Java Resource Management

Java Resources#

Memory resources: Memory space occupied by objects, arrays, etc.
Physical resources: File handles, database connections, network connections, etc.
Differences between memory and physical resources

Memory resources are automatically managed by JVM, while physical resources need to be manually managed.
When an object is no longer referenced, memory resources are automatically reclaimed, while physical resources remain occupied.
Example: Memory resources: Reading a book in the reading area and leaving after finishing; Physical resources: Borrowing a book requires returning it actively; if not returned, it will continue to occupy the book.

Basic Principles of Java Memory Management#

Heap memory: Stores object instances.
Stack memory: Stores primitive data types and object references.

How try-with-resources Works in Java Physical Resource Management#

This is a feature introduced in Java 7.
Any class that implements the AutoCloseable interface can be used.
The compiler automatically converts it into code with finally.

// When we write code like this:
try (FileInputStream file = new FileInputStream("test.txt")) {
    // Use the file
}

// The compiler automatically converts it to code like this:
FileInputStream file = new FileInputStream("test.txt");
try {
    // Use the file
} finally {
    if (file != null) {
        file.close();
    }
}

Methods for Managing Physical Resources in Java#

Traditional method (not recommended)

FileInputStream file = null;
try {
    file = new FileInputStream("test.txt");
    // Use the file
} catch (Exception e) {
    // Handle exception
} finally {
    if (file != null) {
        file.close(); // Manually close the resource
    }
}

Modern method (recommended)

try (FileInputStream file = new FileInputStream("test.txt")) {
    // Use the file
} catch (Exception e) {
    // Handle exception
} // Automatically close the resource

Complete summary of Java resource management:

Core principles:
Use try-with-resources to automatically manage resources.
Correctly handle checked exceptions.
Follow the "last in, first out" order for resource closure.

Resource types:
Common resources that need management:

InputStream/OutputStream (file operations)
Connection/Statement/ResultSet (database operations)
Socket (network connections)
Channel (NIO operations)

Standard template:

try (Resource1 r1 = new Resource1();    
     Resource2 r2 = new Resource2()) {
    // Use the resources
} catch (Exception e) {
    // Exception handling
}

Ways to Manage Java Resources:#

File system resources:

Using the File class
File file = new File("test.txt");
Using the Path interface (Java 7+)
Path path = Paths.get("test.txt");

Network resources:

Using the URL class
URL url = new URL("https://example.com");
URLConnection conn = url.openConnection();
Using Socket
Socket socket = new Socket("localhost", 8080);

Classpath resources:

Using ClassLoader
InputStream is = getClass().getClassLoader().getResourceAsStream("config.properties");
Using Class
InputStream is = MyClass.class.getResourceAsStream("/config.properties");

Database resources:

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