Transcript Json - Java.net

JSON Pointer and JSON Patch
Updates to Java API for JSON Processing
Kin-man Chung
Oracle Corporation
September 30, 2014
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3
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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4
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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5
JSON Object Model Overview
JsonValue
• An immutable representation of a JSON value
• Represented by:
– JsonObject
– JsonArray
– JsonNumber
– JsonString
– Literals
• TRUE, FALSE, and NULL
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6
JSON Object Model Overview
JsonObject
• Represents a JSON object
• java.util.Map<String, JsonValue>
• Created with
– JsonObjectBuilder
– JsonObjectReader
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7
JSON Object Model Overview
JsonArray
• Represents a JSON array
• java.util.List<JsonValue>
• Created with
– JsonArrayBuilder
– JsonArrayReader
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8
JSON Object Model Overview
Json
• Factory class for creating JSON objects
• Plugin factories with service provider
• API includes
– createObjectBuilder()
– createArrayBuilder()
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9
Example: contacts in JSON
[
]
{
"name": "Duke",
"gender": "M",
"phone": {
"areacode": "650",
"number": "234-5678"}
},
{
"name": "Jane",
”gender": "F",
"phone": {
"areacode": "777",
"number": "999-5555"}
},
{
"name": "Amy",
"gender": "F",
"phone": {
"areacode": "505"
"number": "333-4444"}
}
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10
Example: contacts in JSON object model
JsonArray contacts = Json.createArrayBuilder()
.add(Json.createObjectBuilder()
.add("name", "Duke")
.add("gender", "M")
.add("phone", Json.createObjectBuilder()
.add("areacode", "650")
.add("number", "234-5678")))
.add(Json.createObjectBuilder()
.add("name", "Jane")
.add("gender", "F")
.add("phone", Json.createObjectBuilder()
.add("areacode", ”777")
.add("number": "999-5555")))
.add(Json.createObjectBuilder()
.add("name", “Amy")
.add("gender", "F")
.add("phone", Json.createObjectBuilder()
.add("areacode", "505")
.add("number", "333-4444")))
.build();
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11
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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12
JSON Pointer
• Specified in RFC 6901
• A string syntax for referencing a JSON value
• Example
– /0/phone/number
• refers to the phone number of first person in the contacts
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13
JSON Pointer
Proposed API
JsonArray contacts = Json.createArrayBuilder().add(…).build();
// Create a JsonPointer
JsonPointer p = Json.createPointer("/0/phone/number");
// Get the value at the referenced location in the target
JsonValue v = p.getValue(contacts);
// Replace a value at the referenced location, returning a new array
// with the change
JsonArray result = p.replace(contacts, "123-4567");
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14
JSON Pointer
Methods in JsonPointer
• getValue
– Get the value at the referenced location
• add
– Add/insert a value at the referenced location
• replace
– Replace a value at the referenced location
• remove
– Remove a value at the referenced location
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15
JSON Pointer
Operations in JsonPointer
• An operation is applied to a JsonArray or JsonObject
• Operations do not modify the target JsonArray or JsonObject
• Operation add, replace, or remove returns a new JsonArray or JsonObject
containing the result
– Transforms the target into the result
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16
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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17
JSON Patch
• Specified in RFC 6902
• Sequence of operations for modifying a JSON document
– Operations specified in a JSON array
• Suitable for use in http PATCH method
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18
JSON Patch
Example
[
{"op":"replace", "path":"/1/phone", "value": {
"areacode": "111",
"number": "222-3333"}
}
{"from":"/1/phone", "path": "/2", "op":"copy"}
]
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19
JSON Patch
Operations
• An patch operation is a JSON object
• Must have an “op” field with a value of
– “add”, “replace”, “remove”, “move”, “copy”, or “test”
• Must have a “path” field
– A JSON Pointer specifying the target location
• Other fields depending on “op”
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20
JSON Patch
Proposed API
// Create the target and the patch
JsonArray target = Json.createArrayBuilder().add(…).build();
JsonArray patch = Json.createArrayBuilder()… .build();
// Create JsonPatch from patch
JsonPatch jsonpatch = Json.createPatch(patch);
// Apply the patch to the target and return the result
JsonArray result = jsonpatch.apply(target);
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21
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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22
JSON Editing/Transformation
• A JSON Patch transforms a JSON target to a JSON result
• Propose adding capability to edit a JsonArray or JsonObject
• Use builder pattern:
– Create builders with initial JsonArray or JsonObject
– Add to ObjectBuilder
• remove(name)
– Add to ArrayBuilder
• add(index, value), set(index, value), remove(index)
– Builder returns immutable JsonArray or JsonObject when done
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23
JSON Editing
Proposed API
// Create the target
JsonArray target = Json.createArrayBuilder().add(…).build();
// Create a builder initialized with the target
JsonArrayBuilder builder = Json.createArrayBuilder(target);
// Creates a new object and insert it into the array
JsonObject John = Json.createObjectBuilder()… .build();
JsonArray result = builder.add(1, John)
.build();
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24
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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25
JSON Query with Java SE 8
• A JsonObject is a Map, and a JsonArray is a List, so queries can be
implemented with Java’s stream operations, using Lambda expressions
• Example: Output names of contacts whose gender is F
JsonArray contacts;
contacts.getValuesAs(JsonObject.class).stream()
.filter(x->"F".equals(x.getString("gender")))
.map(x->x.getString("name"))
.forEach(System.out::println);
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26
JSON Query with Java SE 8
• Example: Collect query results in a List
JsonArray contacts;
List<String> names =
contacts.getValuesAs(JsonObject.class).stream()
.filter(x->"F".equals(x.getString("gender")))
.map(x->x.getString(“name”))
.collect(Collectors.toList());
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27
JSON Query with Java SE 8
Problem
• Java Collectors return Lists or Maps.
• We need collectors that returns JsonArrays or JsonObjects
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JSON Query with Java SE 8
Proposed API
• New helper class JsonCollectors that construct Collectors for JSON objects
or arrays
• toJsonArray:
– Accumulates values in a JsonArray
• toJsonObject:
– Accumulates values in a JsonObject
• groupBy
– Implements “group by” operations on the values
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29
JSON Query with Java SE 8
Example
• Collect the query result in a JsonArray
JsonArray contacts;
JsonArray names =
contacts.getValuesAs(JsonObject.class).stream()
.filter(x->"F".equals(x.getString("gender")))
.map(x->x.getString("name"))
.collect(JsonCollectors.toJsonArray());
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30
JSON Query with Java SE 8
Example
• Collect the query result in a JsonObject
JsonArray contacts;
JsonObject nameToPhones =
contacts.getValuesAs(JsonObject.class).stream()
.filter(x->"F".equals(x.getString("gender")))
.collect(JsonCollectors.toJsonObject(
x->x.getString("name"),
x->x.getJsonObject("phone"));
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31
JSON Query with Java SE 8
Example
• Group the contacts by gender
JsonArray contacts;
JsonObject groups =
contacts.getValuesAs(JsonObject.class).stream()
.collect(JsonCollectors.groupBy(x->getString("gender")));
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32
JSON Query with Java SE 8
Example: Putting it all together
• Change the phone areacodes from “415” to “650”
Static int index = -1;
JsonArray patch = contacts.getValuesAs(JsonObject.class).stream()
.peek(x->index++)
.filter(x->x.getObject("phone").getString("areacode").equals("415"))
.map(Json.createObjectBuilder()
.add("op", "replace")
.add("path", "/"+index+"/phone/areacode")
.add("value", “650”)
.build())
.collect(JsonCollectors.toJsonArray());
JsonArray result = Json.createPatch(patch).apply(contacts);
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33
Program Agenda
1
JSON Object Model Overview
2
JSON Pointer
3
JSON Patch
4
JSON Editing/Transformation
5
JSON Query with Java SE 8
6
Big JSON data
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34
Support for big JSON data
• Big JSON data
– Cannot fit in memory
– Generated dynamically
– Potentially infinite
• We already have a stream model, suitable for processing big data
– Add API to make it more useful
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35
Support for big JSON data
• Allow creation of partial JSON data in JsonParser
– Add getJsonObject() at the beginning of an object
– Add getJsonArray() at the beginning of an array
• Allow skipping values in JsonParser
• API for getting java.util.stream in JsonParser
– Lazy evaluation, pull model
– Low level: Stream of parse events
– High level: Stream of JsonObject and JsonArray elements
• Performance matters
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Summary
• Support for JSON Pointer and JSON Patch
• Add editing/transformation to JsonObject and JsonArray
• Add help class/method for JSON query
• Add support for big JSON data
• WARNING: The API changes are just proposals, are not final
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37
Q&A
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