List字符串

		List<String> list = Arrays.asList("张三", "李四", "王五");
        String collect = String.join("，", list);
        //也可以用 stream ，但是不推荐
//        list.stream().collect(Collectors.joining("，"));
        System.out.println(collect);

List对象

获取对象集合里的字符串进行拼接（传统写法）

		List<User> list = new ArrayList<>();
        for (long i = 0; i < 3; i++) {
            User user = new User();
            user.setUsername("张" + i);
            list.add(user);
        }
        StringBuilder addSplitString = new StringBuilder();
        boolean isFirst = true;
        for (User user : list) {
            if (!isFirst) {
                addSplitString.append("，");
            }
            addSplitString.append(user.getUsername());
            isFirst = false;
        }
        System.out.println(addSplitString);

JDK1.8 stream 获取对象集合里的字符串进行拼接

		List<User> list = new ArrayList<>();
        for (long i = 0; i < 3; i++) {
            User user = new User();
            user.setUsername("张" + i);
            list.add(user);
        }
        String collect = list.stream().map(User::getUsername).collect(Collectors.joining("，"));
        System.out.println(collect);