Package groovy.json

Class StreamingJsonBuilder

java.lang.Object

groovy.lang.GroovyObjectSupport

groovy.json.StreamingJsonBuilder

All Implemented Interfaces:

GroovyObject

public class StreamingJsonBuilder
extends GroovyObjectSupport

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"]}}}'
    }
 

Since:

1.8.1

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	StreamingJsonBuilder.StreamingJsonDelegate	The delegate used when invoking closures

Constructor Summary

Constructors

Constructor	Description
StreamingJsonBuilder(Writer writer)	Instantiates a JSON builder.
StreamingJsonBuilder(Writer writer, JsonGenerator generator)	Instantiates a JSON builder with the given generator.
StreamingJsonBuilder(Writer writer, Object content)	Instantiates a JSON builder, possibly with some existing data structure.
StreamingJsonBuilder(Writer writer, Object content, JsonGenerator generator)	Instantiates a JSON builder, possibly with some existing data structure and the given generator.

Method Summary

Modifier and Type	Method	Description
Object	call(Closure c)	A closure passed to a JSON builder will create a root JSON object
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(Object... args)	Varargs elements as arguments to the JSON builder create a root JSON array
void	call(String name)	The empty args call will create a key whose value will be an empty 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	call(Collection coll, Closure c)	Delegates to call(Iterable, Closure)
Object	call(List l)	A list of elements as arguments to the JSON builder creates a root JSON array
Object	call(Map m)	Named arguments can be passed to the JSON builder instance to create a root JSON object
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.

Methods inherited from class groovy.lang.GroovyObjectSupport

getMetaClass, setMetaClass

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface groovy.lang.GroovyObject

getProperty, setProperty

Constructor Detail

StreamingJsonBuilder

public StreamingJsonBuilder(Writer writer)

Instantiates a JSON builder.

Parameters:

writer - A writer to which Json will be written

StreamingJsonBuilder

public StreamingJsonBuilder(Writer writer,
                            JsonGenerator generator)

Instantiates a JSON builder with the given generator.

Parameters:

writer - A writer to which Json will be written

generator - used to generate the output

Since:

2.5.0

StreamingJsonBuilder

public StreamingJsonBuilder(Writer writer,
                            Object content)
                     throws IOException

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

Throws:

IOException

StreamingJsonBuilder

public StreamingJsonBuilder(Writer writer,
                            Object content,
                            JsonGenerator generator)
                     throws IOException

Instantiates a JSON builder, possibly with some existing data structure and the given generator.

Parameters:

writer - A writer to which Json will be written

content - a pre-existing data structure, default to null

generator - used to generate the output

Throws:

IOException

Since:

2.5.0

Method Detail

call

public Object call(Map m)
            throws IOException

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

Throws:

IOException

call

public void call(String name)
          throws IOException

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 name of the empty object to create

Throws:

IOException

call

public Object call(List l)
            throws IOException

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

Throws:

IOException

call

public Object call(Object... args)
            throws IOException

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

Throws:

IOException

call

public Object call(Iterable coll,
                   @DelegatesTo(StreamingJsonDelegate.class)
                   Closure c)
            throws IOException

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

Throws:

IOException

call

public Object call(Collection coll,
                   @DelegatesTo(StreamingJsonDelegate.class)
                   Closure c)
            throws IOException

Delegates to call(Iterable, Closure)

Throws:

IOException

call

public Object call(@DelegatesTo(StreamingJsonDelegate.class)
                   Closure c)
            throws IOException

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

Throws:

IOException

call

public void call(String name,
                 @DelegatesTo(StreamingJsonDelegate.class)
                 Closure c)
          throws IOException

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

Throws:

IOException

call

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

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

Throws:

IOException

call

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

Delegates to call(String, Iterable, Closure)

Throws:

IOException

call

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

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"}}'
 }
 

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

Throws:

IOException

invokeMethod

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

Returns:

the result of invoking the method