Package groovy.json

Class 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
    • 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​(@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,
                         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