Salesforce JSON解析

前言

JSON（JavaScript Object Notation）格式是目前比较流行的一种数据传输方式。JSON是一种轻量级的数据传输方式（尤其相对于XML方式），而且采用JSON传输数据结构清晰，易于理解和解析。在Salesforce中大部分的数据传输都可以采用JSON（SOAP/Metadata部分强制需要XML），所以有必要去了解Salesforce对于JSON的支持力度。

相关类

1. JSONParser：需要实例，以调用相应的方法。主要功能是将JSON字符串转化为对象，并提供可读取为Apex基本类型/Apex Object方法，例如：getDateValue()；
2. JSONGenerator：需要实例，以调用相应的方法。主要功能是将Apex对象等转化为JSON字符串，提供Step By Step写入，例如：writeTimeField()；
3. JSON：静态方法，不需要实例。一个强大的Super（效果相当于，并不是技术实现），提供了JSONParser/JSONGenerator实例方法。并提供将Apex对象转为JSON字符串/JSON字符串转为Apex Object/Collection（List/Map等）；
4. JSONToken：枚举类型。主要服务于JSONParser

下面是一段JSON数据，我们尝试用不同的方式解析/组装：

{    "messages": [        {            "type": "Availability",            "message": {                "results": [                    {                        "id": "5732800000005GQ",                        "isAvailable": true                    }                ]            }        }    ]}

解析

以获得results中isAvailable值为例：

1. JSONParser
   

   String jsonS = '{"messages":[{"type":"Availability","message":{"results":[{"id":"5732800000005GQ","isAvailable":true}]}}]}';JSONParser parser = JSON.createParser(jsonS);while (parser.nextToken() != null) {if(parser.getCurrentToken() == JSONToken.FIELD_NAME && parser.getText() == 'isAvailable') {parser.nextValue();System.debug('-- isAvailable: ' + parser.getBooleanValue());}}

2. JSON
   

   String jsonS = '{"messages":[{"type":"Availability","message":{"results":[{"id":"5732800000005GQ","isAvailable":true}]}}]}';Map<String, Object> obj = (Map<String, Object>)JSON.deserializeUntyped(jsonS);List<Object> messages = (List<Object>)obj.get('messages');for(Object o : messages) {Map<String, Object> messageO = (Map<String, Object>)o;Map<String, Object> message = (Map<String, Object>)messageO.get('message');List<Object> results = (List<Object>)message.get('results');for(Object r : results) {Map<String, Object> result = (Map<String, Object>)r;System.debug('-- isAvailable: ' + result.get('isAvailable'));}}

以上代码是一种简单的解析，不涉及直接解析为Class。直观的比较而言似乎JSONParser解析要比JSON更简单、方便一些，JSON的解析方式涉及到的类型转化很多、很繁琐，一不小心就得不到想要的结果。实际上JSONParser的解析方式如果我们想要直接得到某个属性而不考虑其他，确实很快很便捷。但是却受到两个重要的限制：

1. Key是否有重复（在JSON对象中我们很容易在不同的层级中设置相同的Key），若是这样我们可能得到错误的值；
2. 没有层级结构：解析的结果我们无法完全的获悉层次结构。

它的优势也很明显，可以直接获取到属性值并且获得相应的类型（除String，获取String要使用getBlobValue()）。JSON的解析方式看起来确实复杂而且实际执行也较为复杂，但却有个优势就是可以获得层级结构，并轻松的转为相应的Map（前提是解析过程已有）。

序列化

我们同样以构造出上述的结构为例：

1. JSONGenerator
   

   JSONGenerator generator = JSON.createGenerator(true);generator.writeStartObject();generator.writeFieldName('messages');generator.writeStartArray();generator.writeStartObject();generator.writeObjectField('type', 'Availability');generator.writeFieldName('message');generator.writeStartObject();generator.writeFieldName('results');generator.writeStartArray();generator.writeStartObject();generator.writeObjectField('id', '5732800000005GQ');generator.writeObjectField('isAvailable', true);generator.writeEndObject();generator.writeEndArray();generator.writeEndObject();generator.writeEndObject();generator.writeEndArray();generator.writeEndObject();System.debug(generator.getAsString());

   
   
2. JSON
   

   Map<String, Object> result = new Map<String, Object>();result.put('id', '5732800000005GQ');result.put('isAvailable', true);List<Map<String, Object>> results = new List<Map<String, Object>>();results.add(result);Map<String, Object> message = new Map<String, Object>();message.put('type', 'Availability');message.put('message', results);List<Object> messagesL = new List<Object>();messagesL.add(message);Map<String, Object> messages = new Map<String, Object>();messages.put('messages', messagesL);System.debug(JSON.serializePretty(messages));

以上代码简单的构建了一个JSON字符串。通过代码可以看到JSONGenerator构建方式是由上之下，一级一级搭建层级结构，整个过程可控但稍显臃肿；JSON的方式是先构建相应的对象（这里由Map/List实现）,在转化为JSON字符串，层级结构由对象结构决定（由于Map无序，不保证同级顺序），转化方式较为简洁。以上方式不涉及直接转化Object，只涉及基本字段和Array。

心得

1. JSON的解析和转化在Salesforce内相对而言较为简单，根据需求不同提供不同的解决方式（过程时候可控）；
2. 在涉及到解析较为严谨的地方（例如接口数据等）建议转化为对应的Object，而不是Map；
3. JSON中带有Pretty的方法是输出是否缩进；
4. 在实际过程中，笔者较多的使用JOSN Class的解析和转化方式，解析直接，转化方便；
5. JSON解析为Object的情况下：两种解析方式均提供了带有Strict方法（是否严格匹配）。

附录

各自的方法和属性：

• JSON
  • createGenerator(prettyPrint): Returns a new JSON generator;
    
  • createParser(jsonString): Returns a new JSON parser;
    
  • deserialize(jsonString, apexType): Deserializes the specified JSON string into an Apex object of the specified type;
    
  • deserializeStrict(jsonString, apexType): Deserializes the specified JSON string into an Apex object of the specified type;
    
  • deserializeUntyped(jsonString): Deserializes the specified JSON string into collections of primitive data types;
    
  • serialize(objectToSerialize): Serializes Apex objects into JSON content;
    
  • serializePretty(objectToSerialize): Serializes Apex objects into JSON content and generates indented content using the pretty-print format.
    
• JSONGenerator
  
  • close(): Closes the JSON generator;
  • getAsString()Returns the generated JSON content.
  • isClosed()Returns true if the JSON generator is closed; otherwise, returns false.
  • writeBlob(blobValue)Writes the specified Blob value as a base64-encoded string.
  • writeBlobField(fieldName, blobValue)Writes a field name and value pair using the specified field name and BLOB value.
  • writeBoolean(blobValue)Writes the specified Boolean value.
  • writeBooleanField(fieldName, booleanValue)Writes a field name and value pair using the specified field name and Boolean value.
  • writeDate(dateValue)Writes the specified date value in the ISO-8601 format.
  • writeDateField(fieldName, dateValue)Writes a field name and value pair using the specified field name and date value. The date value is written in the ISO-8601 format.
  • writeDateTime(datetimeValue)Writes the specified date and time value in the ISO-8601 format.
  • writeDateTimeField(fieldName, datetimeValue)Writes a field name and value pair using the specified field name and date and time value. The date and time value is written in theISO-8601 format.
  • writeEndArray()Writes the ending marker of a JSON array (']').writeEndObject()Writes the ending marker of a JSON object ('}').
  • writeFieldName(fieldName)Writes a field name.writeId(identifier)Writes the specified ID value.
  • writeIdField(fieldName, identifier)Writes a field name and value pair using the specified field name and identifier value.
  • writeNull()Writes the JSON null literal value.
  • writeNullField(fieldName)Writes a field name and value pair using the specified field name and the JSON null literal value.
  • writeNumber(number)Writes the specified decimal value.writeNumber(number)Writes the specified double value.
  • writeNumber(number)Writes the specified integer value.writeNumber(number)Writes the specified long value.
  • writeNumberField(fieldName, number)Writes a field name and value pair using the specified field name and decimal value.
  • writeNumberField(fieldName, number)Writes a field name and value pair using the specified field name and double value.
  • writeNumberField(fieldName, number)Writes a field name and value pair using the specified field name and integer value.
  • writeNumberField(fieldName, number)Writes a field name and value pair using the specified field name and long value.
  • writeObject(anyObject)Writes the specified Apex object in JSON format.
  • writeObjectField(fieldName, value)Writes a field name and value pair using the specified field name and Apex object.
  • writeStartArray()Writes the starting marker of a JSON array ('[').writeStartObject()Writes the starting marker of a JSON object ('{').
  • writeString(stringValue)Writes the specified string value.writeStringField(fieldName, stringValue)Writes a field name and value pair using the specified field name and string value.
  • writeTime(timeValue)Writes the specified time value in the ISO-8601 format.
  • writeTimeField(fieldName, timeValue)Writes a field name and value pair using the specified field name and time value in the ISO-8601 format.
    
• JSONParser
  • clearCurrentToken()Removes the current token.
  • getBlobValue()Returns the current token as a BLOB value.
  • getBooleanValue()Returns the current token as a Boolean value.
  • getCurrentName()Returns the name associated with the current token.
  • getCurrentToken()Returns the token that the parser currently points to or null if there's no current token.
  • getDatetimeValue()Returns the current token as a date and time value.
  • getDateValue()Returns the current token as a date value.getDecimalValue()Returns the current token as a decimal value.
  • getDoubleValue()Returns the current token as a double value.getIdValue()Returns the current token as an ID value.
  • getIntegerValue()Returns the current token as an integer value.
  • getLastClearedToken()Returns the last token that was cleared by the clearCurrentToken method.
  • getLongValue()Returns the current token as a long value.
  • getText()Returns the textual representation of the current token or null if there's no current token.
  • getTimeValue()Returns the current token as a time value.
  • hasCurrentToken()Returns true if the parser currently points to a token; otherwise, returns false.
  • nextToken()Returns the next token or null if the parser has reached the end of the input stream.
  • nextValue()Returns the next token that is a value type or null if the parser has reached the end of the input stream.
  • readValueAs(apexType)Deserializes JSON content into an object of the specified Apex type and returns the deserialized object.
  • readValueAsStrict(apexType)Deserializes JSON content into an object of the specified Apex type and returns the deserialized object. All attributes in the JSONcontent must be present in the specified type.
  • skipChildren()Skips all child tokens of type JSONToken.START_ARRAY and JSONToken.START_OBJECT that the parser currentlypoints to.
    
• JSONToken
  • END_ARRAY: The ending of an object value. This token is returned when '}' isencountered.
  • END_OBJECTFIELD_NAME: A string token that is a field name.
  • NOT_AVAILABLE:  The requested token isn't available.The start of an array value. This token is returned when '[' isencountered.
  • START_ARRAY: The start of an object value. This token is returned when '{' isencountered.
  • START_OBJECT: An embedded object that isn't accessible as a typical objectstructure that includes the start and end object tokens START_OBJECT and END_OBJECT but is represented as a raw object.
  • VALUE_EMBEDDED_OBJECTVALUE_FALSE: The literal “false” value.
  • VALUE_NULL:  The literal “null” value.
  • VALUE_NUMBER_FLOAT:  A float value.
  • VALUE_NUMBER_INT:  An integer value.1830Reference JSONToken EnumEnum Value Description
  • VALUE_STRING:  A string value.
  • VALUE_TRUE:  A value that corresponds to the “true” string literal.

参考

https://resources.docs.salesforce.com/208/latest/en-us/sfdc/pdf/salesforce_apex_language_reference.pdf