How does the Java Servlet initialization and destruction process work?

The Java Servlet initialization process includes loading bytecode, calling the init method to obtain configuration information and initializing the Servlet. The destruction process involves calling the destroy method to release resources, such as closing the database connection.

Java Servlet's initialization and destruction process

Initialization process

Servlet's The initialization process occurs when a Servlet is requested by a client for the first time and an instance is created. It involves the following steps:

1. The Java container loads the bytecode of the Servlet class.
2. Call the init method, which can accept the ServletConfig object as a parameter.
3. The Servlet class uses the ServletConfig object to obtain the configuration information provided by the container.
4. The Servlet class completes its initialization process, such as establishing a database connection or loading resources.

Practical case: Initialization of sample Servlet

public class MyServlet extends HttpServlet {

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);

        // 从 ServletConfig 获取配置信息
        String dbName = config.getInitParameter("dbName");
        String dbUser = config.getInitParameter("dbUser");
        String dbPassword = config.getInitParameter("dbPassword");

        // 使用配置信息初始化 Servlet
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/" + dbName, dbUser, dbPassword);
            this.conn = conn;
        } catch (ClassNotFoundException | SQLException e) {
            throw new ServletException("Error initializing database connection", e);
        }
    }
}

Destruction process

When the Servlet is no longer needed, The Java container will call its destroy method to perform the destruction process. This involves the following steps:

1. Call the destroy method, which will not accept any parameters.
2. The Servlet class releases resources, such as closing the database connection.

Practical case: Destruction of sample Servlet

public class MyServlet extends HttpServlet {

    private Connection conn;

    @Override
    public void destroy() {
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                // 处理关闭数据库连接的异常
            }
        }
        super.destroy();
    }
}

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