dynamically generate select sql like android does.

SQLUtils.java

/*
 * The MIT License (MIT)
 * Copyright (c) 2013 longkai(龙凯)
 */
package cn.newgxu.lab.core.util;

import java.util.Calendar;
import java.util.Date;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 通过方法调用来生成查询语句，这样比一味的使用封装要来得直接并且好用。
 * 可以直接将生成的查询语句返回给mybatis就好 
 * @author longkai
 * @email im.longkai@gmail.com
 * @since 13-7-30
 * @version 0.1.0.13-7-30
 */
public class SQLUtils {

	private static Pattern pattern = Pattern.compile("\\?");

	private static String columns(String[] columns) {
		if (columns == null || columns.length == 0) {
			return "*";
		}

		StringBuilder seletion = new StringBuilder();
		for (int i = 0; i < columns.length; i++) {
			seletion.append(columns[i]).append(",");
		}
		return seletion.substring(0, seletion.length() - 1);
	}

	private static String where(String where, Object[] args) {
		if (where == null || where.length() == 0) {
			return null;
		}
		if (args == null || args.length == 0) {
			return where;
		}

		StringBuffer _where = new StringBuffer();
		Matcher matcher = pattern.matcher(where);
		for (int i = 0; matcher.find(); i++) {
			matcher.appendReplacement(_where, injectArg(args[i]));
		}
		matcher.appendTail(_where);
		return _where.toString();
	}

	private static String injectArg(Object arg) {
		if (arg == null) {
			return "null";
		}

		if (arg instanceof Number) {
			return arg.toString();
		}

		StringBuilder value = new StringBuilder("'");
		if (arg instanceof Date) {
			Date d = (Date) arg;
			Calendar c = Calendar.getInstance();
			c.setTimeInMillis(d.getTime());
			value.append(c.get(Calendar.YEAR)).append("-")
					.append(c.get(Calendar.MONTH) + 1).append("-")
					.append(c.get(Calendar.DATE)).append(" ")
					.append(c.get(Calendar.HOUR)).append(":")
					.append(c.get(Calendar.MINUTE)).append(":")
					.append(c.get(Calendar.SECOND));
		} else {
			value.append(arg.toString());
		}
		return value.append("'").toString();
	}

	public static final String query(String table, String[] columns, String where, Object[] args, String groupBy, String having, String orderBy, String limit) {
		StringBuilder query = new StringBuilder();

		query.append("SELECT ").append(columns(columns)).append(" FROM ").append(table);

		where = where(where, args);
		if (where != null) {
			query.append(" WHERE ").append(where);
		}

		if (groupBy != null) {
			query.append(" GROUP BY ").append(groupBy);
		}

		if (having != null) {
			query.append(" HAVING ").append(having);
		}

		if (orderBy != null) {
			query.append(" ORDER BY ").append(orderBy);
		}

		if (limit != null) {
			query.append(" LIMIT ").append(limit);
		}
		return query.toString();
	}

}