Category: jackson

Jackson – ObjectMapper Class ”; Previous Next Introduction ObjectMapper is the main actor class of Jackson library. ObjectMapper class ObjectMapper provides functionality for reading and writing JSON, either to and from basic POJOs (Plain Old Java Objects), or to and from a general-purpose JSON Tree Model (JsonNode), as well as related functionality for performing conversions. It is also highly customizable to work both with different styles of JSON content, and to support more advanced Object concepts such as polymorphism and Object identity. ObjectMapper also acts as a factory for more advanced ObjectReader and ObjectWriter classes. Class Declaration Following is the declaration for com.fasterxml.jackson.databind.ObjectMapper class − public class ObjectMapper extends ObjectCodec implements Versioned, Serializable Nested Classes S.No. Class & Description 1 static class ObjectMapper.DefaultTypeResolverBuilder Customized TypeResolverBuilder that provides type resolver builders used with so-called “default typing” (see enableDefaultTyping() for details). 2 static class ObjectMapper.DefaultTyping Enumeration used with enableDefaultTyping() to specify what kind of types (classes) default typing should be used for. Fields protected DeserializationConfig _deserializationConfig – Configuration object that defines basic global settings for the serialization process. protected DefaultDeserializationContext _deserializationContext – Blueprint context object; stored here to allow custom sub-classes. protected InjectableValues _injectableValues – Provider for values to inject in deserialized POJOs. protected JsonFactory _jsonFactory – Factory used to create JsonParser and JsonGenerator instances as necessary. protected SimpleMixInResolver _mixIns – Mapping that defines how to apply mix-in annotations: key is the type to received additional annotations, and value is the type that has annotations to “mix in”. protected ConfigOverrides _propertyOverrides – Currently active per-type configuration overrides, accessed by declared type of property. protected Set<Object> _registeredModuleTypes – Set of module types (as per Module.getTypeId() that have been registered; kept track of iff MapperFeature.IGNORE_DUPLICATE_MODULE_REGISTRATIONS is enabled, so that duplicate registration calls can be ignored (to avoid adding same handlers multiple times, mostly). protected ConcurrentHashMap<JavaType,JsonDeserializer<Object>> _rootDeserializers – We will use a separate main-level Map for keeping track of root-level deserializers. protected SerializationConfig _serializationConfig – Configuration object that defines basic global settings for the serialization process. protected SerializerFactory _serializerFactory – Serializer factory used for constructing serializers. protected DefaultSerializerProvider _serializerProvider – Object that manages access to serializers used for serialization, including caching. protected SubtypeResolver _subtypeResolver – Thing used for registering sub-types, resolving them to super/sub-types as needed. protected TypeFactory _typeFactory – Specific factory used for creating JavaType instances; needed to allow modules to add more custom type handling (mostly to support types of non-Java JVM languages). protected static AnnotationIntrospector DEFAULT_ANNOTATION_INTROSPECTOR protected static BaseSettings DEFAULT_BASE – Base settings contain defaults used for all ObjectMapper instances. protected static VisibilityChecker<?> STD_VISIBILITY_CHECKER Constructors S.No. Constructor & Description 1 ObjectMapper() Default constructor, which will construct the default JsonFactory as necessary, use SerializerProvider as its SerializerProvider, and BeanSerializerFactory as its SerializerFactory. 2 ObjectMapper(JsonFactory jf) Constructs instance that uses specified JsonFactory for constructing necessary JsonParsers and/or JsonGenerators. 3 ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp) Constructs instance that uses specified JsonFactory for constructing necessary JsonParsers and/or JsonGenerators, and uses given providers for accessing serializers and deserializers. 4 protected ObjectMapper(ObjectMapper src) Copy-constructor, mostly used to support copy(). Methods 1 protected void _checkInvalidCopy(Class<?> exp) 2 protected void _configAndWriteValue(JsonGenerator g, Object value) – Method called to configure the generator as necessary and then call write functionality 3 protected Object _convert(Object fromValue, JavaType toValueType) – Actual conversion implementation: instead of using existing read and write methods, much of code is inlined. 4 protected JsonDeserializer<Object> _findRootDeserializer(DeserializationContext ctxt, JavaType valueType) – Method called to locate deserializer for the passed root-level value. 5 protected JsonToken _initForReading(JsonParser p) – Method called to ensure that given parser is ready for reading content for data binding. 6 protected ObjectReader _newReader(DeserializationConfig config) – Factory method sub-classes must override, to produce ObjectReader instances of proper sub-type 7 protected ObjectReader _newReader(DeserializationConfig config, JavaType valueType, Object valueToUpdate, FormatSchema schema, InjectableValues injectableValues) – Factory method sub-classes must override, to produce ObjectReader instances of proper sub-type 8 protected ObjectWriter _newWriter(SerializationConfig config) – Factory method sub-classes must override, to produce ObjectWriter instances of proper sub-type 9 protected ObjectWriter _newWriter(SerializationConfig config, FormatSchema schema) – Factory method sub-classes must override, to produce ObjectWriter instances of proper sub-type 10 protected ObjectWriter _newWriter(SerializationConfig config, JavaType rootType, PrettyPrinter pp) – Factory method sub-classes must override, to produce ObjectWriter instances of proper sub-type. 11 protected Object _readMapAndClose(JsonParser p0, JavaType valueType) 12 protected Object _readValue(DeserializationConfig cfg, JsonParser p, JavaType valueType) – Actual implementation of value reading+binding operation. 13 protected DefaultSerializerProvider _serializerProvider(SerializationConfig config) Overridable helper method used for constructing SerializerProvider to use for serialization. 14 protected Object _unwrapAndDeserialize(JsonParser p, DeserializationContext ctxt, DeserializationConfig config, JavaType rootType, JsonDeserializer<Object> deser) 15 protected void _verifySchemaType(FormatSchema schema) 16 void acceptJsonFormatVisitor(Class<?> type, JsonFormatVisitorWrapper visitor) – Method for visiting type hierarchy for given type, using specified visitor. 17 void acceptJsonFormatVisitor(JavaType type, JsonFormatVisitorWrapper visitor) – Method for visiting type hierarchy for given type, using specified visitor. 18 ObjectMapper addHandler(DeserializationProblemHandler h) – Method for adding specified DeserializationProblemHandler to be used for handling specific problems during deserialization. 19 ObjectMapper addMixIn(Class<?> target, Class<?> mixinSource) – Method to use for adding mix-in annotations to use for augmenting specified class or interface. void addMixInAnnotations(Class<?> target, Class<?> mixinSource) – Deprecated. Since 2.5: replaced by a fluent form of the method; addMixIn(Class, Class). 20 boolean canDeserialize(JavaType type) – Method that can be called to check whether mapper thinks it could deserialize an Object of given type. 21 boolean canDeserialize(JavaType type, AtomicReference<Throwable> cause) – Method similar to canDeserialize(JavaType) but that can return actual Throwable that was thrown when trying to construct serializer: this may be useful in figuring out what the actual problem is. 22 boolean canSerialize(Class<?> type) – Method that can be called to check whether mapper thinks it could serialize an instance of given Class. 23 boolean canSerialize(Class<?> type, AtomicReference<Throwable> cause) – Method similar to canSerialize(Class) but that can return actual Throwable that was thrown when trying to construct serializer: this may be useful in figuring out what the actual problem is. 24 ObjectMapper clearProblemHandlers() – Method for removing all registered DeserializationProblemHandlers instances from this mapper. 25 MutableConfigOverride configOverride(Classlt;?> type) – Accessor for getting a mutable configuration override object

Jackson – Useful Resources ”; Previous Next The following resources contain additional information on Jackson JSON Processor library. Please use them to get more in-depth knowledge on this topic. Useful Links on Jackson Jackson JSON Processor Wiki – Jackson JSON Processor Wiki page Jackson Project Home – Jackson JSON Processor Portal Page on GitHub. Books on Jackson To enlist your site on this page, please drop an email to [email protected] Print Page Previous Next Advertisements ”;

Jackson Tutorial PDF Version Quick Guide Resources Job Search Discussion Jackson is a very popular and efficient java based library to serialize or map java objects to JSON and vice versa. This tutorial will teach you basic and advanced Jackson library API features and their usage in a simple and intuitive way. Audience This reference has been prepared for the Java developers from beginner to expert level. After completing this tutorial you will find yourself at a moderate level of expertise in knowledge of Jackson library from where you can take yourself to next levels Prerequisites Jackson is a Java-based library and it is imperative that you should have a thorough knowledge of Java programming language before proceeding with this tutorial. Print Page Previous Next Advertisements ”;

Jackson – Overview ”; Previous Next Jackson is a simple java based library to serialize java objects to JSON and vice versa. Features Easy to use. – jackson API provides a high level facade to simplify commonly used use cases. No need to create mapping. – jackson API provides default mapping for most of the objects to be serialized. Performance. – jackson is quiet fast and is of low memory footprint and is suitable for large object graphs or systems. Clean JSON. – jackson creates a clean and compact JSON results which is easy to read. No Dependency. – jackson library does not require any other library apart from jdk. Open Source – jackson library is open source and is free to use. Three ways of processing JSON Jackson provides three alternative ways to process JSON Streaming API – reads and writes JSON content as discrete events. JsonParser reads the data whereas JsonGenerator writes the data. It is most powerful approach among the three and is of lowest overhead and fastest in read/write opreations. It is Analogus to Stax parser for XML. Tree Model – prepares a in-memory tree representation of the JSON document. ObjectMapper build tree of JsonNode nodes. It is most flexible approach. It is analogus to DOM parser for XML. Data Binding – converts JSON to and from POJO (Plain Old Java Object) using property accessor or using annotations. It is of two type. Simple Data Binding – Converts JSON to and from Java Maps, Lists, Strings, Numbers, Booleans and null objects. Full Data Binding – Converts JSON to and from any JAVA type. ObjectMapper reads/writes JSON for both types of data bindings. Data Binding is most convenient way and is analogus to JAXB parer for XML. Print Page Previous Next Advertisements ”;

Jackson – Streaming API ”; Previous Next Streaming API reads and writes JSON content as discrete events. JsonParser reads the data whereas JsonGenerator writes the data. It is most powerful approach among the three and is of lowest overhead and fastest in read/write opreations. It is Analogus to Stax parser for XML. In this Article, we”ll showcase using Jackson streaming APIs to read and write JSON data. Streaming API works with concept of token and every details of Json is to be handle carefuly. Following are two class which we”ll use in the examples: JsonGenerator – Write to JSON String. JsonParser – Parse JSON String. Writing JSON using JsonGenerator Using JsonGenerator is pretty simple. First create the JsonGenerator using JsonFactory.createJsonGenerator() method and use it”s write***() methods to write each json value. JsonFactory jsonFactory = new JsonFactory(); JsonGenerator jsonGenerator = jsonFactory.createGenerator(new File( “student.json”), JsonEncoding.UTF8); // { jsonGenerator.writeStartObject(); // “name” : “Mahesh Kumar” jsonGenerator.writeStringField(“name”, “Mahesh Kumar”); Let”s see JsonGenerator in action. Create a java class file named JacksonTester in C:>Jackson_WORKSPACE. File: JacksonTester.java import java.io.File; import java.io.IOException; import java.util.Map; import com.fasterxml.jackson.core.JsonEncoding; import com.fasterxml.jackson.core.JsonFactory; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonParseException; import com.fasterxml.jackson.databind.JsonMappingException; import com.fasterxml.jackson.databind.ObjectMapper; public class JacksonTester { public static void main(String args[]){ try { JsonFactory jsonFactory = new JsonFactory(); JsonGenerator jsonGenerator = jsonFactory.createGenerator(new File(“student.json”), JsonEncoding.UTF8); jsonGenerator.writeStartObject(); // “name” : “Mahesh Kumar” jsonGenerator.writeStringField(“name”, “Mahesh Kumar”); // “age” : 21 jsonGenerator.writeNumberField(“age”, 21); // “verified” : false jsonGenerator.writeBooleanField(“verified”, false); // “marks” : [100, 90, 85] jsonGenerator.writeFieldName(“marks”); // [ jsonGenerator.writeStartArray(); // 100, 90, 85 jsonGenerator.writeNumber(100); jsonGenerator.writeNumber(90); jsonGenerator.writeNumber(85); // ] jsonGenerator.writeEndArray(); jsonGenerator.writeEndObject(); jsonGenerator.close(); //result student.json //{ // “name”:”Mahesh Kumar”, // “age”:21, // “verified”:false, // “marks”:[100,90,85] //} ObjectMapper mapper = new ObjectMapper(); Map<String,Object> dataMap = mapper.readValue(new File(“student.json”), Map.class); System.out.println(dataMap.get(“name”)); System.out.println(dataMap.get(“age”)); System.out.println(dataMap.get(“verified”)); System.out.println(dataMap.get(“marks”)); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } Verify the result Compile the classes using javac compiler as follows: C:Jackson_WORKSPACE>javac JacksonTester.java Now run the jacksonTester to see the result: C:Jackson_WORKSPACE>java JacksonTester Verify the Output Mahesh Kumar 21 false [100, 90, 85] Reading JSON using JsonParser Using JsonParser is again pretty simple. First create the JsonParser using JsonFactory.createJsonParser() method and use it”s nextToken() methods to read each json string as token. Check each token and process accordingly JsonFactory jasonFactory = new JsonFactory(); JsonParser jsonParser = jasonFactory.createJsonParser(new File(“student.json”)); while (jsonParser.nextToken() != JsonToken.END_OBJECT) { //get the current token String fieldname = jsonParser.getCurrentName(); if (“name”.equals(fieldname)) { //move to next token jsonParser.nextToken(); System.out.println(jsonParser.getText()); } } Let”s see JsonParser in action. Create a java class file named JacksonTester in C:>Jackson_WORKSPACE. File: JacksonTester.java import java.io.File; import java.io.IOException; import java.util.Map; import com.fasterxml.jackson.core.JsonEncoding; import com.fasterxml.jackson.core.JsonFactory; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonParseException; import com.fasterxml.jackson.databind.JsonMappingException; import com.fasterxml.jackson.databind.ObjectMapper; public class JacksonTester { public static void main(String args[]){ JacksonTester tester = new JacksonTester(); try { JsonFactory jsonFactory = new JsonFactory(); JsonGenerator jsonGenerator = jsonFactory.createGenerator(new File( “student.json”), JsonEncoding.UTF8); jsonGenerator.writeStartObject(); jsonGenerator.writeStringField(“name”, “Mahesh Kumar”); jsonGenerator.writeNumberField(“age”, 21); jsonGenerator.writeBooleanField(“verified”, false); jsonGenerator.writeFieldName(“marks”); jsonGenerator.writeStartArray(); // [ jsonGenerator.writeNumber(100); jsonGenerator.writeNumber(90); jsonGenerator.writeNumber(85); jsonGenerator.writeEndArray(); jsonGenerator.writeEndObject(); jsonGenerator.close(); //result student.json //{ // “name”:”Mahesh Kumar”, // “age”:21, // “verified”:false, // “marks”:[100,90,85] //} JsonParser jsonParser = jsonFactory.createParser(new File(“student.json”)); while (jsonParser.nextToken() != JsonToken.END_OBJECT) { //get the current token String fieldname = jsonParser.getCurrentName(); if (“name”.equals(fieldname)) { //move to next token jsonParser.nextToken(); System.out.println(jsonParser.getText()); } if(“age”.equals(fieldname)){ //move to next token jsonParser.nextToken(); System.out.println(jsonParser.getNumberValue()); } if(“verified”.equals(fieldname)){ //move to next token jsonParser.nextToken(); System.out.println(jsonParser.getBooleanValue()); } if(“marks”.equals(fieldname)){ //move to [ jsonParser.nextToken(); // loop till token equal to “]” while (jsonParser.nextToken() != JsonToken.END_ARRAY) { System.out.println(jsonParser.getNumberValue()); } } } } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } Verify the result Compile the classes using javac compiler as follows: C:Jackson_WORKSPACE>javac JacksonTester.java Now run the jacksonTester to see the result: C:Jackson_WORKSPACE>java JacksonTester Verify the Output Mahesh Kumar 21 false [100, 90, 85] Print Page Previous Next Advertisements ”;

Jackson – Object Serialization ”; Previous Next let”s serialize a java object to a json file and then read that json file to get the object back. In this example, we”ve created Student class. We”ll create a student.json file which will have a json representation of Student object. Create a java class file named JacksonTester in C:>Jackson_WORKSPACE. File: JacksonTester.java import java.io.File; import java.io.IOException; import com.fasterxml.jackson.core.JsonGenerationException; import com.fasterxml.jackson.core.JsonParseException; import com.fasterxml.jackson.databind.JsonMappingException; import com.fasterxml.jackson.databind.ObjectMapper; public class JacksonTester { public static void main(String args[]){ JacksonTester tester = new JacksonTester(); try { Student student = new Student(); student.setAge(10); student.setName(“Mahesh”); tester.writeJSON(student); Student student1 = tester.readJSON(); System.out.println(student1); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } private void writeJSON(Student student) throws JsonGenerationException, JsonMappingException, IOException{ ObjectMapper mapper = new ObjectMapper(); mapper.writeValue(new File(“student.json”), student); } private Student readJSON() throws JsonParseException, JsonMappingException, IOException{ ObjectMapper mapper = new ObjectMapper(); Student student = mapper.readValue(new File(“student.json”), Student.class); return student; } } class Student { private String name; private int age; public Student(){} public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String toString(){ return “Student [ name: “+name+”, age: “+ age+ ” ]”; } } Verify the result Compile the classes using javac compiler as follows: C:Jackson_WORKSPACE>javac JacksonTester.java Now run the jacksonTester to see the result: C:Jackson_WORKSPACE>java JacksonTester Verify the Output Student [ name: Mahesh, age: 10 ] Print Page Previous Next Advertisements ”;

Jackson – Environment Setup ”; Previous Next Try it Option Online You really do not need to set up your own environment to start learning Guava, a JAVA based library. Reason is very simple, we already have setup Java Programming environment online, so that you can compile and execute all the available examples online at the same time when you are doing your theory work. This gives you confidence in what you are reading and to check the result with different options. Feel free to modify any example and execute it online. Try following example using Try it option available at the top right corner of the below sample code box: public class MyFirstJavaProgram { public static void main(String []args) { System.out.println(“Hello World”); } } For most of the examples given in this tutorial, you will find Try it option, so just make use of it and enjoy your learning. Local Environment Setup If you are still willing to set up your environment for Java programming language, then this section guides you on how to download and set up Java on your machine. Please follow the following steps to set up the environment. Java SE is freely available from the link Download Java. So you download a version based on your operating system. Follow the instructions to download java and run the .exe to install Java on your machine. Once you installed Java on your machine, you would need to set environment variables to point to correct installation directories: Setting up the path for windows 2000/XP: Assuming you have installed Java in c:Program Filesjavajdk directory: Right-click on ”My Computer” and select ”Properties”. Click on the ”Environment variables” button under the ”Advanced” tab. Now, alter the ”Path” variable so that it also contains the path to the Java executable. Example, if the path is currently set to ”C:WINDOWSSYSTEM32”, then change your path to read ”C:WINDOWSSYSTEM32;c:Program Filesjavajdkbin”. Setting up the path for windows 95/98/ME: Assuming you have installed Java in c:Program Filesjavajdk directory: Edit the ”C:autoexec.bat” file and add the following line at the end: ”SET PATH=%PATH%;C:Program Filesjavajdkbin” Setting up the path for Linux, UNIX, Solaris, FreeBSD: Environment variable PATH should be set to point to where the Java binaries have been installed. Refer to your shell documentation if you have trouble doing this. Example, if you use bash as your shell, then you would add the following line to the end of your ”.bashrc: export PATH=/path/to/java:$PATH” Popular Java Editors: To write your Java programs, you will need a text editor. There are even more sophisticated IDEs available in the market. But for now, you can consider one of the following: Notepad: On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad. Netbeans:is a Java IDE that is open-source and free which can be downloaded from http://www.netbeans.org/index.html. Eclipse: is also a Java IDE developed by the eclipse open-source community and can be downloaded from http://www.eclipse.org/. Download jackson archive Download the latest version of Jackson jar file from Maven Repository – Jackson. In this tutorial, jackson-core-2.8.9.jar,jackson-annotations-2.8.9.jar and jackson-databind-2.8.9.jar are downloaded and copied into C:> jackson folder. OS Archive name Windows jackson-xxx-2.8.9.jar Linux jackson-xxx-2.8.9.jar Mac jackson-xxx-2.8.9.jar Set jackson environment Set the jackson_HOME environment variable to point to the base directory location where Guava jar is stored on your machine. Assuming, we”ve extracted jackson-core-2.8.9.jar,jackson-annotations-2.8.9.jar and jackson-databind-2.8.9.jar in jackson folder on various Operating Systems as follows. OS Output Windows Set the environment variable jackson_HOME to C:jackson Linux export jackson_HOME=/usr/local/jackson Mac export jackson_HOME=/Library/jackson Set CLASSPATH variable Set the CLASSPATH environment variable to point to the jackson jar location. Assuming, we”ve stored jackson-core-2.8.9.jar,jackson-annotations-2.8.9.jar and jackson-databind-2.8.9.jar in jackson folder on various Operating Systems as follows. OS Output Windows Set the environment variable CLASSPATH to %CLASSPATH%;%jackson_HOME%jackson-core-2.8.9.jar;%jackson_HOME%jackson-databind-2.8.9.jar;%jackson_HOME%jackson-annotations-2.8.9.jar;.; Linux export CLASSPATH=$CLASSPATH:$jackson_HOME/jackson-core-2.8.9.jar:$jackson_HOME/jackson-databind-2.8.9.jar:$jackson_HOME/jackson-annotations-2.8.9.jar:. Mac export CLASSPATH=$CLASSPATH:$jackson_HOME/jackson-core-2.8.9.jar:$jackson_HOME/jackson-databind-2.8.9.jar:$jackson_HOME/jackson-annotations-2.8.9.jar:. Print Page Previous Next Advertisements ”;

Jackson – First Application ”; Previous Next Before going into the details of the jackson library, let”s see an application in action. In this example, we”ve created Student class. We”ll create a JSON string with student details and deserialize it to student object and then serialize it to an JSON String. Create a java class file named JacksonTester in C:>Jackson_WORKSPACE. File: JacksonTester.java import java.io.IOException; import com.fasterxml.jackson.core.JsonParseException; import com.fasterxml.jackson.databind.JsonMappingException; import com.fasterxml.jackson.databind.ObjectMapper; public class JacksonTester { public static void main(String args[]){ ObjectMapper mapper = new ObjectMapper(); String jsonString = “{“name”:”Mahesh”, “age”:21}”; //map json to student try{ Student student = mapper.readValue(jsonString, Student.class); System.out.println(student); jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(student); System.out.println(jsonString); } catch (JsonParseException e) { e.printStackTrace();} catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } class Student { private String name; private int age; public Student(){} public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String toString(){ return “Student [ name: “+name+”, age: “+ age+ ” ]”; } } Verify the result Compile the classes using javac compiler as follows: C:Jackson_WORKSPACE>javac JacksonTester.java Now run the jacksonTester to see the result: C:Jackson_WORKSPACE>java JacksonTester Verify the Output Student [ name: Mahesh, age: 21 ] { “name” : “Mahesh”, “age” : 21 } Steps to remember Following are the important steps to be considered here. Step 1: Create ObjectMapper object. Create ObjectMapper object. It is a reusable object. ObjectMapper mapper = new ObjectMapper(); Step 2: DeSerialize JSON to Object. Use readValue() method to get the Object from the JSON. Pass json string/ source of json string and object type as parameter. //Object to JSON Conversion Student student = mapper.readValue(jsonString, Student.class); Step 3: Serialize Object to JSON. Use writeValueAsString() method to get the JSON string representation of an object. //Object to JSON Conversion jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(student); Print Page Previous Next Advertisements ”;

Jackson – Quick Guide ”; Previous Next Overview Jackson is a simple java based library to serialize java objects to JSON and vice versa. Features Easy to use. – jackson API provides a high level facade to simplify commonly used use cases. No need to create mapping. – jackson API provides default mapping for most of the objects to be serialized. Performance. – jackson is quiet fast and is of low memory footprint and is suitable for large object graphs or systems. Clean JSON. – jackson creates a clean and compact JSON results which is easy to read. No Dependency. – jackson library does not require any other library apart from jdk. Open Source – jackson library is open source and is free to use. Three ways of processing JSON Jackson provides three alternative ways to process JSON Streaming API – reads and writes JSON content as discrete events. JsonParser reads the data whereas JsonGenerator writes the data. It is most powerful approach among the three and is of lowest overhead and fastest in read/write opreations. It is Analogus to Stax parser for XML. Tree Model – prepares a in-memory tree representation of the JSON document. ObjectMapper build tree of JsonNode nodes. It is most flexible approach. It is analogus to DOM parser for XML. Data Binding – converts JSON to and from POJO (Plain Old Java Object) using property accessor or using annotations. It is of two type. Simple Data Binding – Converts JSON to and from Java Maps, Lists, Strings, Numbers, Booleans and null objects. Full Data Binding – Converts JSON to and from any JAVA type. ObjectMapper reads/writes JSON for both types of data bindings. Data Binding is most convenient way and is analogus to JAXB parer for XML. Environment Setup Try it Option Online You really do not need to set up your own environment to start learning Guava, a JAVA based library. Reason is very simple, we already have setup Java Programming environment online, so that you can compile and execute all the available examples online at the same time when you are doing your theory work. This gives you confidence in what you are reading and to check the result with different options. Feel free to modify any example and execute it online. Try following example using Try it option available at the top right corner of the below sample code box: public class MyFirstJavaProgram { public static void main(String []args) { System.out.println(“Hello World”); } } For most of the examples given in this tutorial, you will find Try it option, so just make use of it and enjoy your learning. Local Environment Setup If you are still willing to set up your environment for Java programming language, then this section guides you on how to download and set up Java on your machine. Please follow the following steps to set up the environment. Java SE is freely available from the link Download Java. So you download a version based on your operating system. Follow the instructions to download java and run the .exe to install Java on your machine. Once you installed Java on your machine, you would need to set environment variables to point to correct installation directories: Setting up the path for windows 2000/XP: Assuming you have installed Java in c:Program Filesjavajdk directory: Right-click on ”My Computer” and select ”Properties”. Click on the ”Environment variables” button under the ”Advanced” tab. Now, alter the ”Path” variable so that it also contains the path to the Java executable. Example, if the path is currently set to ”C:WINDOWSSYSTEM32”, then change your path to read ”C:WINDOWSSYSTEM32;c:Program Filesjavajdkbin”. Setting up the path for windows 95/98/ME: Assuming you have installed Java in c:Program Filesjavajdk directory: Edit the ”C:autoexec.bat” file and add the following line at the end: ”SET PATH=%PATH%;C:Program Filesjavajdkbin” Setting up the path for Linux, UNIX, Solaris, FreeBSD: Environment variable PATH should be set to point to where the Java binaries have been installed. Refer to your shell documentation if you have trouble doing this. Example, if you use bash as your shell, then you would add the following line to the end of your ”.bashrc: export PATH=/path/to/java:$PATH” Popular Java Editors: To write your Java programs, you will need a text editor. There are even more sophisticated IDEs available in the market. But for now, you can consider one of the following: Notepad: On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad. Netbeans:is a Java IDE that is open-source and free which can be downloaded from http://www.netbeans.org/index.html. Eclipse: is also a Java IDE developed by the eclipse open-source community and can be downloaded from http://www.eclipse.org/. Download jackson archive Download the latest version of Jackson jar file from Maven Repository – Jackson. In this tutorial, jackson-core-2.8.9.jar,jackson-annotations-2.8.9.jar and jackson-databind-2.8.9.jar are downloaded and copied into C:> jackson folder. OS Archive name Windows jackson-xxx-2.8.9.jar Linux jackson-xxx-2.8.9.jar Mac jackson-xxx-2.8.9.jar Set jackson environment Set the jackson_HOME environment variable to point to the base directory location where Guava jar is stored on your machine. Assuming, we”ve extracted jackson-core-2.8.9.jar,jackson-annotations-2.8.9.jar and jackson-databind-2.8.9.jar in jackson folder on various Operating Systems as follows. OS Output Windows Set the environment variable jackson_HOME to C:jackson Linux export jackson_HOME=/usr/local/jackson Mac export jackson_HOME=/Library/jackson Set CLASSPATH variable Set the CLASSPATH environment variable to point to the jackson jar location. Assuming, we”ve stored jackson-core-2.8.9.jar,jackson-annotations-2.8.9.jar and jackson-databind-2.8.9.jar in jackson folder on various Operating Systems as follows. OS Output Windows Set the environment variable CLASSPATH to %CLASSPATH%;%jackson_HOME%jackson-core-2.8.9.jar;%jackson_HOME%jackson-databind-2.8.9.jar;%jackson_HOME%jackson-annotations-2.8.9.jar;.; Linux export CLASSPATH=$CLASSPATH:$jackson_HOME/jackson-core-2.8.9.jar:$jackson_HOME/jackson-databind-2.8.9.jar:$jackson_HOME/jackson-annotations-2.8.9.jar:. Mac export CLASSPATH=$CLASSPATH:$jackson_HOME/jackson-core-2.8.9.jar:$jackson_HOME/jackson-databind-2.8.9.jar:$jackson_HOME/jackson-annotations-2.8.9.jar:. First Application Before going into the details of the jackson library, let”s see an application in action. In this example, we”ve created Student class. We”ll create a JSON string with student details and deserialize it to student object and then serialize it to an JSON String. Create a java class file named JacksonTester in C:>Jackson_WORKSPACE. File: JacksonTester.java import java.io.IOException; import com.fasterxml.jackson.core.JsonParseException; import com.fasterxml.jackson.databind.JsonMappingException; import com.fasterxml.jackson.databind.ObjectMapper; public class JacksonTester { public static void main(String args[]){ ObjectMapper mapper = new ObjectMapper(); String