J2SE 讀取 Properties 設定檔的六種核心方法完整實作範例

統一載入入口：loadProperties 方法

以下程式碼展示一個完整的工具類別 JProperties，封裝了六種讀取 Properties 檔案的標準方式，並提供 ResourceBundleAdapter 適配器將 ResourceBundle 轉為 Properties 物件。

package com.kindani;

import java.util.*;
import java.io.*;

public class JProperties {
    public final static int BY_PROPERTIES = 1;
    public final static int BY_RESOURCEBUNDLE = 2;
    public final static int BY_PROPERTYRESOURCEBUNDLE = 3;
    public final static int BY_CLASS = 4;
    public final static int BY_CLASSLOADER = 5;
    public final static int BY_SYSTEM_CLASSLOADER = 6;

    public final static Properties loadProperties(final String name, final int type) throws IOException {
        Properties props = new Properties();
        InputStream in = null;
        try {
            switch (type) {
                case BY_PROPERTIES:
                    in = new BufferedInputStream(new FileInputStream(name));
                    props.load(in);
                    break;
                case BY_RESOURCEBUNDLE:
                    ResourceBundle rb = ResourceBundle.getBundle(name, Locale.getDefault());
                    props = new ResourceBundleAdapter(rb);
                    break;
                case BY_PROPERTYRESOURCEBUNDLE:
                    in = new BufferedInputStream(new FileInputStream(name));
                    rb = new PropertyResourceBundle(in);
                    props = new ResourceBundleAdapter(rb);
                    break;
                case BY_CLASS:
                    in = JProperties.class.getResourceAsStream(name);
                    props.load(in);
                    break;
                case BY_CLASSLOADER:
                    in = JProperties.class.getClassLoader().getResourceAsStream(name);
                    props.load(in);
                    break;
                case BY_SYSTEM_CLASSLOADER:
                    in = ClassLoader.getSystemResourceAsStream(name);
                    props.load(in);
                    break;
            }
        } finally {
            if (in != null) in.close();
        }
        return props;
    }

    // Servlet 環境下的替代方案（註解保留）
    /*
    public static Properties loadProperties(ServletContext context, String path) throws IOException {
        InputStream in = context.getResourceAsStream(path);
        Properties props = new Properties();
        props.load(in);
        in.close();
        return props;
    }
    */

    /** ResourceBundle 適配器：將 ResourceBundle 轉為 Properties */
    public static class ResourceBundleAdapter extends Properties {
        private final ResourceBundle bundle;

        public ResourceBundleAdapter(ResourceBundle rb) {
            if (!(rb instanceof PropertyResourceBundle)) {
                throw new IllegalArgumentException("僅支援 PropertyResourceBundle");
            }
            this.bundle = rb;
            Enumeration<String> keys = rb.getKeys();
            while (keys.hasMoreElements()) {
                String key = keys.nextElement();
                this.put(key, rb.getObject(key));
            }
        }

        // 代理常用方法
        public ResourceBundle getBundle(String baseName) { return ResourceBundle.getBundle(baseName); }
        public ResourceBundle getBundle(String baseName, Locale locale) { return ResourceBundle.getBundle(baseName, locale); }
        public ResourceBundle getBundle(String baseName, Locale locale, ClassLoader loader) { return ResourceBundle.getBundle(baseName, locale, loader); }
        public Enumeration<String> getKeys() { return bundle.getKeys(); }
        public Locale getLocale() { return bundle.getLocale(); }
        public Object getObject(String key) { return bundle.getObject(key); }
        public String getString(String key) { return bundle.getString(key); }
        public String[] getStringArray(String key) { return bundle.getStringArray(key); }
        protected Object handleGetObject(String key) { return ((PropertyResourceBundle) bundle).handleGetObject(key); }
    }
}

六種載入策略對照表

關鍵差異與選擇建議

• FileInputStream 系列：依賴檔案系統路徑，打包成 JAR 後失效，適合外部可編輯設定。
• Class/ClassLoader 系列：從 Classpath 載入，支援 JAR 內資源，適合隨應用程式部署的唯讀設定。
• ResourceBundle 系列：內建國際化支援（Locale）、快取機制，適合多語系資源；但鍵值皆為 String，且預設僅讀取 .properties 檔（無副檔名）。
• Servlet 環境：請使用 ServletContext.getResourceAsStream() 以支援 WAR 部署結構。

最佳實踐提醒

1. 統一使用 try-with-resources (Java 7+) 自動關閉流，避免洩漏。
2. 生產環境建議快取載入結果，避免重複 I/O。
3. 區分「部署時固定」與「執行期可變」設定，選擇對應載入策略。