Problem creating JSON with JsonGroovyBuilder in Groovy - json

Question

I am new to JSON and Groovy. I can make an AJAX call to a groovlet and make it build some HTML codes with MarkupBuilder. Along with the HTML string being returned, I want a JSON string to be filled in one of a input text box. The problem is the use of JsonGroovyBuilder(). I can't even get the simplest example shown in Json-lib to run correctly. Here is my code:
import net.sf.json.groovy.*;
import net.sf.json.groovy.JsonGroovyBuilder;
def builder = new JsonGroovyBuilder()
def books = builder.books {
book = [title: "Groovy in Action", author: "Dierk Konig"]
book = [title: "Groovy in Action", author: "Dierk Konig"]
}
I run this simple piece of code on GroovyConsole and I get this in return:
Result: {"books":null}
Very odd. But the even "odder" thing is when I run it in Eclipse, I get this:
Caught: groovy.lang.MissingMethodException: No signature of method: net.sf.json.groovy.JsonGroovyBuilder.books() is applicable for argument types: (JSONSandbox$_run_closure1) values: [JSONSandbox$_run_closure1#164debb]
Possible solutions: is(java.lang.Object)
at JSONSandbox.run(JSONSandbox.groovy:6)
I think that I have all the jar files I needed:
json-lib-2.3-jdk15.jar
commons-collections-2.1.jar
commons-lang-2.3.jar
httpclient-4.0.1.jar
I have been stuck in this problem for a couple of days now. Perhaps I have done something wrong, or misunderstanding the use of this function. Everywhere I search on JSON and Groovy points back to Grails. I am still new to Groovy and I don't know Grails. I don't want to throw away my Groovy codes and start over. What could be the fix of this problem? Many many thanks in advance!

Answer 1

I've never tried using JsonGroovyBuilder, so can't really help you with that. I was similar frustrated by the JSON Builder provided by Grails 1.1 (which was replaced with a better version in Grails 1.2). I overcame this frustration by writing my own Groovy JSON builder, which you're welcome to use. I've pasted the source code below.
import org.json.JSONStringer
/**
* An alternative JSON builder, because <code>grails.util.JSonBuilder</code> sucks!
* The reasons why it sucks are described here: http://www.anyware.co.uk/2005/2008/06/19/a-grails-json-builder-that-doesnt-suck/
* Although this page provides an alternative JSON builder, the author didn't provide any usage examples, and I couldn't
* figure out how to use it, so I wrote my own instead.
*
* The underlying JSON functionality is provided by <code>json.org.JSONStringer</code>. An example usage is:
*
* <code>
* builder.array(['feck', 'arse', 'girls']) {
* foo(bar:'1', baz: '2') {
* hobbies(sport: 'snooker', drink: 'guinness')
* emptyObj([:])
* emptyArray([])
* }
* }
* builder.json
* </code>
*
* This will print:
* <code>
* ["feck","arse","girls", {"bar":"1", "baz":"2", "hobbies": {"sport":"snooker", "drink":"guinness"}, "emptyObj": {},"emptyArray":[]}]
* </code>
*
* Verifiable usage examples are provided by the unit tests. A few points worth noting (the term 'element' is used below
* to mean 'either a JSON object or JSON array'):
*
* <ul>
* <li>The nesting of elements is indicated by the nesting of closures in the usual Groovy builder fashion</li>
* <li>The name of the method is used as the name of the key when nesting an element within an object</li>
* <li>The name of the method is irrelevant when nesting an element within an array, but it is recommended
* to use either the method name 'object' or 'array' for the sake of code readability</li>
* <li>The decision to create an array or object is determined by the type of the method parameter. A map will cause
* an object to be created, any other type will cause an array to be created</li>
* <li>To create an empty array or an array whose contents are determined only by nested closures, either call
* <code>builder.array()</code> or <code>builder.keyName([])</code>. The latter should be used when nesting the empty
* array within an object and control over the key name is required.</li>
* <li>To create an empty object or an object whose contents are determined only by nested closures, either call
* <code>builder.object()</code> or <code>builder.keyName([:])</code>. The latter should be used when nesting the empty
* object within another object and control over the key name is required.</li>
* </ul>
*/
class SimpleJSONBuilder extends BuilderSupport {
private jsonText = new JSONStringer()
/**
* Returns the JSON text created by this builder
*/
String getJson() {
jsonText.toString()
}
String toString() {
getJson()
}
protected void setParent(Object parent, Object child) {
// Method is abstract in parent class, but an empty implementation is all we need
}
/**
* Creates an array or object which is either empty, or whose contents are determined exclusively by nested closures.
*/
protected Object createNode(Object name) {
if (current == ElementType.OBJECT) {
throw new IllegalStateException("""Error processing method $name() Empty argument methods should not be invoked
when nesting an element within an object because the key name cannot be determined. Replace this call with either
$name([]) or $name([:])""")
}
if (name == 'array') {
jsonText.array()
return ElementType.ARRAY
} else if (name == 'object') {
jsonText.object()
return ElementType.OBJECT
} else {
throw new IllegalArgumentException("""When calling a method with no arguments, the method must be named either
'$array' or '$object' to indicate which you wish to create""")
}
}
protected Object createNode(Object name, Map attributes, Object value) {
throw new UnsupportedOperationException("Error invoking method $name. Method calls must supply either a single object (to create an array) or a Map (to create an object)")
}
/**
* Ensures that an array/object is correctly nested within an object
* #name Name of the key to use for the nested element
* #return The type of element
*/
private void nestElement(name) {
if (current == ElementType.OBJECT) {
jsonText.key(name)
}
}
/**
* Creates an array
* #name Name of the method. This will be used as the key if the array is nested within an object
* #value The contents of the array. This should be either a single value or a collection or array
* #return The type of element
*/
protected Object createNode(Object name, Object value) {
nestElement(name)
jsonText.array()
if (value instanceof Collection || value instanceof Object[]) {
value.each {jsonText.value(it)}
} else {
jsonText.value(value)
}
return ElementType.ARRAY
}
/**
* Creates an object
* #name Name of the method. This will be used as the key if the object is nested within an object
* #value The name-value pairs contained by this object
* #return The type of element
*/
protected Object createNode(Object name, Map attributes) {
nestElement(name)
jsonText.object()
attributes.each {key, value ->
jsonText.key(key).value(value)
}
return ElementType.OBJECT
}
protected void nodeCompleted(Object parent, Object node) {
node == ElementType.OBJECT ? jsonText.endObject() : jsonText.endArray()
}
}
private enum ElementType {
ARRAY, OBJECT
}
The source code above defines the class SimpleJSONBuilder and the enum SimpleJSONBuilder, but you can store both of these in a single file SimpleJSONBuilder.groovy.
The only library required by this builder is the Java JSON library provided by json.org.
In case the comments in the code above don't explain how to use it sufficiently well, here are some test cases:
public class SimpleJSONBuilderTests extends GroovyTestCase {
void testRootArrayElement() {
def builder = new SimpleJSONBuilder()
builder.array(['feck', 'arse', 'girls']) {
foo(bar: '1', baz: '2') {
hobbies(sport: 'snooker', drink: 'guinness')
emptyObj([:])
emptyArray([])
}
}
assertEquals builder.json, '["feck","arse","girls",{"bar":"1","baz":"2","hobbies":{"sport":"snooker","drink":"guinness"},"emptyObj":{},"emptyArray":[]}]'
}
void testRootObjElement() {
def builder = new SimpleJSONBuilder()
builder.object(feck:'arse') {
foo(bar: '1', baz: '2') {
hobbies(sport: 'snooker', drink: 'guinness')
emptyObj([:])
emptyArray([])
}
}
assertEquals builder.json, '{"feck":"arse","foo":{"bar":"1","baz":"2","hobbies":{"sport":"snooker","drink":"guinness"},"emptyObj":{},"emptyArray":[]}}'
}
/**
* Test that both mechanisms for creating empty arrays are equivalent
*/
void testEmptyArrays() {
def builder = new SimpleJSONBuilder()
builder.array([])
def builder2 = new SimpleJSONBuilder()
builder2.array()
assertEquals builder.json, builder2.json
assertEquals builder.json, "[]"
}
/**
* Test that both mechanisms for creating empty objects are equivalent
*/
void testEmptyObjects() {
def builder = new SimpleJSONBuilder()
builder.object([:])
def builder2 = new SimpleJSONBuilder()
builder2.object()
assertEquals builder.json, builder2.json
assertEquals builder.json, "{}"
}
}

Answer 2

It is a minor bug in JsonGroovyBuilder. If you use it from script, then unknown properties are resolved using script's binding.
I have posted a patch for JsonBuilder, so I hope the bug will be resolved soon.
See https://sourceforge.net/tracker/?func=detail&aid=3022114&group_id=171425&atid=857928 for details.