java8 ->StringJoiner + String.join

/**
     * StringJoiner
     * @Author: Mr.li
     * @Date: 2020/9/8
     */
    @Test
    public void demo4() {

        List<String> names = new ArrayList<String>();
        names.add("1");
        names.add("2");
        names.add("3");
        System.out.println(String.join("-", names));

        String[] arrStr = new String[]{"a", "b", "c"};
        System.out.println(String.join("-", arrStr));


        List<User> cr = new ArrayList<>();
        User crd = new User();
        crd.setContactRoleName("LEGAL");
        User crd1 = new User();
        crd1.setContactRoleName("MAIN");
        cr.add(crd);
        cr.add(crd1);

        StringJoiner roleJoiner = new StringJoiner(",");//需要的间隔符
        // Lambda 实现拼接
        cr.forEach(role -> roleJoiner.add(role.getContactRoleName()));

        System.out.println("Lambda实现拼接结果：" + roleJoiner.toString());

        StringJoiner roleJoiner1 = new StringJoiner(",");//需要的间隔符
        for (User role : cr) {
            roleJoiner1.add(role.getContactRoleName());
        }

        System.out.println("使用for循环时间拼接结果：" + roleJoiner1);
    }

result: