Chapter 2 - Jetty读取配置文件和Loader (2)

1. XmlConfiguration的value方法

读取某个节点的值，并进行相应处理：修剪空字符串，解析并拼接结果

private Object value(Object obj, XmlParser.Node node) throws Exception
    {
        Object value = null;

        // Get the type
        String type = node.getAttribute("type");

        // Try a ref lookup
        String ref = node.getAttribute("ref");
        if (ref != null)
        {
            value = _idMap.get(ref);
        }
        else
        {
            // handle trivial case
            if (node.size() == 0)
            {
                if ("String".equals(type)) return "";
                return null;
            }

            // Trim values
            int first = 0;
            int last = node.size() - 1;

            // Handle default trim type
            if (type == null || !"String".equals(type))
            {
                // Skip leading white
                Object item = null;
                while (first <= last)
                {
                    item = node.get(first);
                    if (!(item instanceof String)) break;
                    item = ((String) item).trim();
                    if (((String) item).length() > 0) break;
                    first++;
                }

                // Skip trailing white
                while (first < last)
                {
                    item = node.get(last);
                    if (!(item instanceof String)) break;
                    item = ((String) item).trim();
                    if (((String) item).length() > 0) break;
                    last--;
                }

                // All white, so return null
                if (first > last) return null;
            }

            if (first == last)
                //  Single Item value
                value = itemValue(obj, node.get(first));
            else
            {
                // Get the multiple items as a single string
                StringBuffer buf = new StringBuffer();
                synchronized (buf)
                {
                    for (int i = first; i <= last; i++)
                    {
                        Object item = node.get(i);
                        buf.append(itemValue(obj, item));
                    }
                    value = buf.toString();
                }
            }
        }

        // Untyped or unknown
        if (value == null)
        {
            if ("String".equals(type)) return "";
            return null;
        }

        // Try to type the object
        if (type == null)
        {
            if (value != null && value instanceof String) return ((String) value).trim();
            return value;
        }

        if ("String".equals(type) || "java.lang.String".equals(type)) return value.toString();

        Class pClass = TypeUtil.fromName(type);
        if (pClass != null) return TypeUtil.valueOf(pClass, value.toString());

        if ("URL".equals(type) || "java.net.URL".equals(type))
        {
            if (value instanceof URL) return value;
            try
            {
                return new URL(value.toString());
            }
            catch (MalformedURLException e)
            {
                throw new InvocationTargetException(e);
            }
        }

        if ("InetAddress".equals(type) || "java.net.InetAddress".equals(type))
        {
            if (value instanceof InetAddress) return value;
            try
            {
                return InetAddress.getByName(value.toString());
            }
            catch (UnknownHostException e)
            {
                throw new InvocationTargetException(e);
            }
        }

        throw new IllegalStateException("Unknown type " + type);
    }

2. XmlConfiguration的itemValue方法

读取单个节点的值，如果item是String类型，直接返回
如果是其它的tag，还需要调用对应的处理方法

private Object itemValue(Object obj, Object item) throws Exception
    {
        // String value
        if (item instanceof String) return item;

        XmlParser.Node node = (XmlParser.Node) item;
        String tag = node.getTag();
        if ("Call".equals(tag)) return call(obj, node);
        if ("Get".equals(tag)) return get(obj, node);
        if ("New".equals(tag)) return newObj(obj, node);
        if ("Ref".equals(tag)) return refObj(obj, node);
        if ("Array".equals(tag)) return newArray(obj, node);
        if ("Map".equals(tag)) return newMap(obj, node);
        if ("Property".equals(tag)) return propertyObj(obj,node);

        if ("SystemProperty".equals(tag))
        {
            String name = node.getAttribute("name");
            String defaultValue = node.getAttribute("default");
            return System.getProperty(name, defaultValue);
        }
        
        Log.warn("Unknown value tag: " + node, new Throwable());
        return null;
    }