background
When performing database operations of Java applications, you often encounter: connection holder is nullError. This error is usually caused by the connection object being empty or not being initialized correctly. This technical blog post will introduce the causes and solutions to this error in detail.
Cause of error
- The connection object is empty: Before performing database operations, you need to obtain a database connection. If the connection object is empty or is not initialized correctly, it will be thrown
: connection holder is nullError. - The connection object is not closed correctly: After using the database connection, you need to manually close the connection to free up the resource. If the connection is not closed in time, the next database operation will be thrown
: connection holder is nullError.
Solution
Here are some possible solutions for fixing: connection holder is nullError.
Method 1: Check whether the connection object is empty
First, you need to confirm that the database connection object is not empty. You can check the connection object by following the steps:
- Check out the method to get connections in the code, such as
(), make sure that the code obtained by the connection is correct. - Check whether the connection object is initialized correctly before performing the database operation. If it is not initialized, you can re-initialize the connection object.
Method 2: Close the connection object
If the connection object has been used, you need to manually close the connection to free up the resource. You can close the connection object by following the steps below:
- Confirm that all operations using the connection object have been executed.
- Calling the connection object
close()Method to close the connection.
Method 3: Use connection pool
Connection pooling is a mechanism for managing and reusing database connections that can provide better performance and resource management. Using a connection pool can avoid manually managing the opening and closing of connection objects and the error of empty connection objects. The steps to use the connection pool are as follows:
- Import connection pool libraries, such as C3P0, Tomcat JDBC, etc.
- Configure connection pool parameters, such as maximum number of connections, minimum number of connections, connection timeout, etc.
- Get the connection object through the connection pool, such as
()。 - After using the connection object, you do not need to manually close the connection, but return the connection object to the connection pool. Using connection pools can greatly simplify database connection management and improve application performance and reliability.
Summarize
: connection holder is nullErrors are usually caused by empty or not being initialized correctly. To resolve this error, we can check if the connection object is empty, manually close the connection object, or use a connection pool to manage the connection.
Scene
In a Java-based web application, we usually use a database to store and retrieve data. Here is a sample code showing how to handle SQLException when the connection object is empty.
javaCopy codeimport ;
import ;
import ;
import ;
import ;
public class DatabaseExample {
private Connection connection;
public void connectToDatabase() throws SQLException {
String url = "jdbc:mysql://localhost:3306/mydatabase";
String username = "root";
String password = "mypassword";
connection = (url, username, password);
}
public void executeQuery(String query) throws SQLException {
if (connection == null) {
throw new SQLException("Connection holder is null");
}
Statement statement = null;
ResultSet resultSet = null;
try {
statement = ();
resultSet = (query);
while (()) {
// Process the retrieved data
}
} finally {
if (resultSet != null) {
();
}
if (statement != null) {
();
}
}
}
public void closeConnection() throws SQLException {
if (connection != null) {
();
}
}
public static void main(String[] args) {
DatabaseExample example = new DatabaseExample();
try {
();
// Perform database operations...
("SELECT * FROM users");
();
} catch (SQLException e) {
();
}
}
}In the above example code, we first pass()Method to obtain the database connection. Then, we passexecuteQuery()The method executes an SQL query statement. Before executing the query, we check if the connection object is empty, and if it is empty, a SQLException is thrown. After executing the query, we passcloseConnection()Methods close the connection and release resources. When we run this sample code, if the connection object is empty, it will be thrown: connection holder is nullException.
()is a method to obtain database connections using data source connection pool in Java. In Java, using a connection pool to manage database connections is a common practice. Connection pooling provides applications with reusable and efficient database connections to reduce the overhead of establishing a connection to the database every time. The benefits of using data source connection pools include:
- Improve application performance: Connection pools can pre-create and manage a certain number of database connections that are reused when needed by the application, avoiding the overhead of frequent creation and destruction of connections. This can significantly improve the responsiveness and performance of your application.
- Control the number of connections to avoid resource exhaustion: Using a connection pool can limit the number of connections that are open simultaneously to avoid consuming too much database resources and avoiding database servers being congested by too many connections.
- Simplified connection management: The connection pool automatically manages the life cycle of the connection, including connection creation, allocation, return and closing operations. This simplifies application code and reduces connection management errors. Here is a sample code that demonstrates how to use a data source connection pool to obtain and use a database connection:
javaCopy codeimport ;
import ;
import ;
public class ConnectionPoolExample {
private DataSource dataSource;
public ConnectionPoolExample(DataSource dataSource) {
= dataSource;
}
public void performDatabaseOperation() {
Connection connection = null;
try {
connection = ();
// Use connection to perform database operations // ...
} catch (SQLException e) {
();
} finally {
if (connection != null) {
try {
();
} catch (SQLException e) {
();
}
}
}
}
public static void main(String[] args) {
// Create a data source DataSource dataSource = createDataSource();
// Create a connection pool example ConnectionPoolExample example = new ConnectionPoolExample(dataSource);
// Perform database operations ();
}
private static DataSource createDataSource() {
// Create and configure data sources // ...
return dataSource;
}
}In the example code above, we first create the data source and pass it as a parameter to the connection pool example. Then, inperformDatabaseOperation()In the method, we usegetConnection()Methods Get a database connection from the connection pool. After getting the connection, we can use that connection to perform some database operations. After completing the operation, we callclose()Method returns the connection to the connection pool. It should be noted that when using the connection pool to get the connection, we need to handle the SQLException exception in the code to prevent an exception from getting the connection. Also, after using the connection, make sure to manually close the connection to free up resources.
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