Java如何检查OUT参数值是否为null？
本示例向您展示如何使用CallableStatement.wasNull()方法调用来查看最后一个OUT参数是否具有SQL值NULL。
package org.nhooo.example.jdbc;
import java.sql.Connection;
import java.sql.CallableStatement;
import java.sql.DriverManager;
import java.sql.Types;
import java.sql.SQLException;
public class WasNullExample {
private static final String URL = "jdbc:mysql://localhost/nhooo";
private static final String USERNAME = "root";
private static final String PASSWORD = "";
public static void main(String[] args) {
try (Connection connection =
DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
//准备调用sored过程
String query = "call GetProductByPrice2(?, ?)";
CallableStatement cb = connection.prepareCall(query);
//设置输入参数
cb.setDouble(1, 40d);
//注册OUT参数
cb.registerOutParameter(2, Types.VARCHAR);
//执行查询
cb.executeQuery();
//获取OUT参数值
cb.getString(2);
//检查最后一个OUT参数的值是否为SQLNULL。
//仅在调用a之后，才应调用此方法
//吸气方法否则，没有价值可用于
//确定它是否为空。
if (cb.wasNull()) {
System.out.println("Product has an SQL NULL value");
} else {
System.out.println("Product: " + cb.getString(2));
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}这是我们在上面的示例中调用的存储过程脚本。
DELIMITER ;;
DROP PROCEDURE IF EXISTS GetProductByPrice2;;
CREATE PROCEDURE GetProductByPrice2(IN product_price DECIMAL, OUT product_name VARCHAR(50))
BEGIN
SELECT NAME INTO product_name FROM products WHERE price = product_price;
END;;
DELIMITER ;Maven依赖
<!-- https://search.maven.org/remotecontent?filepath=mysql/mysql-connector-java/8.0.17/mysql-connector-java-8.0.17.jar -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.17</version>
</dependency>