First send a sql command "set names utf8" specifying the character set, and then perform the insertion operation.

What is the character set of your database server? Execute the following command on the database server to check the character set first:

SHOW VARIABLES LIKE 'CHAR%'；

Finished, set the character set of the data submitted by the client to be the same as the character set of the database server...

Okay, it turns out that in the original jdbc operation, the string must be enclosed in single quotes

It is recommended that both the MySQL database server and client useUTF-8encoding. How to set the MySQL server encoding and client connection URL is similar to the following:

url="jdbc:mysql://localhost:3306/test?autoReconnect=true&useUnicode=true&characterEncoding=UTF-8"

Reference: JDBC url for MySQL configuration to use utf8 character encoding

String sql = "insert into shopping_car(name,book_name) values(?,?)";
stmt.setString(1, "123");
stmt.setString(2, book_name);

It is not recommended to use sql in this way, because sql injection is easy to occur. It is recommended to use another placeholder method, or ORM, such as mybatis, hibernate, etc.
Correction:

String sql = "insert into shopping_car(name,book_name) values(\"123\","+book_name+")"