Groovy example source code file (StreamingJsonBuilder.groovy)

This example Groovy source code file (StreamingJsonBuilder.groovy) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Groovy tags/keywords

closure, closure, expected, jsonexception, map, object, object, streamingjsonbuilder, streamingjsondelegate, streamingjsondelegate, writer, writer

The Groovy StreamingJsonBuilder.groovy source code

/*
 * Copyright 2003-2011 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package groovy.json

/**
 * A builder for creating JSON payloads.
 * <p>
 * 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.
 * <p>
 * Unlike the JsonBuilder class which creates a data structure in memory,
 * which is handy in those situations where you want to alter the structure programmatically before output,
 * the StreamingJsonBuilder streams to a writter 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.
 * <p>
 * Example:
 * <pre class="groovyTestCase">
 *     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"]}}}'
 *    }
 * </pre>
 *
 * @author Tim Yates
 * @since 1.8.1
 */
class StreamingJsonBuilder {

    Writer writer
    
    /**
     * Instantiates a JSON builder, possibly with some existing data structure.
     *
     * @param writer A writer to which Json will be written
     * @param content a pre-existing data structure, default to null
     */
    StreamingJsonBuilder( Writer writer, content = null) {
        this.writer = writer
        if( content ) writer.write( JsonOutput.toJson( content ) )
    }

    /**
     * Named arguments can be passed to the JSON builder instance to create a root JSON object
     * <p>
     * Example:
     * <pre class="groovyTestCase">
     * new StringWriter().with { w ->
     *   def json = new groovy.json.StreamingJsonBuilder( w )
     *   json name: "Tim", age: 31
     *
     *   assert w.toString() == '{"name":"Tim","age":31}'
     * }
     * </pre>
     *
     * @param m a map of key / value pairs
     * @return a map of key / value pairs
     */
    def call(Map m) {
        writer.write JsonOutput.toJson( m )
        return m
    }

    /**
     * A list of elements as arguments to the JSON builder creates a root JSON array
     * <p>
     * Example:
     * <pre class="groovyTestCase">
     * 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]"
     * }
     * </pre>
     *
     * @param l a list of values
     * @return a list of values
     */
    def call(List l) {
        writer.write( JsonOutput.toJson( l ) )
        return l
    }

    /**
     * Varargs elements as arguments to the JSON builder create a root JSON array
     * <p>
     * Example:
     * <pre class="groovyTestCase">
     * 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]"
     * }
     * </pre>

     * @param args an array of values
     * @return a list of values
     */
    def call(Object... args) {
        def l = args.toList()
        writer.write JsonOutput.toJson( l )
        return l
    }

    /**
     * A closure passed to a JSON builder will create a root JSON object
     * <p>
     * Example:
     * <pre class="groovyTestCase">
     * new StringWriter().with { w ->
     *   def json = new groovy.json.StreamingJsonBuilder( w )
     *   json {
     *      name "Tim"
     *      age 39
     *   }
     *
     *   assert w.toString() == '{"name":"Tim","age":39}'
     * }
     * </pre>
     *
     * @param c a closure whose method call statements represent key / values of a JSON object
     */
    def call(Closure c) {
        writer.write( '{' )
        StreamingJsonDelegate.cloneDelegateAndGetContent( writer, c )
        writer.write( '}' )
    }

    /**
     * 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:
     * <ul>
     *     <li>a closure
     *     <li>a map (ie. named arguments)
     *     <li>a map and a closure
     *     <li>or no argument at all
     * </ul>
     * <p>
     * Example with a classicala builder-style:
     * <pre class="groovyTestCase">
     * 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}}'
     * }
     * </pre>
     *
     * Or alternatively with a method call taking named arguments:
     * <pre class="groovyTestCase">
     * 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}}'
     * }
     * </pre>
     *
     * 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.
     * <pre class="groovyTestCase">
     * 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"}}'
     * }
     * </pre>
     *
     * The empty args call will create a key whose value will be an empty JSON object:
     * <pre class="groovyTestCase">
     * new StringWriter().with { w ->
     *     def json = new groovy.json.StreamingJsonBuilder( w )
     *     json.person()
     *
     *     assert w.toString() == '{"person":{}}'
     * }
     * </pre>
     *
     * @param name the single key
     * @param args the value associated with the key
     */
    def invokeMethod(String name, Object args) {
        if (args?.size() == 0) {
            writer.write JsonOutput.toJson( [(name): [:]] )
        } else if (args?.size() == 1) {
            if (args[0] instanceof Closure) {
                writer.write "{${JsonOutput.toJson( name )}:"
                this.call( args[0] )
                writer.write '}'
            } else if (args[0] instanceof Map) {
                writer.write JsonOutput.toJson( [(name): args[0]] )
            }
            else {
                throw new JsonException("Expected no arguments, a single map, a single closure, or a map and closure as arguments.")
            }
        } else if (args?.size() == 2 && args[0] instanceof Map && args[1] instanceof Closure) {
            writer.write "{${JsonOutput.toJson( name )}:{"
            args[0].eachWithIndex { it, idx ->
                if( idx > 0 ) writer.write ','
                writer.write JsonOutput.toJson( it.key )
                writer.write ':'
                writer.write JsonOutput.toJson( it.value )
            }
            StreamingJsonDelegate.cloneDelegateAndGetContent( writer, args[1], !args[0].size() )
            writer.write '}}'
        }
        else {
            throw new JsonException("Expected no arguments, a single map, a single closure, or a map and closure as arguments.")
        }
    }
}

class StreamingJsonDelegate {
    Writer writer
    boolean first
    
    StreamingJsonDelegate( Writer w, boolean first ) {
        this.writer = w
        this.first = first
    }
    
    def invokeMethod(String name, Object args) {
        if (args) {
            if( !first ) {
                writer.write ','
            }
            writer.write JsonOutput.toJson( name )
            writer.write ':'
            writer.write JsonOutput.toJson( args.size() == 1 ? args[0] : args.toList() )
            first = false
        }
    }

    static cloneDelegateAndGetContent(Writer w, Closure c, boolean first=true ) {
        def delegate = new StreamingJsonDelegate( w, first )
        Closure cloned = c.clone()
        cloned.delegate = delegate
        cloned.resolveStrategy = Closure.DELEGATE_FIRST
        cloned()
    }
}