Add source code for article BAEL-2463 (#7543)

jackson-2/src/main/java/com/baeldung/jackson/entities/File.java

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+package com.baeldung.jackson.entities;
+
+public class File {
+
+    private Long id;
+
+    private String name;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/entities/Folder.java

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+package com.baeldung.jackson.entities;
+
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.List;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+
+public class Folder {
+
+    private Long id;
+
+    private String name;
+
+    private String owner;
+
+    private Date created;
+
+    private Date modified;
+
+    private Date lastAccess;
+
+    @JsonIgnore
+    private List<File> files = new ArrayList<>();
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getOwner() {
+        return owner;
+    }
+
+    public void setOwner(String owner) {
+        this.owner = owner;
+    }
+
+    public Date getCreated() {
+        return created;
+    }
+
+    public void setCreated(Date created) {
+        this.created = created;
+    }
+
+    public Date getModified() {
+        return modified;
+    }
+
+    public void setModified(Date modified) {
+        this.modified = modified;
+    }
+
+    public Date getLastAccess() {
+        return lastAccess;
+    }
+
+    public void setLastAccess(Date lastAccess) {
+        this.lastAccess = lastAccess;
+    }
+
+    public List<File> getFiles() {
+        return files;
+    }
+
+    public void setFiles(List<File> files) {
+        this.files = files;
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderBeanSerializerModifier.java

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+package com.baeldung.jackson.serialization.custom.serializer;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.databind.BeanDescription;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializationConfig;
+import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
+
+public class FolderBeanSerializerModifier extends BeanSerializerModifier {
+
+    @Override
+    public JsonSerializer<?> modifySerializer(SerializationConfig config, BeanDescription beanDesc, JsonSerializer<?> serializer) {
+
+        if (beanDesc.getBeanClass().equals(Folder.class)) {
+            return new FolderSerializerWithDefaultSerializerStored((JsonSerializer<Object>) serializer);
+        }
+
+        return serializer;
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializer.java

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+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.File;
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializer extends StdSerializer<Folder> {
+
+    public FolderSerializer() {
+        super(Folder.class);
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        gen.writeArrayFieldStart("files");
+        for (File file : value.getFiles()) {
+            gen.writeStartObject();
+            gen.writeNumberField("id", file.getId());
+            gen.writeStringField("name", file.getName());
+            gen.writeEndObject();
+        }
+        gen.writeEndArray();
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializerWithCallingOwnSerializer.java

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+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializerWithCallingOwnSerializer extends StdSerializer<Folder> {
+
+    public FolderSerializerWithCallingOwnSerializer() {
+        super(Folder.class);
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        provider.defaultSerializeField("files", value.getFiles(), gen);
+
+        provider.defaultSerializeField("details", value, gen);
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializerWithDefaultSerializerStored.java

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+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializerWithDefaultSerializerStored extends StdSerializer<Folder> {
+
+    private final JsonSerializer<Object> defaultSerializer;
+
+    public FolderSerializerWithDefaultSerializerStored(JsonSerializer<Object> defaultSerializer) {
+        super(Folder.class);
+        this.defaultSerializer = defaultSerializer;
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        provider.defaultSerializeField("files", value.getFiles(), gen);
+
+        gen.writeFieldName("details");
+        defaultSerializer.serialize(value, gen, provider);
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializerWithInternalObjectMapper.java

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+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializerWithInternalObjectMapper extends StdSerializer<Folder> {
+
+    public FolderSerializerWithInternalObjectMapper() {
+        super(Folder.class);
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        // we access internal mapper to delegate the serialization of File list  
+        ObjectMapper mapper = (ObjectMapper) gen.getCodec();
+
+        gen.writeFieldName("files");
+        String stringValue = mapper.writeValueAsString(value.getFiles());
+        gen.writeRawValue(stringValue);
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializerWithSerializerProvider.java

@@ -0,0 +1,29 @@
+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializerWithSerializerProvider extends StdSerializer<Folder> {
+
+    public FolderSerializerWithSerializerProvider() {
+        super(Folder.class);
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        // we delegate the File list serialization to its default serializer
+        provider.defaultSerializeField("files", value.getFiles(), gen);
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/test/java/com/baeldung/jackson/serialization/custom/serializer/CallingDefaultSerializerUnitTest.java

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+package com.baeldung.jackson.serialization.custom.serializer;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import com.baeldung.jackson.entities.File;
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+
+public class CallingDefaultSerializerUnitTest {
+
+    private ObjectMapper mapper;
+    private Folder mockFolder;
+    private TypeReference<HashMap<String, Object>> mapType;
+
+    @Before
+    public void setup() {
+
+        mapType = new TypeReference<HashMap<String, Object>>() {
+        };
+
+        mapper = new ObjectMapper();
+
+        mockFolder = new Folder();
+        mockFolder.setId(1L);
+        mockFolder.setName("Root Folder");
+        mockFolder.setOwner("root");
+        mockFolder.setCreated(Date.from(Instant.now().minusSeconds(60)));
+        mockFolder.setModified(Date.from(Instant.now().minusSeconds(30)));
+        mockFolder.setLastAccess(Date.from(Instant.now()));
+
+        File file1 = new File();
+        file1.setId(1L);
+        file1.setName("File 1");
+
+        File file2 = new File();
+        file2.setId(2L);
+        file2.setName("File 2");
+
+        List<File> files = new ArrayList<>();
+        files.add(file1);
+        files.add(file2);
+        mockFolder.setFiles(files);
+
+    }
+
+    @Test
+    public void givenFolder_whenSerialized_onlyNameAndFilesFieldsSerialized() throws IOException {
+
+        SimpleModule module = new SimpleModule();
+        module.addSerializer(new FolderSerializer());
+        mapper.registerModule(module);
+
+        String json = mapper.writeValueAsString(mockFolder);
+
+        HashMap<String, Object> actual = mapper.readValue(json, mapType);
+
+        assertTrue(actual.containsKey("name"));
+        assertTrue(actual.containsKey("files"));
+        assertEquals(mockFolder.getName(), actual.get("name"));
+
+        List actualFiles = (List) actual.get("files");
+        assertEquals(mockFolder.getFiles().size(), actualFiles.size());
+        
+    }
+
+    @Test
+    public void givenFolder_whenSerializedWithSerializerProvider_onlyNameAndFilesFieldsSerialized() throws IOException {
+
+        SimpleModule module = new SimpleModule();
+        module.addSerializer(new FolderSerializerWithSerializerProvider());
+        mapper.registerModule(module);
+
+        String json = mapper.writeValueAsString(mockFolder);
+
+        HashMap<String, Object> actual = mapper.readValue(json, mapType);
+
+        assertTrue(actual.containsKey("name"));
+        assertTrue(actual.containsKey("files"));
+        assertEquals(mockFolder.getName(), actual.get("name"));
+
+        List actualFiles = (List) actual.get("files");
+        assertEquals(mockFolder.getFiles().size(), actualFiles.size());
+
+    }
+
+    @Test
+    public void givenFolder_whenSerializedWithInternalObjectMapper_onlyNameAndFilesFieldsSerialized() throws IOException {
+
+        SimpleModule module = new SimpleModule();
+        module.addSerializer(new FolderSerializerWithInternalObjectMapper());
+        mapper.registerModule(module);
+
+        String json = mapper.writeValueAsString(mockFolder);
+
+        HashMap<String, Object> actual = mapper.readValue(json, mapType);
+
+        assertTrue(actual.containsKey("name"));
+        assertTrue(actual.containsKey("files"));
+        assertEquals(mockFolder.getName(), actual.get("name"));
+
+        List actualFiles = (List) actual.get("files");
+        assertEquals(mockFolder.getFiles().size(), actualFiles.size());
+
+    }
+
+    @Test(expected = StackOverflowError.class)
+    public void givenFolder_whenSerializedWithCallingOwnSerializer_exceptionOccured() throws IOException {
+
+        SimpleModule module = new SimpleModule();
+        module.addSerializer(new FolderSerializerWithCallingOwnSerializer());
+        mapper.registerModule(module);
+
+        mapper.writeValueAsString(mockFolder);
+        
+    }
+
+    @Test
+    public void givenFolder_whenSerializedWithDefaultSerializerStored_NameAndFilesAndDetailsFieldsSerialized() throws IOException {
+
+        SimpleModule module = new SimpleModule();
+        module.setSerializerModifier(new FolderBeanSerializerModifier());
+        mapper.registerModule(module);
+
+        String json = mapper.writeValueAsString(mockFolder);
+        
+        HashMap<String, Object> actual = mapper.readValue(json, mapType);
+
+        assertTrue(actual.containsKey("name"));
+        assertTrue(actual.containsKey("files"));
+        assertEquals(mockFolder.getName(), actual.get("name"));
+
+        List actualFiles = (List) actual.get("files");
+        assertEquals(mockFolder.getFiles().size(), actualFiles.size());
+        
+        Map actualDetails = (Map) actual.get("details");
+        assertTrue(actualDetails.containsKey("id"));
+        assertTrue(actualDetails.containsKey("name"));
+        assertTrue(actualDetails.containsKey("owner"));
+        assertTrue(actualDetails.containsKey("created"));
+        assertTrue(actualDetails.containsKey("modified"));
+        assertTrue(actualDetails.containsKey("lastAccess"));
+        
+        assertEquals(mockFolder.getId().longValue(), ((Number)actualDetails.get("id")).longValue());
+        assertEquals(mockFolder.getName(), actualDetails.get("name"));
+        assertEquals(mockFolder.getOwner(), actualDetails.get("owner"));
+        assertEquals(mockFolder.getCreated(), new Date((long) actualDetails.get("created")));
+        assertEquals(mockFolder.getModified(), new Date((long) actualDetails.get("modified")));
+        assertEquals(mockFolder.getLastAccess(), new Date((long) actualDetails.get("lastAccess")));
+
+    }
+
+}