asmhatre
c438afc33b
37 runnable examples covering the eight feature posts on ankurm.com, verified against Jackson 3.2.1 on Temurin 21.0.5. Every output committed under docs/ was produced by run-all.sh. Also documents 11 places where the published snippets do not compile or do not behave as printed against a real Jackson 3 build - most notably that writeValueAsString(List<Base>) silently drops the polymorphic type discriminator, so the post's serialised output cannot be read back.
46 lines
1.8 KiB
Java
46 lines
1.8 KiB
Java
package com.ankurm.jackson3.part0setup;
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import tools.jackson.core.JsonParser;
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import tools.jackson.core.JsonToken;
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import tools.jackson.databind.JsonNode;
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import tools.jackson.databind.json.JsonMapper;
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/**
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* Post: Jackson 101 — https://ankurm.com/jackson-java-tutorial/
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* Section: "Jackson's Three Processing Models"
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*
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* The same payload read three ways, so the trade-off is concrete rather than a table.
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*/
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public class A03ThreeProcessingModels {
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public record Order(Long orderId, String status) { }
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private static final String JSON = "{\"orderId\":1001,\"status\":\"SHIPPED\"}";
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public static void main(String[] args) {
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JsonMapper mapper = JsonMapper.builder().build();
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// 1. DATA BINDING — the right answer roughly 95% of the time.
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Order bound = mapper.readValue(JSON, Order.class);
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System.out.println("1. data binding : " + bound);
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// 2. TREE MODEL — schema not known at compile time; navigate a JsonNode.
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JsonNode tree = mapper.readTree(JSON);
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System.out.println("2. tree model : orderId=" + tree.path("orderId").asInt()
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+ " status=" + tree.path("status").asString());
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// 3. STREAMING — token by token, constant memory, no document ever built.
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StringBuilder streamed = new StringBuilder();
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try (JsonParser parser = mapper.createParser(JSON)) {
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while (parser.nextToken() != null) {
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if (parser.currentToken() == JsonToken.PROPERTY_NAME) {
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String field = parser.currentName();
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parser.nextToken(); // advance to the value
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streamed.append(field).append('=').append(parser.getString()).append(' ');
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}
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}
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}
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System.out.println("3. streaming : " + streamed.toString().trim());
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}
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}
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