>
    </teams>
  </player>
</players>

当我意识到在文件的几个区域中使用相同的标记名称时,我的问题就出现了.例如,玩家和团队都存在id和name.我想创建我的java类Player和Team的实例.在解析时,我保留了布尔标志,告诉我我是否在团队部分,以便在endElement中我知道该名称是团队的名称,而不是玩家的名字等等.

这是我的代码的样子:

public class MyParser extends DefaultHandler {

    private String currentValue;
    private boolean inTeamsSection = false;
    private Player player;
    private Team team;
    private List<Team> teams;

    public void characters(char[] ch, int start, int length) throws SAXException {
        currentValue = new String(ch, start, length);
    }

    public void startElement(String uri, String localName, String name, Attributes attributes) throws SAXException {
        if(name.equals("player")){
            player = new Player();
        }
        if (name.equals("teams")) {
            inTeamsSection = true;
            teams = new ArrayList<Team>();
        }
        if (name.equals("team")){
            team = new Team();
        }
    }   

    public void endElement(String uri, String localName, String name) throws SAXException {
        if (name.equals("id")) {
            if(inTeamsSection){
                team.setId(currentValue);
            }
            else{
                player.setId(currentValue);
            }
        }
        if (name.equals("name")){
            if(inTeamsSection){
                team.setName(currentValue);
            }
            else{
                player.setName(currentValue);
            }
        }
        if (name.equals("team")){
            teams.add(team);
        }
        if (name.equals("teams")){
            player.setTeams(teams);
            inTeamsSection = false;
        }
    }
}

因为在我的真实场景中,除了团队之外我还有更多的节点,并且这些节点也有像name和id这样的标签,我发现自己弄乱了几个类似于inTeamsSection的布尔值,而且我的endElement方法变得冗长而且复杂很多条件.

我该怎么办？我怎么知道名称标签属于什么？

谢谢!

Answer 1

编写SAX解析器时有一个巧妙的技巧:允许ContentHandler在解析时更改 XMLReader.这允许将不同元素的解析逻辑分成多个类,这使得解析更加模块化和可重用.当一个处理程序看到其结束元素时,它会切换回其父元素.您实施的处理程序数量将留给您.代码如下所示:

public class RootHandler extends DefaultHandler {
    private XMLReader reader;
    private List<Team> teams;

    public RootHandler(XMLReader reader) {
        this.reader = reader;
        this.teams = new LinkedList<Team>();
    }

    public void startElement(String uri, String localName, String name, Attributes attributes) throws SAXException {
        if (name.equals("team")) {
            // Switch handler to parse the team element
            reader.setContentHandler(new TeamHandler(reader, this));
        }
    }
}

public class TeamHandler extends DefaultHandler {
    private XMLReader reader;
    private RootHandler parent;
    private Team team;
    private StringBuilder content;

    public TeamHandler(XMLReader reader, RootHandler parent) {
        this.reader = reader;
        this.parent = parent;
        this.content = new StringBuilder();
        this.team = new Team();
    }

    // characters can be called multiple times per element so aggregate the content in a StringBuilder
    public void characters(char[] ch, int start, int length) throws SAXException {
        content.append(ch, start, length);
    }

    public void startElement(String uri, String localName, String name, Attributes attributes) throws SAXException {
        content.setLength(0);
    }

    public void endElement(String uri, String localName, String name) throws SAXException {
        if (name.equals("name")) {
            team.setName(content.toString());
        } else if (name.equals("team")) {
            parent.addTeam(team);
            // Switch handler back to our parent
            reader.setContentHandler(parent);
        }
    }
}