Java 为什么CallableStatement在我的代码中返回空值？

首先，我创建一个过程

package procedure;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class Pro2 {
enter code herestatic String className = "com.mysql.jdbc.Driver";
static String url = "jdbc:mysql://localhost:3306/testdb";
static String user = "root";
static String password = "";
public static void main(String[] args) {
    Connection con;
    Statement stmt;
    try {
        String drop2 = "DROP PROCEDURE IF EXISTS au2;";
        String query2 = ""
                + "CREATE PROCEDURE au2(\n"
                + "    INOUT id VARCHAR(11),\n"
                + "    OUT fname VARCHAR(20),\n"
                + "    OUT lname VARCHAR(40),\n"
                + "    OUT phone VARCHAR(12),\n"
                + "    OUT address VARCHAR(100),\n"
                + "    OUT city VARCHAR(20),\n"
                + "    OUT state VARCHAR(20),\n"
                + "    OUT zip VARCHAR(5)\n"
                + ")\n"
                + "BEGIN\n"
                + "    SELECT * FROM author WHERE au_id = id ; \n"
                + "END";

            Class.forName(className);
            con = DriverManager.getConnection(url, user, password);
            stmt = con.createStatement();            
            stmt.executeUpdate(drop2);
            stmt.executeUpdate(query2);

            stmt.close();
            con.close();
            } catch (ClassNotFoundException | SQLException e) {
            System.err.println("Error: "+e.getMessage());
            }
    }
}

然后我调用它，但我得到了除id之外的所有空值

package procedure;

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Types;
public class CallPro2 {

static String className = "com.mysql.jdbc.Driver";
static String url = "jdbc:mysql://localhost:3306/testdb";
static String user = "root";
static String password = "";

public static void main(String[] args) {
    Connection con;
    String query2 = "{call au2(?,?,?,?,?,?,?,?)}";
    try {
        Class.forName(className);
        con = DriverManager.getConnection(url, user, password);

        CallableStatement cstmt = con.prepareCall(query2);
        cstmt.setString(1, "A00001");
        cstmt.registerOutParameter(2, Types.VARCHAR);
        cstmt.registerOutParameter(3, Types.VARCHAR);
        cstmt.registerOutParameter(4, Types.VARCHAR);
        cstmt.registerOutParameter(5, Types.VARCHAR);
        cstmt.registerOutParameter(6, Types.VARCHAR);
        cstmt.registerOutParameter(7, Types.VARCHAR);
        cstmt.registerOutParameter(8, Types.VARCHAR);
        cstmt.execute();

        System.out.println(""
                + "Author ID: "+cstmt.getString(1)+"\n"
                + "First name: " + cstmt.getString(2) + "\n"
                + "Last name: " + cstmt.getString(3) + "\n"
                + "Phone: " + cstmt.getString(4) + "\n"
                + "Address: " + cstmt.getString(5) + "\n"
                + "City: " + cstmt.getString(6) + "\n"
                + "State: " + cstmt.getString(7) + "\n"
                + "Zipcode: " + cstmt.getString(8));                        
            con.close();
        } catch (SQLException | ClassNotFoundException e) {
             System.err.println("Error: " + e.getMessage());
        }
    }
}

当我像那样运行程序时，结果是：

Author ID: A00001
First name: null
Last name: null
Phone: null
Address: null
City: null
State: null
Zipcode: null
BUILD SUCCESSFUL (total time: 1 second)

---

您从未在存储过程中设置参数。PS：您可以删除它们并直接（从存储过程）获得查询结果。