Developing a stock trading platform with Java and Spring Boot involves building a backend server that handles stock data, user accounts, transactions, and integrating with stock market APIs. Here’s an overview of the steps involved:

1. Set up the Development Environment:
   Install Java Development Kit (JDK) and an Integrated Development Environment (IDE) like IntelliJ IDEA or Eclipse.
2. Create a Spring Boot Project:
   Use the Spring Initializr (https://start.spring.io/) to create a new Spring Boot project. Include necessary dependencies such as Spring Web, Spring Data JPA, Spring Security, and any additional dependencies you may need.
3. Design the Database Schema:
   Identify the entities required for your stock trading platform, such as stocks, user accounts, transactions, and portfolios. Design the database schema and define the relationships between entities.
4. Implement Entity Classes:
   Create Java classes representing the entities in your database schema. Annotate them with JPA annotations (@Entity, @Table, @Column, etc.) to define the mapping between the Java objects and database tables.
5. Implement Repository Interfaces:
   Create repository interfaces by extending the JpaRepository interface provided by Spring Data JPA. These interfaces will provide CRUD operations and querying capabilities for each entity.
6. Implement Service Classes:
   Create service classes to handle the business logic of your stock trading platform. These classes will interact with the repository interfaces to perform operations like stock data retrieval, user account management, and transaction processing.
7. Implement Controller Classes:
   Create RESTful API controller classes to handle incoming HTTP requests from the frontend application or other clients. Map these requests to appropriate service methods to perform operations like stock search, portfolio management, and transaction execution.
8. Integrate with Stock Market APIs:
   Utilize stock market APIs to fetch real-time stock data, historical data, and other relevant information. Integrate the API calls within your service classes to provide up-to-date stock information to users.
9. Implement User Authentication and Authorization:
   Implement user authentication and authorization features using Spring Security. Define authentication providers, configure security rules, and handle user registration, login, and role-based access control.
10. Implement Transaction Processing:
    Design and implement the logic for executing buy/sell transactions. Calculate available funds, validate stock availability, and update user account balances and stock holdings accordingly.
11. Implement Portfolio Management:
    Provide features for users to view their portfolios, including owned stocks, transaction history, and portfolio performance. Calculate portfolio values based on real-time stock prices.
12. Enhance User Experience:
    Implement features like real-time stock price updates, watchlists, trading alerts, and personalized recommendations to enhance the user experience of your stock trading platform.

Deployment:
Deploy your application to a Java application server or a cloud platform like AWS, Heroku, or Azure. Make sure to configure the necessary server settings and database connections for your backend server.

Building a stock trading platform with Java and Spring Boot requires careful consideration of security, real-time data integration, and scalability. Additionally, you may need to comply with regulatory requirements, implement risk management features, and integrate with payment gateways to facilitate transactions on your platform.