如何使用JDBC CallableStatement.wasNull()方法调用来查看最后一个OUT参数的值是否为 SQL NULL

此示例向您展示如何使用CallableStatement.wasNull()方法调用来查看最后一个OUT参数的值是否为 SQL NULL。

package org.kodejava.jdbc; import java.math.BigDecimal; 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/kodejava"; 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)) { // Prepares a call to the sored procedure String query = "call Get_Product_By_Price2(?, ?)"; CallableStatement cb = connection.prepareCall(query); // Sets the input parameter cb.setBigDecimal(1, new BigDecimal("50")); // Registers the OUT parameter cb.registerOutParameter(2, Types.VARCHAR); // Executes the query cb.executeQuery(); // Gets the OUT parameter value cb.getString(2); // Checks if the last OUT parameter has value of SQL NULL. // This method should be called only after calling a // getter method; otherwise, there is no value to use in // determining whether it is null or not. 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 Get_Product_By_Price2;; CREATE PROCEDURE Get_Product_By_Price2( IN product_price DECIMAL(10, 2), OUT product_name VARCHAR(50)) BEGIN SELECT NAME INTO product_name FROM products WHERE price = product_price; END;; DELIMITER ; 

Maven 依赖项

<!-- https://search.maven.org/remotecontent?filepath=mysql/mysql-connector-java/8.0.28/mysql-connector-java-8.0.28.jar --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.28</version> </dependency>