一、JSON概念 JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。
JSON数据格式示例： { "学生": [ {"姓名":"小明","年龄":23}, {"姓名":"大憨","年龄":24} ] }
一个对象以“{”（左括号）开始，“}”（右括号）结束 一个数组以“[”（左中括号）开始，“]”（右中括号）结束
二、JSON与XML XML数据格式： <?xml version="1.0" encoding="utf-8"?> <country> <province> <name>黑龙江</name> <cities> <city>哈尔滨</city> <city>大庆</city> </cities> </province> <province> <name>广东</name> <cities> <city>广州</city> <city>深圳</city> <city>珠海</city> </cities> </province> </country>
编码的可读性，xml有明显的优势，毕竟人类的语言更贴近这样的说明结构。json读起来更像一个数据块，读起来就比较费解了。不过，我们读起来费解的语言，恰恰是适合机器阅读。 JSON难阅读，试试：JSON在线编辑器 JSON没有多余的标签，所以JSON比xml网络传输效率更高。
三、JSON与ABAP格式互转 1、cl_trex_json_serializer、cl_trex_json_deserializer方式 DATA: lo_json_ser TYPE REF TO cl_trex_json_serializer, lo_json_des TYPE REF TO cl_trex_json_deserializer. DATA: json_string TYPE string.
DATA:BEGIN OF lt_spfli OCCURS 0, carrid TYPE spfli-carrid, connid TYPE spfli-connid, cityfrom TYPE spfli-cityfrom, countryto TYPE spfli-countryto, END OF lt_spfli.
START-OF-SELECTION.
SELECT carrid connid cityfrom countryto UP TO 10 ROWS INTO TABLE lt_spfli FROM spfli.
*内表->JSON CREATE OBJECT lo_json_ser EXPORTING data = lt_spfli[]. CALL METHOD lo_json_ser->serialize. CALL METHOD lo_json_ser->get_data RECEIVING rval = json_string.
WRITE:json_string. CLEAR:lt_spfli[]. *JSON->内表 CREATE OBJECT lo_json_des. CALL METHOD lo_json_des->deserialize EXPORTING json = json_string IMPORTING abap = lt_spfli[].
该种转换方式，生成的JSON，KEY关键字没有引号，字符串中包含空格，如果与第三方系统做接口时，就会因为JSON格式问题，导致接口失败。
2、CALL TRANSFORMATION id 方式 DATA:BEGIN OF lt_spfli OCCURS 0, carrid TYPE spfli-carrid, connid TYPE spfli-connid, cityfrom TYPE spfli-cityfrom, countryto TYPE spfli-countryto, END OF lt_spfli. DATA: lo_writer TYPE REF TO cl_sxml_string_writer, lv_output_length TYPE i, lt_binary_tab TYPE STANDARD TABLE OF sdokcntbin, lv_jsonx TYPE xstring, lv_json TYPE string.
SELECT carrid connid cityfrom countryto UP TO 10 ROWS INTO TABLE lt_spfli FROM spfli.
* ABAP to JSON lo_writer = cl_sxml_string_writer=>create( type = if_sxml=>co_xt_json ). CALL TRANSFORMATION id SOURCE text = lt_spfli[] RESULT XML lo_writer. lv_jsonx = lo_writer->get_output( ).
CALL FUNCTION 'SCMS_XSTRING_TO_BINARY' EXPORTING buffer = lv_jsonx IMPORTING output_length = lv_output_length TABLES binary_tab = lt_binary_tab.
CALL FUNCTION 'SCMS_BINARY_TO_STRING' EXPORTING input_length = lv_output_length IMPORTING text_buffer = lv_json output_length = lv_output_length TABLES binary_tab = lt_binary_tab.
* JSON to ABAP CALL TRANSFORMATION id SOURCE XML lv_jsonx RESULT text = lt_spfli.
该种JSON转换生成的数据，比内表数据多了一部分“TEXT”字符串，也不是很满意
3、/UI2/CL_JSON方式 DATA: lt_flight TYPE STANDARD TABLE OF sflight, lrf_descr TYPE REF TO cl_abap_typedescr, lv_json TYPE string.
SELECT * FROM sflight INTO TABLE lt_flight.
* serialize table lt_flight into JSON, skipping initial fields and converting ABAP field names into camelCase lv_json = /ui2/cl_json=>serialize( data = lt_flight compress = abap_true pretty_name = /ui2/cl_json=>pretty_mode-camel_case ). WRITE / lv_json.
CLEAR lt_flight.
* deserialize JSON string json into internal table lt_flight doing camelCase to ABAP like field name mapping /ui2/cl_json=>deserialize( EXPORTING json = lv_json pretty_name = /ui2/cl_json=>pretty_mode-camel_case CHANGING data = lt_flight ).
* serialize ABAP object into JSON string lrf_descr = cl_abap_typedescr=>describe_by_data( lt_flight ). lv_json = /ui2/cl_json=>serialize( lrf_descr ). WRITE / lv_json.
/UI2/CL_JSON方式转换生成的JSON格式就完美了，他不仅支持结构、内表转换成JSON，还支持嵌套结构deep structure这种复杂的结构，了解更多请参考： https://wiki.scn.sap.com/wiki/display/Snippets/One more ABAP to JSON Serializer and Deserializer
注意：ABAP中定义变量是不区分大小写，而JAVA中变量是区分大小写的，所以需要对字符串替换一下，如下： REPLACE ALL OCCURRENCES OF 'contactname' IN post_string WITH 'contactName'.
