Android网络-DOM方式解析Xml数据

一. 前言

1. DOM解析

DOM 解析是把文件一次性加载到内存里，生成一个树状结构，在内存中对树状节点进行修改或添加节点。所以，这种方法的缺点是消耗的内存太大。

2. 常用的方法

DocumentBuilder抽象类
/**
 * Parse the content of the given <code>InputStream</code> as an XML
 * document and return a new DOM {@link Document} object.
 * An <code>IllegalArgumentException</code> is thrown if the
 * <code>InputStream</code> is null.
 *
 * @param is InputStream containing the content to be parsed.
 * @return <code>Document</code> result of parsing the
 *  <code>InputStream</code>
 * @exception IOException If any IO errors occur.
 * @exception SAXException If any parse errors occur.
 * @see org.xml.sax.DocumentHandler
 */
public Document parse(InputStream is)

Document接口
/**
 * Returns a <code>NodeList</code> of all the <code>Elements</code> in
 * document order with a given tag name and are contained in the
 * document.
 * @param tagname  The name of the tag to match on. The special value "*"
 *   matches all tags. For XML, the <code>tagname</code> parameter is
 *   case-sensitive, otherwise it depends on the case-sensitivity of the
 *   markup language in use.
 * @return A new <code>NodeList</code> object containing all the matched
 *   <code>Elements</code>.
 */
public NodeList getElementsByTagName(String tagname);

NodeList接口
/**
 * Returns the <code>index</code>th item in the collection. If
 * <code>index</code> is greater than or equal to the number of nodes in
 * the list, this returns <code>null</code>.
 * @param index Index into the collection.
 * @return The node at the <code>index</code>th position in the
 *   <code>NodeList</code>, or <code>null</code> if that is not a valid
 *   index.
 */
public Node item(int index);

Node接口
/**
 * A <code>NamedNodeMap</code> containing the attributes of this node (if
 * it is an <code>Element</code>) or <code>null</code> otherwise.
 */
public NamedNodeMap getAttributes();

Node接口
/**
 * The first child of this node. If there is no such node, this returns
 * <code>null</code>.
 */
public Node getFirstChild();

Node接口
/**
 * The value of this node, depending on its type; see the table above.
 * When it is defined to be <code>null</code>, setting it has no effect,
 * including if the node is read-only.
 * @exception DOMException
 *   DOMSTRING_SIZE_ERR: Raised when it would return more characters than
 *   fit in a <code>DOMString</code> variable on the implementation
 *   platform.
 */
public String getNodeValue() throws DOMException;

二. 实际小例子

1. 待解析的Xml文件

<?xml version="1.0" encoding="utf-8"?>
<web>
    <item id="0" url="https://www.baidu.com">百度</item>
    <item id="1" url="https://www.taobao.com">淘宝</item>
    <item id="2" url="https://www.qq.com">腾讯</item>
    <item id="3" url="https://www.aili.com">阿里巴巴</item>
    <item id="4" url="https://www.taobao.com">淘宝</item>
    <item id="5" url="https://www.wechat.com">微信</item>
    <item id="6" url="https://www.timi.com">天美</item>
    <item id="7" url="https://www.guangzi.com">光子</item>
    <item id="8" url="https://www.taoken.com">字节跳动</item>
    <item id="9" url="https://www.douyin.com">抖音</item>
</web>

2. Activity中的调用

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //DOM解析
        testDOMParse();
    }

    /**
     * DOM解析
     */
    private void testDOMParse(){
        //存储解析的模型资源
        List<WebItem> webItems = new ArrayList<>();

        //临时的模型类
        WebItem webItem = null;

        try {
            //创建一个DocumentBuilder工厂类
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();

            //根据DocumentBuilder工厂类创建DocumentBuilder
            DocumentBuilder db = dbf.newDocumentBuilder();

            //使用DocumentBuilder加载xml文件
            Document document = db.parse(getResources().openRawResource(R.raw.test));

            //获取所有的item节点集合
            NodeList items = document.getElementsByTagName("item");

            //遍历每一个item节点
            for (int i = 0; i < items.getLength(); i++) {
                //初始化模型类
                webItem = new WebItem();

                //获取一个具体的item
                Node item = items.item(i);

                //获取一个item的所有属性集合
                NamedNodeMap attrs = item.getAttributes();

                //遍历item的所有属性
                for (int j = 0; j < attrs.getLength(); j++) {
                    //获取某个属性
                    Node node = attrs.item(j);
                    //获取节点属性名
                    String nodeName = node.getNodeName();
                    //获取节点属性值
                    String nodeValue = node.getNodeValue();

                    if (TextUtils.equals(nodeName,"id")){
                        webItem.setId(Integer.parseInt(nodeValue));
                    }

                    if (TextUtils.equals(nodeName,"url")){
                        webItem.setUrl(nodeValue);
                    }
                }

                //获取item的值
                String content = item.getFirstChild().getNodeValue();
                webItem.setContent(content);

                //加入集合
                webItems.add(webItem);
            }

        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        for (WebItem item : webItems) {
            //Toast.makeText(this, "id:"+item.getId()+" url:"+item.getUrl()+" content:"+item.getContent(), Toast.LENGTH_SHORT).show();
            //显示数据
            addToRootLayout((LinearLayout) findViewById(R.id.root),item);
        }
    }

    /**
     * 将WebItem显示到布局中
     * @param layout
     * @param webItem
     */
    private void addToRootLayout(LinearLayout layout, WebItem webItem){
        View inflate = LayoutInflater.from(this).inflate(R.layout.web_item_layout, null);
        TextView id_text = inflate.findViewById(R.id.id);
        TextView content_text = inflate.findViewById(R.id.content);
        TextView url_text = inflate.findViewById(R.id.url);

        id_text.setText(String.valueOf(webItem.getId()));
        content_text.setText(webItem.getContent());
        url_text.setText(webItem.getUrl());

        layout.addView(inflate);
    }
}