BAEL-2922 Add Json to CSV code using Jackson CsvMapper (#7115)

jackson-2/pom.xml

@@ -28,6 +28,13 @@
             <artifactId>jackson-dataformat-yaml</artifactId>
             <version>2.9.8</version>
         </dependency>
+        
+        <!-- CSV -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.dataformat</groupId>
+            <artifactId>jackson-dataformat-csv</artifactId>
+            <version>2.9.8</version>
+        </dependency>        
 
         <!-- Allow use of LocalDate -->
         <dependency>

jackson-2/src/main/java/com/baeldung/jackson/csv/JsonCsvConverter.java

@@ -0,0 +1,59 @@
+package com.baeldung.jackson.csv;
+
+import java.io.File;
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.OrderLine;
+import com.baeldung.jackson.mixin.OrderLineForCsv;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.MappingIterator;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.dataformat.csv.CsvMapper;
+import com.fasterxml.jackson.dataformat.csv.CsvSchema;
+import com.fasterxml.jackson.dataformat.csv.CsvSchema.Builder;
+
+public class JsonCsvConverter {
+    
+    public static void JsonToCsv(File jsonFile, File csvFile) throws IOException {
+        JsonNode jsonTree = new ObjectMapper().readTree(jsonFile);
+        
+        Builder csvSchemaBuilder = CsvSchema.builder();
+        JsonNode firstObject = jsonTree.elements().next();
+        firstObject.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
+        CsvSchema csvSchema = csvSchemaBuilder
+            .build()
+            .withHeader();
+        
+        CsvMapper csvMapper = new CsvMapper();
+        csvMapper.writerFor(JsonNode.class)
+            .with(csvSchema)
+            .writeValue(csvFile, jsonTree);
+    }
+    
+    public static void csvToJson(File csvFile, File jsonFile) throws IOException {
+        CsvSchema orderLineSchema = CsvSchema.emptySchema().withHeader();
+        CsvMapper csvMapper = new CsvMapper();
+        MappingIterator<OrderLine> orderLines = csvMapper.readerFor(OrderLine.class)
+            .with(orderLineSchema)
+            .readValues(csvFile);
+        
+        new ObjectMapper()
+            .configure(SerializationFeature.INDENT_OUTPUT, true)
+            .writeValue(jsonFile, orderLines.readAll());
+    }
+
+    public static void JsonToFormattedCsv(File jsonFile, File csvFile) throws IOException {
+        CsvMapper csvMapper = new CsvMapper();
+        CsvSchema csvSchema = csvMapper
+            .schemaFor(OrderLineForCsv.class)
+            .withHeader();
+        csvMapper.addMixIn(OrderLine.class, OrderLineForCsv.class);
+        
+        OrderLine[] orderLines = new ObjectMapper()
+            .readValue(jsonFile, OrderLine[].class);
+        csvMapper.writerFor(OrderLine[].class)
+            .with(csvSchema)
+            .writeValue(csvFile, orderLines);
+    }
+}

jackson-2/src/main/java/com/baeldung/jackson/mixin/OrderLineForCsv.java

@@ -0,0 +1,25 @@
+package com.baeldung.jackson.mixin;
+
+import java.math.BigDecimal;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
+
+@JsonPropertyOrder({
+    "count",
+    "name"
+})
+public abstract class OrderLineForCsv {
+    
+    @JsonProperty("name")
+    private String item; 
+    
+    @JsonProperty("count")
+    private int quantity; 
+    
+    @JsonIgnore
+    private BigDecimal unitPrice;
+    
+
+}

jackson-2/src/main/resources/orderLines.csv

@@ -0,0 +1,3 @@
+item,quantity,unitPrice
+"No. 9 Sprockets",12,1.23
+"Widget (10mm)",4,3.45

jackson-2/src/main/resources/orderLines.json

@@ -0,0 +1,9 @@
+[ {
+  "item" : "No. 9 Sprockets",
+  "quantity" : 12,
+  "unitPrice" : 1.23
+}, {
+  "item" : "Widget (10mm)",
+  "quantity" : 4,
+  "unitPrice" : 3.45
+} ]

jackson-2/src/test/java/com/baeldung/jackson/csv/CsvUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.jackson.csv;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.util.List;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.core.JsonParseException;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.google.common.io.Files;
+
+
+public class CsvUnitTest {
+
+    @Test
+    public void givenJsonInput_thenWriteCsv() throws JsonParseException, JsonMappingException, IOException {
+        JsonCsvConverter.JsonToCsv(new File("src/main/resources/orderLines.json"), 
+            new File("src/main/resources/csvFromJson.csv"));
+        
+        assertEquals(readFile("src/main/resources/csvFromJson.csv"),
+            readFile("src/test/resources/expectedCsvFromJson.csv"));
+    }
+    
+    @Test
+    public void givenCsvInput_thenWritesJson() throws JsonParseException, JsonMappingException, IOException {
+        JsonCsvConverter.csvToJson(new File("src/main/resources/orderLines.csv"), 
+            new File("src/main/resources/jsonFromCsv.json"));
+        
+        assertEquals(readFile("src/main/resources/jsonFromCsv.json"),
+            readFile("src/test/resources/expectedJsonFromCsv.json"));
+        
+    }
+    
+    @Test
+    public void givenJsonInput_thenWriteFormattedCsvOutput() throws JsonParseException, JsonMappingException, IOException {
+        JsonCsvConverter.JsonToFormattedCsv(new File("src/main/resources/orderLines.json"), 
+            new File("src/main/resources/formattedCsvFromJson.csv"));
+
+        assertEquals(readFile("src/main/resources/formattedCsvFromJson.csv"),
+            readFile("src/test/resources/expectedFormattedCsvFromJson.csv"));
+        
+    }
+    
+    private List<String> readFile(String filename) throws IOException {
+        return Files.readLines(new File(filename), Charset.forName("utf-8"));
+    }
+    
+    
+}
+;

jackson-2/src/test/resources/expectedCsvFromJson.csv

@@ -0,0 +1,3 @@
+item,quantity,unitPrice
+"No. 9 Sprockets",12,1.23
+"Widget (10mm)",4,3.45

jackson-2/src/test/resources/expectedFormattedCsvFromJson.csv

@@ -0,0 +1,3 @@
+count,name
+12,"No. 9 Sprockets"
+4,"Widget (10mm)"

jackson-2/src/test/resources/expectedJsonFromCsv.json

@@ -0,0 +1,9 @@
+[ {
+  "item" : "No. 9 Sprockets",
+  "quantity" : 12,
+  "unitPrice" : 1.23
+}, {
+  "item" : "Widget (10mm)",
+  "quantity" : 4,
+  "unitPrice" : 3.45
+} ]