記錄器服務

以下示例顯示如何通過 ServiceLoader 例項化一個類以進行日誌記錄。

服務

package servicetest;

import java.io.IOException;

public interface Logger extends AutoCloseable {
    
    void log(String message) throws IOException;
}

服務的實現

以下實現只是將訊息寫入 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() {
    }

}

以下實現將訊息寫入文字檔案：

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 /服務/ servicetest.Logger

META-INF/services/servicetest.Logger 檔案列出了 Logger 實現的名稱。

servicetest.logger.ConsoleLogger
servicetest.logger.FileLogger

用法

以下 main 方法將訊息寫入所有可用的記錄器。記錄器使用 ServiceLoader 例項化。

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);
        }
    }
}