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928107
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2011-01-18T19:33:19.977
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2009-05-29T20:53:50.787
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2013-12-25T18:34:51.067
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<p>You are using Lift 1.0's <code>JsCmd</code>, which produces JSON with single-quoted strings and attempting to parse it with scala's parser, which only supports double-quoted strings.</p> <p>It is important to realize that there are multiple definitions for JSON.</p> <p>Are single-quoted strings valid in JSON?</p> <ul> <li>They are according to <a href="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf" rel="noreferrer">ECMAScript 5th Ed</a></li> <li>They are not according to Crockford's original <a href="http://www.ietf.org/rfc/rfc4627.txt" rel="noreferrer">RFC 4627</a></li> </ul> <p>Lift and Scala provide many ways to parse JSON, sometimes with differing behavior between versions.</p> <p>The strings accepted by these parsers are not equivalent.</p> <p>Here are some comments and examples of the various methods to product and parse JSON strings.</p> <hr> <h2>Producing JSON with the <a href="https://github.com/lift/lift/tree/master/framework/lift-base/lift-json/" rel="noreferrer">lift-json</a> library DSL</h2> <ul> <li>Recommended</li> <li>Despite its name, this is a separate project with no dependencies on the rest of Lift</li> </ul> <p>example:</p> <pre><code>scala> import net.liftweb.json.JsonAST import net.liftweb.json.JsonAST scala> import net.liftweb.json.JsonDSL._ import net.liftweb.json.JsonDSL._ scala> import net.liftweb.json.Printer._ import net.liftweb.json.Printer._ scala> val json1 = ("foo" -> 4) ~ ("bar" -> "baz") json1: net.liftweb.json.JsonAST.JObject = JObject(List(JField(foo,JInt(4)), JField(bar,JString(baz)))) scala> compact(JsonAST.render(json1)) res0: String = {"foo":4,"bar":"baz"} scala> val json2 = List(1,2,3) json2: List[Int] = List(1, 2, 3) scala> compact(JsonAST.render(json2)) res1: String = [1,2,3] scala> val json3 = ("foo", 4) ~ ("bar", List(1,2,3)) json3: net.liftweb.json.JsonAST.JObject = JObject(List(JField(foo,JInt(4)), JField(bar,JArray(List(JInt(1), JInt(2), JInt(3)))))) scala> compact(JsonAST.render(json3)) res2: String = {"foo":4,"bar":[1,2,3]} </code></pre> <hr> <h2>Parsing JSON with the <a href="https://github.com/lift/lift/tree/master/framework/lift-base/lift-json/" rel="noreferrer">lift-json</a> library</h2> <ul> <li>Recommended</li> <li>Provides implicit mapping to/from scala case-classes</li> <li>Case-classes defined in the console are not currently supported (will throw a <code>com.thoughtworks.paranamer.ParameterNamesNotFoundException: Unable to get class bytes</code>)</li> <li>The example below uses <code><a href="http://www.scala-lang.org/api/current/scala/xml/dtd/PublicID.html" rel="noreferrer">PublicID</a></code>, a pre-existing scala case-class so that it will work on the scala console.</li> </ul> <p>example:</p> <pre><code>scala> import scala.xml.dtd.PublicID import scala.xml.dtd.PublicID scala> import net.liftweb.json._ import net.liftweb.json._ scala> import net.liftweb.json.JsonAST._ import net.liftweb.json.JsonAST._ scala> import net.liftweb.json.JsonDSL._ import net.liftweb.json.JsonDSL._ scala> implicit val formats = DefaultFormats formats: net.liftweb.json.DefaultFormats.type = net.liftweb.json.DefaultFormats$@7fa27edd scala> val jsonAst = ("publicId1" -> "idString") ~ ("systemId" -> "systemIdStr") jsonAst: net.liftweb.json.JsonAST.JObject = JObject(List(JField(publicId,JString(idString)), JField(systemId,JString(systemIdStr)))) scala> jsonAst.extract[PublicID] res0: scala.xml.dtd.PublicID = PUBLIC "idString" "systemIdStr" </code></pre> <hr> <h2>Parsing JSON in scala 2.7.7 and 2.8.1</h2> <ul> <li>Not Recommended - "<a href="http://www.quora.com/How-do-I-parse-a-JSON-string-in-scala" rel="noreferrer">No longer really supported</a>"</li> <li>Scala 2.7.7's parser will not parse single-quoted JSON </li> <li>This parsing method used in the question</li> </ul> <p>example:</p> <pre><code>scala>import scala.util.parsing.json.JSON._ import scala.util.parsing.json.JSON._ scala> parseFull("{\"foo\" : 4 }") res1: Option[Any] = Some(Map(foo -> 4.0)) scala> parseFull("[ 1,2,3 ]") res2: Option[Any] = Some(List(1.0, 2.0, 3.0)) scala> parseFull("{'foo' : 4 }") res3: Option[Any] = None </code></pre> <hr> <h2>Parsing JSON in Lift 2.0 and 2.2 with <a href="http://main.scala-tools.org/mvnsites/liftweb-2.0/framework/scaladocs/net/liftweb/util/JSONParser$object.html" rel="noreferrer">util.JSONParser</a></h2> <ul> <li>Neutral Recommendation</li> <li>Lift's util.JSONParser will parse single- or double-quoted JSON strings:</li> </ul> <p>example:</p> <pre><code>scala> import net.liftweb.util.JSONParser._ import net.liftweb.util.JSONParser._ scala> parse("{\"foo\" : 4 }") res1: net.liftweb.common.Box[Any] = Full(Map(foo -> 4.0)) scala> parse("[ 1,2,3 ]") res2: net.liftweb.common.Box[Any] = Full(List(1.0, 2.0, 3.0)) scala> parse("{'foo' : 4}") res3: net.liftweb.common.Box[Any] = Full(Map(foo -> 4.0)) </code></pre> <hr> <h2>Parsing JSON in Lift 2.0 and 2.2 with <a href="http://main.scala-tools.org/mvnsites/liftweb-2.0/framework/scaladocs/net/liftweb/json/JsonParser$object.html" rel="noreferrer">json.JsonParser</a></h2> <ul> <li>Neutral Recommendation</li> <li>Lift's json.JsonParser will not parse single-quoted JSON strings:</li> </ul> <p>example:</p> <pre><code>scala> import net.liftweb.json._ import net.liftweb.json._ scala> import net.liftweb.json.JsonParser._ import net.liftweb.json.JsonParser._ scala> parse("{\"foo\" : 4 }") res1: net.liftweb.json.JsonAST.JValue = JObject(List(JField(foo,JInt(4)))) scala> parse("[ 1,2,3 ]") res2: net.liftweb.json.JsonAST.JValue = JArray(List(JInt(1), JInt(2), JInt(3))) scala> parse("{'foo' : 4}") net.liftweb.json.JsonParser$ParseException: unknown token ' Near: {'foo' : 4} at net.liftweb.json.JsonParser$Parser.fail(JsonParser.scala:216) at net.liftweb.json.JsonParser$Parser.nextToken(JsonParser.scala:308) at net.liftweb.json.JsonParser$$anonfun$1.apply(JsonParser.scala:172) at net.liftweb.json.JsonParser$$anonfun$1.apply(JsonParser.scala:129) at net.liftweb.json.JsonParse... </code></pre> <hr> <h2>Producing JSON with Lift 1.0 JsCmd</h2> <ul> <li>Not Recommended - output not valid for all JSON parsers</li> <li>Note the single-quotations around strings:</li> </ul> <p>example:</p> <pre><code>scala> import net.liftweb.http.js._ import net.liftweb.http.js._ scala> import net.liftweb.http.js.JE._ import net.liftweb.http.js.JE._ scala> JsObj(("foo", 4), ("bar", "baz")).toJsCmd res0: String = {'foo': 4, 'bar': 'baz'} scala> JsArray(1,2,3).toJsCmd res1: String = [1, 2, 3] scala> JsObj(("foo", 4), ("bar", JsArray(1,2,3))).toJsCmd res2: String = {'foo': 4, 'bar': [1, 2, 3] } </code></pre> <hr> <h2>Producing JSON with Lift 2.0 JsCmd</h2> <ul> <li>Neutral Recommendation</li> <li>Note the double quotations around strings:</li> </ul> <p>example:</p> <pre><code>scala> import net.liftweb.http.js._ import net.liftweb.http.js._ scala> import net.liftweb.http.js.JE._ import net.liftweb.http.js.JE._ scala> JsObj(("foo", 4), ("bar", "baz")).toJsCmd res0: String = {"foo": 4, "bar": "baz"} scala> JsArray(1,2,3).toJsCmd res1: String = [1, 2, 3] scala> JsObj(("foo", 4), ("bar", JsArray(1,2,3))).toJsCmd res3: String = {"foo": 4, "bar": [1, 2, 3] } </code></pre> <hr> <h2>Producint JSON in scala (tested with 2.10)</h2> <ul> <li>"<a href="http://www.quora.com/How-do-I-parse-a-JSON-string-in-scala" rel="noreferrer">No longer really supported</a>", but it works and it's there.</li> </ul> <p>example:</p> <pre><code>scala> import scala.util.parsing.json._ import scala.util.parsing.json._ scala> JSONObject (Map ("foo" -> 4, "bar" -> JSONArray (1 :: 2 :: 3 :: Nil))) .toString() res0: String = {"foo" : 4, "bar" : [1, 2, 3]} </code></pre>
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