Package: groovy.json

## [Java] Class StreamingJsonBuilder

- groovy.json.StreamingJsonBuilder

- A builder for creating JSON payloads.

  This builder supports the usual builder syntax made of nested method calls and closures, but also some specific aspects of JSON data structures, such as list of values, etc. Please make sure to have a look at the various methods provided by this builder to be able to learn about the various possibilities of usage.

  Unlike the JsonBuilder class which creates a data structure in memory, which is handy in those situations where you want to alter the structure programatically before output, the StreamingJsonBuilder streams to a writer directly without any memory data structure. So if you don't need to modify the structure, and want a more memory-efficient approach, please use the StreamingJsonBuilder.

  Example:

           new StringWriter().with { w ->
               def builder = new groovy.json.StreamingJsonBuilder(w)
               builder.people {
                   person {
                       firstName 'Tim'
                       lastName 'Yates'
                       // Named arguments are valid values for objects too
                       address(
                           city: 'Manchester',
                           country: 'UK',
                           zip: 'M1 2AB',
                       )
                       living true
                       eyes 'left', 'right'
                   }
               }

               assert w.toString() == '{"people":{"person":{"firstName":"Tim","lastName":"Yates","address":{"city":"Manchester","country":"UK","zip":"M1 2AB"},"living":true,"eyes":["left","right"]}}}'
          }

  Authors:
    Tim Yates
    Andrey Bloschetsov
    Graeme Rocher
  Since:
    1.8.1

- - ### Nested Class Summary

    Nested classes
    Modifiers | Name | Description
    --- | --- | ---
    `static class` | `StreamingJsonBuilder.StreamingJsonDelegate` | The delegate used when invoking closures

  - ### Constructor Summary

    Constructors
    Constructor and description
    `StreamingJsonBuilder (Writer writer)` Instantiates a JSON builder.
    `StreamingJsonBuilder (Writer writer, Object content)` Instantiates a JSON builder, possibly with some existing data structure.

  - ### Methods Summary

    Methods
    Type Params | Return Type | Name and description
    --- | --- | ---
    `` | `Object` | `call(Map m)` Named arguments can be passed to the JSON builder instance to create a root JSON object
    `` | `void` | `call(String name)` The empty args call will create a key whose value will be an empty JSON object:
         new StringWriter().with { w ->
             def json = new groovy.json.StreamingJsonBuilder(w)
             json.person()
    `` | `Object` | `call(List l)` A list of elements as arguments to the JSON builder creates a root JSON array
    `` | `Object` | `call(Object... args)` Varargs elements as arguments to the JSON builder create a root JSON array
    `` | `Object` | `call(Iterable coll, Closure c)` A collection and closure passed to a JSON builder will create a root JSON array applying the closure to each object in the collection
    `` | `Object` | `call(Collection coll, Closure c)` Delegates to call(Iterable, Closure)
    `` | `Object` | `call(Closure c)` A closure passed to a JSON builder will create a root JSON object
    `` | `void` | `call(String name, Closure c)` A name and a closure passed to a JSON builder will create a key with a JSON object
    `` | `void` | `call(String name, Iterable coll, Closure c)` A name, a collection and closure passed to a JSON builder will create a root JSON array applying the closure to each object in the collection
    `` | `void` | `call(String name, Collection coll, Closure c)` Delegates to call(String, Iterable, Closure)
    `` | `void` | `call(String name, Map map, Closure callable)` If you use named arguments and a closure as last argument, the key/value pairs of the map (as named arguments) and the key/value pairs represented in the closure will be merged together — the closure properties overriding the map key/values in case the same key is used.
    `` | `Object` | `invokeMethod(String name, Object args)` A method call on the JSON builder instance will create a root object with only one key whose name is the name of the method being called.

  - ### Inherited Methods Summary

    Inherited Methods
    Methods inherited from class | Name
    --- | ---
    `class GroovyObjectSupport` | `getMetaClass, getProperty, invokeMethod, setMetaClass, setProperty`
    `class Object` | `wait, wait, wait, equals, toString, hashCode, getClass, notify, notifyAll`

- - ### Constructor Detail

    - #### public StreamingJsonBuilder(Writer writer)

      Instantiates a JSON builder.

      Parameters:
        `writer` - A writer to which Json will be written

    - #### public StreamingJsonBuilder(Writer writer, Object content)

      Instantiates a JSON builder, possibly with some existing data structure.

      Parameters:
        `writer` - A writer to which Json will be written
        `content` - a pre-existing data structure, default to null

  - ### Method Detail

    - #### public Object call(Map m)

      Named arguments can be passed to the JSON builder instance to create a root JSON object

      Example:

           new StringWriter().with { w ->
             def json = new groovy.json.StreamingJsonBuilder(w)
             json name: "Tim", age: 31

             assert w.toString() == '{"name":"Tim","age":31}'
           }

      Parameters:
        `m` - a map of key / value pairs
      Returns:
        a map of key / value pairs

    - #### public void call(String name)

      The empty args call will create a key whose value will be an empty JSON object:

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.person()

               assert w.toString() == '{"person":{}}'
           }

      throws:
        IOException
      Parameters:
        `name` - The name of the empty object to create

    - #### public Object call(List l)

      A list of elements as arguments to the JSON builder creates a root JSON array

      Example:

           new StringWriter().with { w ->
             def json = new groovy.json.StreamingJsonBuilder(w)
             def result = json([1, 2, 3])

             assert result == [ 1, 2, 3 ]
             assert w.toString() == "[1,2,3]"
           }

      Parameters:
        `l` - a list of values
      Returns:
        a list of values

    - #### public Object call(Object... args)

      Varargs elements as arguments to the JSON builder create a root JSON array

      Example:

           new StringWriter().with { w ->
             def json = new groovy.json.StreamingJsonBuilder(w)
             def result = json 1, 2, 3

             assert result instanceof List
             assert w.toString() == "[1,2,3]"
           }

      Parameters:
        `args` - an array of values
      Returns:
        a list of values

    - #### public Object call(Iterable coll, @DelegatesTo(StreamingJsonDelegate.class) Closure c)

      A collection and closure passed to a JSON builder will create a root JSON array applying the closure to each object in the collection

      Example:

           class Author {
                String name
           }
           def authors = [new Author (name: "Guillaume"), new Author (name: "Jochen"), new Author (name: "Paul")]

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json authors, { Author author ->
                   name author.name
               }

               assert w.toString() == '[{"name":"Guillaume"},{"name":"Jochen"},{"name":"Paul"}]'
           }

      Parameters:
        `coll` - a collection
        `c` - a closure used to convert the objects of coll

    - #### public Object call(Collection coll, @DelegatesTo(StreamingJsonDelegate.class) Closure c)

      Delegates to call(Iterable, Closure)

    - #### public Object call(@DelegatesTo(StreamingJsonDelegate.class) Closure c)

      A closure passed to a JSON builder will create a root JSON object

      Example:

           new StringWriter().with { w ->
             def json = new groovy.json.StreamingJsonBuilder(w)
             json {
                name "Tim"
                age 39
             }

             assert w.toString() == '{"name":"Tim","age":39}'
           }

      Parameters:
        `c` - a closure whose method call statements represent key / values of a JSON object

    - #### public void call(String name, @DelegatesTo(StreamingJsonDelegate.class) Closure c)

      A name and a closure passed to a JSON builder will create a key with a JSON object

      Example:

           new StringWriter().with { w ->
             def json = new groovy.json.StreamingJsonBuilder(w)
             json.person {
                name "Tim"
                age 39
             }

             assert w.toString() == '{"person":{"name":"Tim","age":39}}'
           }

      Parameters:
        `name` - The key for the JSON object
        `c` - a closure whose method call statements represent key / values of a JSON object

    - #### public void call(String name, Iterable coll, @DelegatesTo(StreamingJsonDelegate.class) Closure c)

      A name, a collection and closure passed to a JSON builder will create a root JSON array applying the closure to each object in the collection

      Example:

           class Author {
                String name
           }
           def authors = [new Author (name: "Guillaume"), new Author (name: "Jochen"), new Author (name: "Paul")]

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.people authors, { Author author ->
                   name author.name
               }

               assert w.toString() == '{"people":[{"name":"Guillaume"},{"name":"Jochen"},{"name":"Paul"}]}'
           }

      Parameters:
        `coll` - a collection
        `c` - a closure used to convert the objects of coll

    - #### public void call(String name, Collection coll, @DelegatesTo(StreamingJsonDelegate.class) Closure c)

      Delegates to call(String, Iterable, Closure)

    - #### public void call(String name, Map map, @DelegatesTo(StreamingJsonDelegate.class) Closure callable)

      If you use named arguments and a closure as last argument, the key/value pairs of the map (as named arguments) and the key/value pairs represented in the closure will be merged together — the closure properties overriding the map key/values in case the same key is used.

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.person(name: "Tim", age: 35) { town "Manchester" }

               assert w.toString() == '{"person":{"name":"Tim","age":35,"town":"Manchester"}}'
           }

      throws:
        IOException
      Parameters:
        `name` - The name of the JSON object
        `map` - The attributes of the JSON object
        `callable` - Additional attributes of the JSON object represented by the closure

    - #### public Object invokeMethod(String name, Object args)

      A method call on the JSON builder instance will create a root object with only one key whose name is the name of the method being called. This method takes as arguments:

      - a closure
      - a map (ie. named arguments)
      - a map and a closure
      - or no argument at all

      Example with a classical builder-style:

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.person {
                   name "Tim"
                    age 28
               }

               assert w.toString() == '{"person":{"name":"Tim","age":28}}'
           }

      Or alternatively with a method call taking named arguments:

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.person name: "Tim", age: 32

               assert w.toString() == '{"person":{"name":"Tim","age":32}}'
           }

      If you use named arguments and a closure as last argument, the key/value pairs of the map (as named arguments) and the key/value pairs represented in the closure will be merged together — the closure properties overriding the map key/values in case the same key is used.

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.person(name: "Tim", age: 35) { town "Manchester" }

               assert w.toString() == '{"person":{"name":"Tim","age":35,"town":"Manchester"}}'
           }

      The empty args call will create a key whose value will be an empty JSON object:

           new StringWriter().with { w ->
               def json = new groovy.json.StreamingJsonBuilder(w)
               json.person()

               assert w.toString() == '{"person":{}}'
           }

      Parameters:
        `name` - the single key
        `args` - the value associated with the key