java properties增删改查     public static void main(String args[]) throws IOException {    Properties prop = new Properties();    OutputStream out = new FileOutputStream("D:\\workspace\\JavaStudy\\src\\test\\test.properties");        /**     * 新增逻辑：     * 1.必须先读取文件原有内容     * 2.增加新的记录以后，再一起保存     */    //1.先读取文件原有内容    Map toSaveMap = new HashMap();    Set keys = prop.keySet();    for(Iterator itr = keys.iterator(); itr.hasNext();){     String key = (String) itr.next();     Object value = prop.get(key);     toSaveMap.put(key, value);    }    //2.增加你需要增加的属性内容    toSaveMap.put("name", "zhang san");    toSaveMap.put("age", "25");    prop.putAll(toSaveMap);    prop.store(out, "==== after add ====");        /**     * 修改逻辑：重新设置对应Key的值即可，非常简单     */    prop.clear();    toSaveMap.put("name", "li si");    toSaveMap.put("age", "26");    prop.putAll(toSaveMap);    prop.store(out, "==== after modify ====");        /**     * 删除逻辑：找到对应的key，删除即可     */      prop.clear();    toSaveMap.remove("name");    prop.putAll(toSaveMap);    prop.store(out, "==== after remove ===="));        /**     * 查询逻辑：     */    InputStream in = new FileInputStream("D:\\workspace\\JavaStudy\\src\\test\\test.properties");    prop.load(in);    System.out.println("name: " + prop.get("name"));    System.out.println("age: " + prop.get("age"));       }