基于倒排索引的缓存对象索引通用解决方案 博客分类： java java倒排索引

一个给javabean列表建立倒排索引的通用类，主要可用于给缓存中的一类对象添加索引便于搜索，对于缓存中的对象实现模糊搜索是一种非常合适的方案

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class InvertedIndexGeneric<T> {
	/**
	 * 索引
	 */
	private Map<String, List<T>> invertedIndex = new HashMap<String, List<T>>();
	/**
	 * 缓存的待索引项
	 */
	private Map<String, T> invertedIndexItemsMap = new HashMap<String, T>();

	/**
	 * 主键属性的get方法
	 */
	private Method prekeyMethod;
	/**
	 * 被索引属性的get方法
	 */
	private Method indexedAttrMethod;

	private Class<T> beanClass;

	/**
	 * 
	 * @param beanList
	 *            待索引javabean列表
	 * @param targetBeanClass
	 *            待索引javabean类型
	 * @param preKeyAttr
	 *            待索引项唯一标识(主键)的javabean属性名
	 * @param indexedAttr
	 *            待索引项的附加索引的javabean属性名
	 */
	public InvertedIndexGeneric(List<T> beanList, Class<T> targetBeanClass,
			String preKeyAttr, String indexedAttr) {
		if (beanList == null || beanList.size() == 0) {
			throw new RuntimeException("待索引项为空！");
		}
		this.beanClass = targetBeanClass;
		this.prekeyMethod = this.buildAttrGetMethod(preKeyAttr);
		this.indexedAttrMethod = this.buildAttrGetMethod(indexedAttr);
		for (T invertedIndexAble : beanList) {
			invertedIndexItemsMap
					.put(this.getIndexedBeanPrekey(invertedIndexAble),
							invertedIndexAble);
		}
		this.buildInverteIndex();
	}

	/**
	 * 查询键值相关的索引项
	 * 
	 * @param key
	 *            关键字
	 * @return 键值相关的索引项
	 */
	public synchronized List<T> find(String key) {
		return invertedIndex.get(key);
	}

	/**
	 * 增加待索引项
	 * 
	 * @param item
	 *            待索引项
	 */
	public synchronized void addInvertItem(T item) {
		List<String> keys = getAllKeys(this.getIndexedAttrValue(item));
		for (int i = 0; i < keys.size(); i++) {
			String key = keys.get(i);
			List<T> linkedIndexAbles = invertedIndex.get(key);
			if (linkedIndexAbles != null) {
				for (T varIndexAble : linkedIndexAbles) {
					if (varIndexAble.equals(item)) {
						continue;
					}
				}
				linkedIndexAbles.add(item);
			} else {
				List<T> indexAbles = new ArrayList<T>();
				indexAbles.add(item);
				invertedIndex.put(key, indexAbles);
			}
		}
	}

	/**
	 * 删除待索引项
	 * 
	 * @param beanPreKey
	 *            可索引项的主键
	 */
	public synchronized void deleteInvertedItem(String beanPreKey) {
		T invertedIndexAble = invertedIndexItemsMap.get(beanPreKey);
		List<String> keys = getAllKeys(this
				.getIndexedAttrValue(invertedIndexAble));
		for (int i = 0; i < keys.size(); i++) {
			String key = keys.get(i);
			List<T> linkedIndexAbles = invertedIndex.get(key);
			if (linkedIndexAbles != null && linkedIndexAbles.size() > 0) {
				for (T varTItem : linkedIndexAbles) {
					if (this.getIndexedBeanPrekey(varTItem).equals(beanPreKey)) {
						linkedIndexAbles.remove(varTItem);
						break;
					}
				}
			}
			if (linkedIndexAbles.size() <= 0) {
				invertedIndex.remove(key);
			}
		}
	}

	/**
	 * 更新可索引项
	 * 
	 * @param bean
	 *            可索引项
	 */
	public synchronized void updateInvertedItem(T bean) {
		T oldItem = invertedIndexItemsMap.get(this.getIndexedBeanPrekey(bean));
		if (oldItem != null) {
			this.deleteInvertedItem(this.getIndexedBeanPrekey(oldItem));
			this.addInvertItem(bean);
		}
	}

	/**
	 * 构建索引
	 */
	private synchronized void buildInverteIndex() {
		for (T bean : invertedIndexItemsMap.values()) {
			this.addInvertItem(bean);
		}
	}

	/**
	 * 找出一个字符串所有的可能的倒排索引的键列表
	 * 
	 * @param str
	 *            字符串
	 * @return 一个字符串所有的可能的倒排索引的键列表
	 */
	private List<String> getAllKeys(String str) {
		List<String> result = new ArrayList<String>();
		char[] chars = str.toCharArray();
		for (int i = 0; i < chars.length; i++) {
			String key = "";
			for (int j = i; j < chars.length; j++) {
				key = key + chars[j];
				result.add(key);
			}
		}
		return result;
	}

	private String getIndexedBeanPrekey(T bean) {
		try {
			return this.prekeyMethod.invoke(bean).toString();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	private String getIndexedAttrValue(T bean) {
		try {
			return this.indexedAttrMethod.invoke(bean).toString();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	private Method buildAttrGetMethod(String attrName) {
		String firstLetter = attrName.substring(0, 1);
		firstLetter = firstLetter.toUpperCase();
		String methodName = "get" + firstLetter + attrName.substring(1);
		Method method = null;
		try {
			method = this.beanClass.getMethod(methodName);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
		return method;
	}
}