（在做了大量的研究之后，答案是：）
从下载必要的库http://mvnrepository.com/ 寄存器命令所需。
Pig的脚本如下：

register 'libs/elephant-bird-core-4.1.jar';
register 'libs/elephant-bird-pig-4.1.jar';
register 'libs/guava-14.0.1.jar';
register 'libs/json-simple-1.1.1.jar';
register 'libs/piggybank.jar';

define decode_json com.twitter.elephantbird.pig.piggybank.JsonStringToMap();

e1 = load '$filename' using PigStorage() as (
    date: chararray,
    event_name: chararray,
    event_details_str: chararray,
);

-- Remove the header row:
e2 = filter e1 by not date matches '.*DATE';

-- Convert the event_details from a JSON string to a map:
events = foreach e2 generate *, decode_json(event_details_str) as event_details;

mbells的答案很好，我一直在努力的一件事是如何检索Map值。下面是从事件Map检索key1、key2的示例。

fields = FOREACH events GENERATE events#'key1', events#'key2';