private String getSql(String[] param, String [] signs){
        // 符号为空要默认为"="？
		if (signs == null) {
			signs = new String[param.length];
			for (int i = 0; i < param.length; i++) {
				signs[i] = "=";
			}
		}
    	StringBuilder sb = new StringBuilder();
    	sb.append("from ").append(type.getSimpleName()).append(" a where ");
    	for(int i=0;i<param.length ;i++){
    		sb.append(" a.").append(param[i]).append(signs[i]).append(":").append(param[i]);
    		if(i+1 != param.length){
    			sb.append(" and ");
    		}
    	}
    	return sb.toString();
    }