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The Java example does not implement the Chain of Responsibility pattern since it involves messages handled by multiple loggers. Tags: Reverted section blanking |
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{{wikibooks|Computer Science Design Patterns|Chain of responsibility|Chain-of-responsibility implementations in various languages}}
=== Java example ===
Below is an example of this pattern in Java.
A logger is created using a chain of loggers, each one configured with different log levels.
<syntaxhighlight lang="java" line="1">
import java.util.Arrays;
import java.util.EnumSet;
import java.util.function.Consumer;
@FunctionalInterface
public interface Logger {
public enum LogLevel {
INFO, DEBUG, WARNING, ERROR, FUNCTIONAL_MESSAGE, FUNCTIONAL_ERROR;
public static LogLevel[] all() {
return values();
}
}
abstract void message(String msg, LogLevel severity);
default Logger appendNext(Logger nextLogger) {
return (msg, severity) -> {
message(msg, severity);
nextLogger.message(msg, severity);
};
}
static Logger writeLogger(LogLevel[] levels, Consumer<String> stringConsumer) {
EnumSet<LogLevel> set = EnumSet.copyOf(Arrays.asList(levels));
return (msg, severity) -> {
if (set.contains(severity)) {
stringConsumer.accept(msg);
}
};
}
static Logger consoleLogger(LogLevel... levels) {
return writeLogger(levels, msg -> System.err.println("Writing to console: " + msg));
}
static Logger emailLogger(LogLevel... levels) {
return writeLogger(levels, msg -> System.err.println("Sending via email: " + msg));
}
static Logger fileLogger(LogLevel... levels) {
return writeLogger(levels, msg -> System.err.println("Writing to Log File: " + msg));
}
}
class Runner {
public static void main(String[] args) {
// Build an immutable chain of responsibility
Logger logger = consoleLogger(LogLevel.all())
.appendNext(emailLogger(LogLevel.FUNCTIONAL_MESSAGE, LogLevel.FUNCTIONAL_ERROR))
.appendNext(fileLogger(LogLevel.WARNING, LogLevel.ERROR));
// Handled by consoleLogger since the console has a LogLevel of all
logger.message("Entering function ProcessOrder().", LogLevel.DEBUG);
logger.message("Order record retrieved.", LogLevel.INFO);
// Handled by consoleLogger and emailLogger since emailLogger implements Functional_Error & Functional_Message
logger.message("Unable to Process Order ORD1 Dated D1 For Customer C1.", LogLevel.FUNCTIONAL_ERROR);
logger.message("Order Dispatched.", LogLevel.FUNCTIONAL_MESSAGE);
// Handled by consoleLogger and fileLogger since fileLogger implements Warning & Error
logger.message("Customer Address details missing in Branch DataBase.", LogLevel.WARNING);
logger.message("Customer Address details missing in Organization DataBase.", LogLevel.ERROR);
}
}
</syntaxhighlight>
=== C# example ===
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