小小的总结下

tableName代表数据库中的表
fieldName代表需要查询的数据库表中的列名
cond代表查询的条件表达式，
cond.getCondition()得到具体的表达式

查询函数

public static List<Map<String, Object>> query(Connection con,
			String tableName, String[] fieldName, Condition cond){
		
		List<Map<String, Object>> result = new ArrayList<Map<String, Object>>();
		
		PreparedStatement psmt = null;
		ResultSet rs = null;
		
		try{
			StringBuffer sql = new StringBuffer("select ");
			StringBuffer tobeQueryed = new StringBuffer();
			
			if(fieldName.length!= 0){
				for(String field : fieldName){
					tobeQueryed.append(field + " ,");
				}
				tobeQueryed = new StringBuffer(tobeQueryed.substring(0, tobeQueryed.length()-1));
				
			}else{
				tobeQueryed.append(" * ");
			}
			
			sql.append(tobeQueryed);
			sql.append(" from "+tableName+ " where ");
			
			if (cond != null)
				sql.append(cond.getCondition());
	
			
			System.out.println("sql:"+sql);
			psmt = con.prepareStatement(sql.toString());
						
			//按照查询字段的数值设定，需要对应数据库中的类型！很重要的！
			if( cond!=null ){
				System.out.println(cond.getQueryValues());
				Vector<Object> values = cond.getQueryValues();
				int i = 1;
				for(Object value : values){
					if (value != null) {
						psmt.setObject(i, value);
						i++;
					}
				}
			}
			rs = psmt.executeQuery();
			
			while (rs.next()) {
				Map<String, Object> curResult = new HashMap<String, Object>();
				for (int j = 0; j < fieldName.length; j++) {
					Object object = rs.getObject(j + 1);
					if ( object instanceof String  && object !=null ){
						curResult.put(fieldName[j], ((String)object).trim());
					}
					else{
						curResult.put(fieldName[j], object);
					}
				}
				result.add(curResult);
			}
		}catch(Exception e){
			
		}
		return result;
	}
}

Condition类，构造条件表达式
Expression类代表任意的一个表达式

public class Condition {

	private Vector<Expression> expressions = new Vector<Expression>();
	private Vector<LogicOperator> operators = new Vector<LogicOperator>();
	
	public void addExpression(Expression exp){
		if(expressions.size()>0){
			System.out.println("and");
			operators.add(LogicOperator.and);
		}
		expressions.add(exp);
	}
	//得到查询字段对应的值
	public Vector<Object> getQueryValues(){
		Vector<Object> values = new Vector<Object>();
		
		for(int i=0; i<expressions.size(); i++){
			values.add(expressions.get(i).rightExp);
		}
		
		return values;
	}

	public String getCondition(){
		String sql = "";
		int  i;
		for(i=0; i<operators.size(); i++){
			sql = sql + expressions.get(i).getSQL() + " "+Expression.LogicOperatorToString(operators.get(i))+ " ";
		}
		sql = sql + expressions.get(i).getSQL();
		
		return sql;
	}
}