记录器服务
以下示例显示如何通过 ServiceLoader
实例化一个类以进行日志记录。
服务
package servicetest;
import java.io.IOException;
public interface Logger extends AutoCloseable {
void log(String message) throws IOException;
}
服务的实现
以下实现只是将消息写入 System.err
package servicetest.logger;
import servicetest.Logger;
public class ConsoleLogger implements Logger {
@Override
public void log(String message) {
System.err.println(message);
}
@Override
public void close() {
}
}
以下实现将消息写入文本文件:
package servicetest.logger;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import servicetest.Logger;
public class FileLogger implements Logger {
private final BufferedWriter writer;
public FileLogger() throws IOException {
writer = new BufferedWriter(new FileWriter("log.txt"));
}
@Override
public void log(String message) throws IOException {
writer.append(message);
writer.newLine();
}
@Override
public void close() throws IOException {
writer.close();
}
}
META-INF /服务/ servicetest.Logger
META-INF/services/servicetest.Logger
文件列出了 Logger
实现的名称。
servicetest.logger.ConsoleLogger
servicetest.logger.FileLogger
用法
以下 main
方法将消息写入所有可用的记录器。记录器使用 ServiceLoader
实例化。
public static void main(String[] args) throws Exception {
final String message = "Hello World!";
// get ServiceLoader for Logger
ServiceLoader<Logger> loader = ServiceLoader.load(servicetest.Logger.class);
// iterate through instances of available loggers, writing the message to each one
Iterator<Logger> iterator = loader.iterator();
while (iterator.hasNext()) {
try (Logger logger = iterator.next()) {
logger.log(message);
}
}
}