queryhelp.java

Java案例开发集锦,里面提供了很好的学习例子

package simpleforum.database;

/**
 * @author wangmj
 */
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.Hashtable;
import java.util.Vector;

public class QueryHelp {
	/**
	 * 传入一个查询sql语句然后将结果放入Vector中。
	 * 字段名全部为大写，所以像下面这样才能取道正确的值： hash.get("FIELD");
	 * @param querySql
	 * @return
	 */
	public static Vector getHelp(String querySql) {
		Connection connection = null;
		PreparedStatement statement = null;
		ResultSet resultset = null;
		Vector vector =	new Vector();
		//这里不能使用空句柄。
		//教训，最好不要使用null，除非你能够通过下面的语句取得一个对象。
		//String对象也是如此。
		try {
			connection = DataBaseConn.getConnection();
			connection.setReadOnly(true);
			statement = connection.prepareStatement(querySql);
			resultset = statement.executeQuery();
			ResultSetMetaData resultsetmetadata = resultset.getMetaData();
			int i = resultsetmetadata.getColumnCount();
			String as[] = new String[i];
			for (int j = 1; j <= i; j++)
				as[j - 1] = (resultsetmetadata.getColumnName(j)).toUpperCase();
			//所有的key值均为字段的大写
			Hashtable hashtable;
			for (; resultset.next(); vector.addElement(hashtable)) {
				hashtable = new Hashtable();
				for (int k = 1; k <= i; k++) {
					Object obj = resultset.getObject(k);
					String s = as[k - 1];
					if (obj != null)
						hashtable.put(s, obj);
					else
						hashtable.put(s, "");
				}

			}

		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			try {
				if (resultset != null)
					resultset.close();
			} catch (SQLException e) {
			}
			try {
				if (statement != null)
					statement.close();
			} catch (SQLException e) {
			}
			try {
				if (connection != null)
					connection.close();
			} catch (SQLException e) {
			}
		}
		return vector;
	}
	/**
	 * 本方法的使用应该注意，只能使用统计函数count(*)例如： 
	 * select count(*) from forumpost where forumid=1; 
	 * @param querySql
	 * @return
	 */
	public static int getInt(String querySql) {
		int temp = 0;
		Connection conn = DataBaseConn.getConnection();
		PreparedStatement statement = null;
		ResultSet rst = null;
		try{
			statement = conn.prepareStatement(querySql);
			rst = statement.executeQuery();
			while(rst.next()){
				temp = rst.getInt(1);
			}
		}catch(SQLException e){
			System.out.println("出现异常：\n"+"QueryHelp.getInt("+querySql+")\n");
			System.out.println("下面是详细信息：\n");
			e.printStackTrace();
		}finally{
			try {
				if (rst != null)
					rst.close();
			} catch (SQLException e) {
			}
			try {
				if (statement != null)
					statement.close();
			} catch (SQLException e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (SQLException e) {
			}
		}
		return temp;
	}	
}