Bael 361 jackson streaming (#1459)

* BAEL-361 tests for Streaming API

* BAEL-361 do not use deprecated API

* BAEL-361 return to not read whole json document, only needed field

jackson/src/test/java/com/baeldung/jackson/streaming/JacksonStreamingAPITest.java

@@ -0,0 +1,119 @@
+package com.baeldung.jackson.streaming;
+
+
+import com.fasterxml.jackson.core.*;
+import org.junit.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+
+import static junit.framework.Assert.assertNull;
+import static junit.framework.Assert.assertTrue;
+import static junit.framework.TestCase.assertEquals;
+
+public class JacksonStreamingAPITest {
+
+    @Test
+    public void givenJsonGenerator_whenAppendJsonToIt_thenGenerateJson() throws IOException {
+        //given
+        ByteArrayOutputStream stream = new ByteArrayOutputStream();
+        JsonFactory jfactory = new JsonFactory();
+        JsonGenerator jGenerator = jfactory.createGenerator(stream, JsonEncoding.UTF8);
+
+        //when
+        jGenerator.writeStartObject();
+        jGenerator.writeStringField("name", "Tom");
+        jGenerator.writeNumberField("age", 25);
+        jGenerator.writeFieldName("address");
+        jGenerator.writeStartArray();
+        jGenerator.writeString("Poland");
+        jGenerator.writeString("5th avenue");
+        jGenerator.writeEndArray();
+        jGenerator.writeEndObject();
+        jGenerator.close();
+
+        //then
+        String json = new String(stream.toByteArray(), "UTF-8");
+        assertEquals(json, "{\"name\":\"Tom\",\"age\":25,\"address\":[\"Poland\",\"5th avenue\"]}");
+    }
+
+    @Test
+    public void givenJson_whenReadItUsingStreamAPI_thenShouldCreateProperJsonObject() throws IOException {
+        //given
+        String json = "{\"name\":\"Tom\",\"age\":25,\"address\":[\"Poland\",\"5th avenue\"]}";
+        JsonFactory jfactory = new JsonFactory();
+        JsonParser jParser = jfactory.createParser(json);
+
+        String parsedName = null;
+        Integer parsedAge = null;
+        List<String> addresses = new LinkedList<>();
+
+        //when
+        while (jParser.nextToken() != JsonToken.END_OBJECT) {
+
+            String fieldname = jParser.getCurrentName();
+            if ("name".equals(fieldname)) {
+                jParser.nextToken();
+                parsedName = jParser.getText();
+
+            }
+
+            if ("age".equals(fieldname)) {
+                jParser.nextToken();
+                parsedAge = jParser.getIntValue();
+
+            }
+
+            if ("address".equals(fieldname)) {
+                jParser.nextToken();
+
+                while (jParser.nextToken() != JsonToken.END_ARRAY) {
+                    addresses.add(jParser.getText());
+                }
+            }
+
+        }
+        jParser.close();
+
+        //then
+        assertEquals(parsedName, "Tom");
+        assertEquals(parsedAge, (Integer) 25);
+        assertEquals(addresses, Arrays.asList("Poland", "5th avenue"));
+
+    }
+
+    @Test
+    public void givenJson_whenWantToExtractPartOfIt_thenShouldExtractOnlyNeededFieldWithoutGoingThroughWholeJSON() throws IOException {
+        //given
+        String json = "{\"name\":\"Tom\",\"age\":25,\"address\":[\"Poland\",\"5th avenue\"]}";
+        JsonFactory jfactory = new JsonFactory();
+        JsonParser jParser = jfactory.createParser(json);
+
+        String parsedName = null;
+        Integer parsedAge = null;
+        List<String> addresses = new LinkedList<>();
+
+        //when
+        while (jParser.nextToken() != JsonToken.END_OBJECT) {
+
+            String fieldname = jParser.getCurrentName();
+
+            if ("age".equals(fieldname)) {
+                jParser.nextToken();
+                parsedAge = jParser.getIntValue();
+                return;
+            }
+
+        }
+        jParser.close();
+
+        //then
+        assertNull(parsedName);
+        assertEquals(parsedAge, (Integer) 25);
+        assertTrue(addresses.isEmpty());
+
+    }
+}