JDBC之ParameterMetaData

1、ParameterMetaData pmd = preparedStatement.getParameterMetaData();

2、通过 ParameterMetaData可以获得参数信息。

JdbcUtils中的代码：

package cn.itcast.jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;/** * Jdbc工具类 */public final class JdbcUtils {//省略localhost:3306private static String url = "jdbc:mysql:///jdbc";private static String url2 = "jdbc:mysql:///jdbc?user=root&password=root&"+ "useUnicode=true&generateSimpleParameterMetadata=true";private static String username = "root";private static String password = "root";/** * 构造器私用,防止直接创建对象, * 当然通过反射可以创建 */private JdbcUtils(){}//保证只是注册一次驱动static{try {Class.forName("com.mysql.jdbc.Driver");} catch (ClassNotFoundException e) {throw new ExceptionInInitializerError(e);}}/** * 获取连接 * @return * @throws SQLException */public static Connection getConnection() throws SQLException {return DriverManager.getConnection(url2);//return DriverManager.getConnection(url, username, password);}/** * 释放资源 */public static void free(ResultSet rs, Statement st, Connection conn) {//规范的关系连接的方式try{if(rs != null) {rs.close();}} catch (SQLException e) {e.printStackTrace();}finally{try{if(st != null) {st.close();}} catch (SQLException e) {e.printStackTrace();}finally {if(conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}}}}

测试类中的代码：

package cn.itcast.jdbc;import java.sql.Connection;import java.sql.ParameterMetaData;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import org.junit.Test;/** * 参数的原信息测试 */public class ParameterMetaTest {/** * 测试从数据库中读取数据 * @throws SQLException */@Testpublic void testRead() throws SQLException {//第二个参数传java.sql.Date或java.util.Date都可以测试成功Object[] params = new Object[] { "lisi",new java.util.Date(System.currentTimeMillis()), 100f };read("select * from user where name = ? and birthday < ? and money > ?", params);}/** * 从数据库中读取数据 * @param sql * @param params * @throws SQLException */static void read(String sql, Object[] params) throws SQLException {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JdbcUtils.getConnection();ps = conn.prepareStatement(sql);//获取参数原信息ParameterMetaData pmd = ps.getParameterMetaData();//通过获取参数个数来提高代码灵活性int count = pmd.getParameterCount();System.out.println("参数个数:" + count);//打印数据库参数信息,MySQL的输出并不准确for(int i = 1; i <= count; i ++) {System.out.print(pmd.getParameterClassName(i) + "\t");System.out.print(pmd.getParameterType(i) + "\t");System.out.println(pmd.getParameterTypeName(i));ps.setObject(i, params[i - 1]);}//执行查询操作rs = ps.executeQuery();while(rs.next()) {System.out.println(rs.getInt("id") + "\t"+ rs.getString("name") + "\t" + rs.getDate("birthday") + "\t" + rs.getFloat("money"));}} finally {JdbcUtils.free(rs, ps, conn);}}}

测试结果：

参数个数:3
java.lang.String 12VARCHAR
java.lang.String 12VARCHAR
java.lang.String 12VARCHAR
2 lisi 2017-06-06 310.0