博客 · 2023年9月13日 · Steve Simpson · 集成

JSON 狂欢节：Apex 外部调用中固定反序列化与动态反序列化的对决

引言：

你好！我是 Steve Simpson，Salesforce 认证技术架构师和讲师。在这篇博客中，我们将探讨在 Salesforce 中进行 Apex 外部调用时解析 JSON 的不同技术。我们会讨论固定结构的 JSON 解析、动态 JSON 解析，以及一种兼具灵活性和易用性的混合方式。

第 1 部分：用单行反序列化进行固定结构的 JSON 解析

当你面对的是不常变化的简单 JSON 结构时，你可以创建一个与 JSON 结构完全对应的 Apex 类。这种做法让你只用一行代码就能把 JSON 字符串反序列化成一个数组。对于静态的 JSON 结构，这种方法强大而高效。

截图：OpenSky 航班到达 API 的文档，列出了它的请求参数 Postman 截图：对 OpenSky 到达 API 的一次 GET 调用，以 JSON 格式返回航班数据

public class OS_FlightStatusModel

    public String icao24 {get;set;}

    public Integer firstSeen {get;set;}

    public String estDepartureAirport {get;set;}

    public Integer lastSeen {get;set;}

    public String estArrivalAirport {get;set;}

    public String callsign {get;set;}

    public Integer estDepartureAirportHorizDistance {get;set;}

    public Integer estDepartureAirportVertDistance {get;set;}

    public Integer estArrivalAirportHorizDistance {get;set;}

    public Integer estArrivalAirportVertDistance {get;set;}

    public Integer departureAirportCandidatesCount {get;set;}

    public Integer arrivalAirportCandidatesCount {get;set;}

    //---Use the JSON Deserialize

    public static List<OS_FlightStatusModel> parse(String json)

        return (List<OS_FlightStatusModel>) System.JSON.deserialize(json, List<OS_FlightStatusModel>.class);

有了上面的类，你就可以用一行代码轻松地解析 JSON：

//---Get the Flight Request

 private static List<OS_FlightStatusModel> getFlightRequest(String requestURL)

//---Return structure

List<OS_FlightStatusModel> retList = new List<OS_FlightStatusModel>();

//---Make the request

HttpResponse resp = getRequest( requestURL);

//---Check for Success

Integer respStatusCode = resp.getStatusCode();

if (respStatusCode == 200)

//---Read the Payload

String payload = resp.getBody();

debug('Payload: ' + payload);

//---Parse the payload

retList = OS_FlightStatusModel.parse(payload);

if (retList != null)

System.debug('Found ' + retList.size() + ' records');

for( OS_FlightStatusModel mRow : retList)

debug('Row: ' + mRow);

else

//---Handle an error

debug('Response Status Code: ' + respStatusCode);

return retList;

第 2 部分：动态 JSON 解析

对于更复杂的 JSON 结构，比如数组或嵌套对象，你可能需要使用动态 JSON 解析。这种做法需要更多行代码，并且要在 JSON 令牌之间小心地导航。虽然看起来更复杂，但在面对高级的 JSON 结构时，动态 JSON 解析是必要的。

示例：

/****************************************************************************************

* @Name OS_StateModelParser

* @Author Steve Simpson - steve@stevetecharc.com

* @Date 2023

* @Description Parser for reading State Models from JSON

****************************************************************************************

* Version Developer Date Description

*----------------------------------------------------------------------------------------

* 1.0 Steve Simpson 2023 Initial Creation

****************************************************************************************/

public with sharing class OS_StateModelParser extends OS_BaseParser

private OS_StateResponseModel responseModel {get; set;}

//--Parse the payload into the OS_StateResponseModel

public OS_StateResponseModel parse(String json)

//---Setup the return value

responseModel = new OS_StateResponseModel();

responseModel.States = new List<OS_StateModel>();

try

parseBody(json);

catch (Exception ex)

debug( 'Exception: ' + ex.getMessage() + ' ' + ex.getStackTraceString());

debugJSON(json);

return responseModel;

//---Parse the body of the JSON

private void parseBody(String json)

//---Set the default Page Size

if (PageSize == 0) PageSize = DEFAULT_PAGE_SIZE;

Boolean hasTokenTime = false;

Boolean hasTokenStates = false;

JSONParser parser = System.JSON.createParser(json);

//---Read Token by Token

while (parser.nextToken() != System.JSONToken.END_OBJECT)

//---Read the current Token, check its field name

if (parser.getCurrentToken() == System.JSONToken.FIELD_NAME)

String text = parser.getText();

debug( 'Json Token: ' + text);

//---If the next token has a value, then write it, this handles null values

if (parser.nextToken() != System.JSONToken.VALUE_NULL)

//---Read the time

if (text == 'time')

responseModel.ResponseTime = parser.getIntegerValue();

hasTokenTime = true;

//---Read the states

if (text == 'states')

responseModel.States = parseStateList(parser);

hasTokenStates = true;

//---If have both tags, then break out of loop

if (hasTokenStates && hasTokenTime) break;

//---Parse the States

private List<OS_StateModel> parseStateList(JSONParser parser)

CurrentRecord = 0;

//---Build the return list

List<OS_StateModel> retList = new List<OS_StateModel>();

//---Go to the next token if needed

if (parser.getCurrentToken() == null) parser.nextToken();

//---Iterate over the items

while (parser.nextToken() != System.JSONToken.END_ARRAY)

CurrentRecord++; //---Track the current record

String logLine = 'Rec: ' + CurrentRecord + ': ';

if (CurrentRecord > getMaxRecord())

//---If past the max record, then break out of loop

debug(logLine + 'End of page');

break;

else if (CurrentRecord >= getFirstRecordToProcess())

//---Build a new State Row

OS_StateModel sModel = new OS_StateModel();

parseStateItem(parser, sModel);

retList.add(sModel);

debug(logLine + 'State: ' + sModel);

else

//---Pass in null model to trigger token advancement without reading values

parseStateItem(parser, null);

debug(logLine + 'Skipped');

return retList;

//---Parse the States

private void parseStateItem(JSONParser parser, OS_StateModel sModel)

//---Go to the next token if needed

if (parser.getCurrentToken() == null) parser.nextToken();

Integer position = 0;

while (parser.nextToken() != System.JSONToken.END_ARRAY)

if (sModel != null && parser.getCurrentToken() != System.JSONToken.VALUE_NULL)

if (position == 0) sModel.icao24 = parser.getText();

if (position == 1) sModel.callsign = parser.getText();

if (position == 2) sModel.origin_country = parser.getText();

if (position == 3) sModel.time_position = parser.getIntegerValue();

if (position == 4) sModel.last_contact = parser.getIntegerValue();

if (position == 5) sModel.longitude = parser.getDoubleValue();

if (position == 6) sModel.latitude = parser.getDoubleValue();

if (position == 7) sModel.baro_altitude = parser.getDoubleValue();

if (position == 8) sModel.on_ground = parser.getBooleanValue();

if (position == 9) sModel.velocity = parser.getDoubleValue();

if (position == 10) sModel.true_track = parser.getDoubleValue();

if (position == 11) sModel.vertical_rate = parser.getDoubleValue();

if (position == 12)

//---Sensors, sub Array, should be null

if (position == 13) sModel.geo_altitude = parser.getDoubleValue();

if (position == 14) sModel.squawk = parser.getText();

if (position == 15) sModel.spi = parser.getBooleanValue();

if (position == 16) sModel.position_source = parser.getIntegerValue();

if (position == 17) sModel.category = parser.getIntegerValue();

position++;

//System.debug('Position ' + position);

第 3 部分：用自定义元数据进行动态映射

如果你需要更大的灵活性，可以考虑用自定义元数据进行动态映射。这种做法让你无需修改代码，就能把 JSON 字段动态地映射到 SObject 字段。有了动态映射，你可以随时添加或删除字段，在生产环境中提供极大的灵活性。

示例：

创建自定义元数据，把 JSON 字段映射到 SObject 的 API 名称、位置和数据类型。

加载自定义元数据，并用它动态地给 SObject 字段赋值。

/****************************************************************************************

* @Name OS_StateSObjectModelParser

* @Author Steve Simpson - steve@stevetecharc.com

* @Date 2023

* @Description Parser for reading State Models from JSON

****************************************************************************************

* Version Developer Date Description

*----------------------------------------------------------------------------------------

* 1.0 Steve Simpson 2023 Initial Creation

****************************************************************************************/

public with sharing class OS_StateSObjectModelParser extends OS_BaseParser

private OS_StateSObjectResponseModel responseModel {get; set;}

private List<OS_StateMap__mdt> mapList {get;set;}

//--Parse the payload into the OS_StateResponseModel

public OS_StateSObjectResponseModel parse(String json)

mapList = OS_StateMap__mdt.getAll().values();

//---Setup the return value

responseModel = new OS_StateSObjectResponseModel();

responseModel.States = new List<OS_State__c>();

try

parseBody(json);

catch (Exception ex)

debug( 'Exception: ' + ex.getMessage() + ' ' + ex.getStackTraceString());

debugJSON(json);

return responseModel;

//---Parse the body of the JSON

private void parseBody(String json)

//---Set the default Page Size

if (PageSize == 0) PageSize = DEFAULT_PAGE_SIZE;

Boolean hasTokenTime = false;

Boolean hasTokenStates = false;

JSONParser parser = System.JSON.createParser(json);

//---Read Token by Token

while (parser.nextToken() != System.JSONToken.END_OBJECT)

//---Read the current Token, check its field name

if (parser.getCurrentToken() == System.JSONToken.FIELD_NAME)

String text = parser.getText();

debug( 'Json Token: ' + text);

//---If the next token has a value, then write it, this handles null values

if (parser.nextToken() != System.JSONToken.VALUE_NULL)

//---Read the time

if (text == 'time')

responseModel.ResponseTime = parser.getIntegerValue();

hasTokenTime = true;

//---Read the states

if (text == 'states')

responseModel.States = parseStateList(parser);

hasTokenStates = true;

//---If have both tags, then break out of loop

if (hasTokenStates && hasTokenTime) break;

//---Parse the States

private List<OS_State__c> parseStateList(JSONParser parser)

CurrentRecord = 0;

//---Build the return list

List<OS_State__c> retList = new List<OS_State__c>();

//---Go to the next token if needed

if (parser.getCurrentToken() == null) parser.nextToken();

//---Iterate over the items

while (parser.nextToken() != System.JSONToken.END_ARRAY)

CurrentRecord++; //---Track the current record

String logLine = 'Rec: ' + CurrentRecord + ': ';

if (CurrentRecord > getMaxRecord())

//---If past the max record, then break out of loop

debug(logLine + 'End of page');

break;

else if (CurrentRecord >= getFirstRecordToProcess())

//---Build a new State Row

OS_State__c osState = new OS_State__c();

parseStateItem(parser, osState);

retList.add(osState);

debug(logLine + 'State: ' + osState);

else

//---Pass in null model to trigger token advancement without reading values

parseStateItem(parser, null);

debug(logLine + 'Skipped');

return retList;

//---Parse the States

private void parseStateItem(JSONParser parser, OS_State__c osState)

//---Go to the next token if needed

if (parser.getCurrentToken() == null) parser.nextToken();

Integer position = 0;

while (parser.nextToken() != System.JSONToken.END_ARRAY)

if (osState != null && parser.getCurrentToken() != System.JSONToken.VALUE_NULL)

OS_StateMap__mdt curMap = null;

for(OS_StateMap__mdt mapRow : mapList)

if (mapRow.Position__c == position)

curMap = mapRow;

break;

if (curMap != null)

String apiName = curMap.API_Name__c;

if (curMap.Data_Type__c == 'Text')

osState.put(apiName, parser.getText());

if (curMap.Data_Type__c == 'Integer')

osState.put(apiName, parser.getIntegerValue());

if (curMap.Data_Type__c == 'Double')

osState.put(apiName, parser.getDoubleValue());

if (curMap.Data_Type__c == 'Boolean')

osState.put(apiName, parser.getBooleanValue());

position++;

//System.debug('Position ' + position);

结论：

在 Salesforce Apex 外部调用中，你可以根据需要从多种 JSON 解析技术中选择。对于简单的静态 JSON，使用带单行反序列化的固定结构 JSON 解析。对于更复杂的结构，考虑动态 JSON 解析。而要获得最大的灵活性，就使用基于自定义元数据的动态映射。每种做法都有其适用场景，所以选择最符合你项目需求的那一种。

编码愉快！

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