{"id":15413,"date":"2022-10-11T12:41:42","date_gmt":"2022-10-11T07:11:42","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-parsing-large-json-with-java-gson-cant-read-the-json-structure\/"},"modified":"2022-10-11T12:41:42","modified_gmt":"2022-10-11T07:11:42","slug":"solved-parsing-large-json-with-java-gson-cant-read-the-json-structure","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-parsing-large-json-with-java-gson-cant-read-the-json-structure\/","title":{"rendered":"[Solved] parsing large JSON with java\/GSON, can&#8217;t read the JSON structure"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-69282822\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"69282822\" data-parentid=\"69275727\" data-score=\"2\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>JSON by default declares one top value only (and yes, this would be a <em>valid JSON document<\/em>), but there is <em>JSON streaming<\/em> that uses arbitrary techniques to concatenate multiple JSON elements into a single stream assuming that the stream consumer can parse it (<a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/en.wikipedia.org\/wiki\/JSON_streaming\">read more<\/a>). Gson supports a so-called lenient mode that turns off the &#8220;one top value only&#8221; mode (and does some more things irrelevant to the question) for <code>JsonReader<\/code>: <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.javadoc.io\/doc\/com.google.code.gson\/gson\/2.8.5\/com\/google\/gson\/stream\/JsonReader.html#setLenient-boolean-\"><code>setLenient<\/code><\/a>. Having the lenient mode on, you can read JSON elements one by one, and it turns out that this mode can be used to parse\/read <em>line-delimited JSON<\/em> and <em>concatenated JSON values<\/em> since they are simply delimited by zero or more whitespaces that are ignored by Gson (therefore more exotic <em>record separator-delimited JSON<\/em> and <em>length-prefixed JSON<\/em> are unsupported). The reason of why it does not work for you is that your initial code assumes that the stream contains a single JSON array (and it does not obviously: it is supposed to be a stream of elements that does not conform the JSON array syntax).<\/p>\n<p>A simple generic JSON stream support might look like this (using Stream API for its more rich API than <code>Iterator<\/code> has, but it is fine to show an idea, and you can easily adapt it to iterators, callbacks, observable streams, whatever you like):<\/p>\n<pre class=\"lang-java prettyprint-override\"><code>@UtilityClass\npublic final class JsonStreamSupport {\n\n    public static &lt;T&gt; Stream&lt;T&gt; parse(@WillNotClose final JsonReader jsonReader, final Function&lt;? super JsonReader, ? extends T&gt; readElement) {\n        final boolean isLenient = jsonReader.isLenient();\n        jsonReader.setLenient(true);\n        final Spliterator&lt;T&gt; spliterator = new Spliterators.AbstractSpliterator&lt;T&gt;(Long.MAX_VALUE, Spliterator.ORDERED) {\n            @Override\n            public boolean tryAdvance(final Consumer&lt;? super T&gt; action) {\n                try {\n                    final JsonToken token = jsonReader.peek();\n                    if ( token == JsonToken.END_DOCUMENT ) {\n                        return false;\n                    }\n                    \/\/ TODO: read more elements in batch\n                    final T element = readElement.apply(jsonReader);\n                    action.accept(element);\n                    return true;\n                } catch ( final IOException ex ) {\n                    throw new RuntimeException(ex);\n                }\n            }\n        };\n        return StreamSupport.stream(spliterator, false)\n                .onClose(() -&gt; jsonReader.setLenient(isLenient));\n    }\n\n}\n<\/code><\/pre>\n<p>And then:<\/p>\n<pre class=\"lang-java prettyprint-override\"><code>JsonStreamSupport.&lt;Artist&gt;parse(jsonReader, jr -&gt; gson.fromJson(jr, Artist.class))\n        .forEach(System.out::println);\n<\/code><\/pre>\n<p>Output (assuming <code>Artist<\/code> has Lombok-generated <code>toString()<\/code>):<\/p>\n<blockquote>\n<p>Artist(id=d0ab06e1-751a-414b-a976-da72670391b1, name=Arcing Wires, sortName=Arcing Wires)<br \/>\nArtist(id=6f0c2c16-dd7e-4268-a484-bc7b2ac78108, name=Another, sortName=Another)<br \/>\nArtist(id=e062b6cd-5506-47b0-afdb-72f4279ec38c, name=Agent S, sortName=Agent S)<\/p>\n<\/blockquote>\n<p>How many bytes does such an approach, JSON streaming, save so that it is used at the service you&#8217;re trying to consume? I don&#8217;t know.<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\"><\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved parsing large JSON with java\/GSON, can&#8217;t read the JSON structure <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] JSON by default declares one top value only (and yes, this would be a valid JSON document), but there is JSON streaming that uses arbitrary techniques to concatenate multiple JSON elements into a single stream assuming that the stream consumer can parse it (read more). Gson supports a so-called lenient mode that turns off &#8230; <a title=\"[Solved] parsing large JSON with java\/GSON, can&#8217;t read the JSON structure\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-parsing-large-json-with-java-gson-cant-read-the-json-structure\/\" aria-label=\"More on [Solved] parsing large JSON with java\/GSON, can&#8217;t read the JSON structure\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[1647,323,356],"class_list":["post-15413","post","type-post","status-publish","format-standard","hentry","category-solved","tag-gson","tag-java","tag-json"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] parsing large JSON with java\/GSON, can&#039;t read the JSON structure - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-parsing-large-json-with-java-gson-cant-read-the-json-structure\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] parsing large JSON with java\/GSON, can&#039;t read the JSON structure - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] JSON by default declares one top value only (and yes, this would be a valid JSON document), but there is JSON streaming that uses arbitrary techniques to concatenate multiple JSON elements into a single stream assuming that the stream consumer can parse it (read more). 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