替换字符串中某些参数形成新的字符串

http://blog.csdn.net/preferme/article/details/5340793

package houlei.java.util;

import java.util.Map;
import java.lang.StringBuilder;

/**
 * <strong>可替换参数变量的字符串类。</strong>参数的形式为：${参数}<p/>
 * 例如：字符串 "This is a ${SomeThing}." 可替换的部分是：${SomeThing}。其中，SomeThing即为参数。<br/>
 * 如果要将${SomeThing}替换为字符串"Demo"（也就是说替换后的字符串是："This is a Demo."），
 * 我们可以将SomeThing和Demo组成键值对放入Map中进行转换。<p/>
 * 代码示例：<br/>
 * <pre>{@code
 *   String demoStr = "This is a ${SomeThing}.";
 *   DynamicString ds = new DynamicString(demoStr);
 *   Map<String,String> param = new java.util.HashMap<String,String>(4);
 *   param.put("SomeThing", "Demo");
 *   System.out.println(ds.convert(param));
 * }</pre>
 * <strong>注意：反斜杠'/'是转义字符，活用可处理常见问题。</strong>
 * <P>该类创建于 2010-3-3 上午01:06:26
 * @version 1.0.0
 * @author 侯磊
 */
public class DynamicString {

	private String dynStr;
	private DynamicPattern header;
	private DynamicPattern tail;

	static abstract class DynamicPattern {
		DynamicPattern next;
		public abstract Object subConvert(Map<String,?> pattern);
	}

	static class StringPattern extends DynamicPattern {
		private String pattern;

		public StringPattern(StringBuilder buff, int start, int end) {
			this.pattern = buff.substring(start, end);
		}
		@Override
		public Object subConvert(Map<String,? extends Object> map) {
			return pattern;
		}
	}

	static class MappedPattern extends DynamicPattern {
		private String key;

		public MappedPattern(StringBuilder buff, int start, int end) {
			this.key = buff.substring(start, end);
		}
		@Override
		public Object subConvert(Map<String,? extends Object> param) {
			if(param.get(key)==null){
				throw new IllegalArgumentException("所传入的Map中，不含有参数："+key);
			}
			return param.get(key);
		}
	}

	/**可替换参数变量的字符串类。该类适用于多个参数的情况。
	 * @param dynStr 模板字符串。
	 */
	public DynamicString(String dynStr) {
		this.dynStr = dynStr;
		init();
	}

	/**
	 * 生成中间模板，转义字符也要考虑在内。
	 */
	private void init() {
		header = tail = null;
		StringBuilder buff = new StringBuilder(dynStr);
		int start = 0, ptr = 0;
		boolean noMatching = true;
		for (ptr = start; ptr < buff.length(); ptr++) {
			if(buff.charAt(ptr)=='$' && buff.charAt(ptr+1)=='{'){
				if(ptr>0 && buff.charAt(ptr-1)=='//'){
					buff.deleteCharAt(ptr---1);
					if(ptr>1 && buff.charAt(ptr-1)=='//' && buff.charAt(ptr-2)=='//'){
						buff.deleteCharAt(ptr---1);continue;
					}
					if(!(ptr>0 && buff.charAt(ptr-1)=='//'))
					continue;
				}
				noMatching=false;
		        StringPattern sp = new StringPattern(buff, start, ptr);
		        appendPattern(sp);
		        start = ptr+2;
		        for (ptr += 2; ptr < buff.length(); ptr++) {
		        	if (buff.charAt(ptr) == '}') {
		        		if(buff.charAt(ptr-1)=='//'){
		        			buff.deleteCharAt(ptr---1);
		        			if(buff.charAt(ptr-1)!='//')
		        			continue;
		        		}
		        		MappedPattern mp = new MappedPattern(buff, start, ptr);
		        		appendPattern(mp);
		        		noMatching=true;
		        		start = ++ptr;break;
		        	}
		        }
			}
		}
		if (noMatching && ptr <= buff.length())
			appendPattern(new StringPattern(buff, start, ptr));
	}

	private DynamicString appendPattern(DynamicPattern pattern) {
		if (header == null) {
			header = pattern;
			tail = header;
		} else {
			tail.next = pattern;
			tail = pattern;
		}
		return this;
	}

	/**传入参数变量，得到替换后的结果。
	 * @param param 将替换的参数及变量以键值对的形式存放到Map对象中。
	 * @return  返回替换回的结果。
	 * @exception IllegalArgumentException 当待替换的参数不在Map对象中时，抛出该异常。
	 */
	public String convert(Map<String,? extends Object> param) {
		if (header == null)
			return null;
		DynamicPattern ptr = header;
		StringBuilder sb = new StringBuilder();
		while (ptr != null) {
			sb.append(ptr.subConvert(param));
			ptr = ptr.next;
		}
		return sb.toString();
	}

	/**
	 * @see #convert(Map)
	 */
	public String convert(String key,String value){
		Map<String,String> param = new java.util.HashMap<String,String>(2);
		param.put(key, value);
		return convert(param);
	}
}

真是相当有用啊