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

Author:

Tim Yates, Andrey Bloschetsov, Graeme Rocher

Nested Class Summary

Nested Classes

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

Constructor Summary

Constructors

Constructor and Description
StreamingJsonBuilder(java.io.Writer writer) Instantiates a JSON builder.
StreamingJsonBuilder(java.io.Writer writer, java.lang.Object content) Instantiates a JSON builder, possibly with some existing data structure.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	call(Closure c) A closure passed to a JSON builder will create a root JSON object
java.lang.Object	call(java.util.Collection coll, Closure c) Delegates to call(Iterable, Closure)
java.lang.Object	call(java.lang.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
java.lang.Object	call(java.util.List l) A list of elements as arguments to the JSON builder creates a root JSON array
java.lang.Object	call(java.util.Map m) Named arguments can be passed to the JSON builder instance to create a root JSON object
java.lang.Object	call(java.lang.Object... args) Varargs elements as arguments to the JSON builder create a root JSON array
void	call(java.lang.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":{}}' }
void	call(java.lang.String name, Closure c) A name and a closure passed to a JSON builder will create a key with a JSON object
void	call(java.lang.String name, java.util.Collection coll, Closure c) Delegates to call(String, Iterable, Closure)
void	call(java.lang.String name, java.lang.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(java.lang.String name, java.util.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.
java.lang.Object	invokeMethod(java.lang.String name, java.lang.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, getProperty, setMetaClass, setProperty

Methods inherited from class java.lang.Object

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

Constructor Detail

StreamingJsonBuilder

public StreamingJsonBuilder(java.io.Writer writer)

Instantiates a JSON builder.

Parameters:

writer - A writer to which Json will be written

StreamingJsonBuilder

public StreamingJsonBuilder(java.io.Writer writer,
                            java.lang.Object content)
                     throws java.io.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:

java.io.IOException

Method Detail

call

public java.lang.Object call(java.util.Map m)
                      throws java.io.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:

java.io.IOException

call

public void call(java.lang.String name)
          throws java.io.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:

java.io.IOException

call

public java.lang.Object call(java.util.List l)
                      throws java.io.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:

java.io.IOException

call

public java.lang.Object call(java.lang.Object... args)
                      throws java.io.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:

java.io.IOException

call

public java.lang.Object call(java.lang.Iterable coll,
                             @DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                             Closure c)
                      throws java.io.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:

java.io.IOException

call

public java.lang.Object call(java.util.Collection coll,
                             @DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                             Closure c)
                      throws java.io.IOException

Delegates to call(Iterable, Closure)

Throws:

java.io.IOException

call

public java.lang.Object call(@DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                             Closure c)
                      throws java.io.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:

java.io.IOException

call

public void call(java.lang.String name,
                 @DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                 Closure c)
          throws java.io.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:

java.io.IOException

call

public void call(java.lang.String name,
                 java.lang.Iterable coll,
                 @DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                 Closure c)
          throws java.io.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:

java.io.IOException

call

public void call(java.lang.String name,
                 java.util.Collection coll,
                 @DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                 Closure c)
          throws java.io.IOException

Delegates to call(String, Iterable, Closure)

Throws:

java.io.IOException

call

public void call(java.lang.String name,
                 java.util.Map map,
                 @DelegatesTo(value=StreamingJsonBuilder.StreamingJsonDelegate.class)
                 Closure callable)
          throws java.io.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:

java.io.IOException

invokeMethod

public java.lang.Object invokeMethod(java.lang.String name,
                                     java.lang.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":{}}'
 }
 

Specified by:

invokeMethod in interface GroovyObject

Overrides:

invokeMethod in class GroovyObjectSupport

Parameters:

name - the single key

args - the value associated with the key

Returns:

the result of invoking the method