jdbc怎么查询表中所有数据

```java

import java.sql.*;

public class Main {

public static void main(String[] args) {

String url = "jdbc:mysql://localhost:3306/database_name";

String username = "username";

String password = "password";

try {

Connection conn = DriverManager.getConnection(url, username, password);

Statement stmt = conn.createStatement();

String query = "SELECT * FROM table_name";

ResultSet rs = stmt.executeQuery(query);

while (rs.next()) {

// 获取每一行数据的值

int id = rs.getInt("id");

String name = rs.getString("name");

int age = rs.getInt("age");

System.out.println("ID: " + id + ", Name: " + name + ", Age: " + age);

}

conn.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

}

```

在上面的代码中，将数据库连接信息和查询语句替换为你自己的数据库信息和表名，然后运行代码，就可以查询表中的所有数据。