Welcome!

Machine Learning Authors: Ed Featherston, Liz McMillan, Elizabeth White, Dan Blacharski, William Schmarzo

Related Topics: Java IoT, Industrial IoT, @CloudExpo

Java IoT: Blog Feed Post

Solving the XML Problem with Jackson | @CloudExpo #API #Java #JSON #Cloud

Jackson is a popular library for handling JSON in Java applications, quickly becoming the de-facto standard in the ecosystem

Solving the XML Problem with Jackson
By Eugen Paraschiv

Jackson is a popular library for handling JSON in Java applications, quickly becoming the de-facto standard in the ecosystem. Starting with version 2, it has also introduced a mature XML implementation alongside its established JSON support.

Adding Jackson XML to the Project
Adding the Jackson XML module to the project only needs a single dependency - the Jackson XML module itself:

<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-xml</artifactId>
<version>2.9.0</version>
</dependency>

And in Gradle:

compile "com.fasterxml.jackson.dataformat:jackson-dataformat-xml:2.9.0"

This will automatically pull in all of the other Jackson dependencies that are needed:

Note that the Woodstox StAX library can be excluded and replaced with any other valid implementation of the StAX API.

Configuring the Jackson XML Module
Jackson is typically used by means of an ObjectMapper instance. In order to work with XML, we'll instead use the XmlMapper class. This is a direct extension of ObjectMapper and can be used as a replacement, with the exact same API we're already used to.

The absolute simplest way of working with this is to just use the default configuration:

ObjectMapper objectMapper = new XmlMapper();

However, if we need additional configuration, we can instead construct the Jackson Module manually and set it up as necessary:

JacksonXmlModule xmlModule = new JacksonXmlModule();
xmlModule.setDefaultUseWrapper(false);
ObjectMapper objectMapper = new XmlMapper(module);

As of version 2.9.0, the only configuration options for the XML Module are:

  • setDefaultUseWrapper - defines whether or not to use a wrapper for non-annotated List properties by default
  • setXMLTextElementName - defines the virtual name to use when processing character data sections - when not binding to Java beans

Due to the fact that the XmlMapper extends the standard ObjectMapper, we can essentially use all of the standard Jackson ObjectMapper configuration settings and APISs.

For example, we can configure it to produce indented output as follows:

objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

Note that some of these settings might not work with some XML implementations. For example, older versions of Jackson XML depended on Stax2Writer, which didn't support writing raw characters to the stream. This means that it doesn't support writing the raw newlines and indentations needed for the INDENT_OUTPUT feature to work.

Object Serialization
Jackson is best known for its ability to serialize POJOs into JSON and back, by means of standard conventions and - where necessary - special annotations to give clues to the Jackson library.

As already mentioned, the XmlMapper object directly replaced ObjectMapper, only it works in terms of XML instead of JSON. This means that the API is exactly the same, and it can be used as a direct replacement.

Writing XML
Writing XML is done using the various
writeValue methods that Jackson exposes. For example, marshalling some object to XML is done simply by using the writeValueAsString API:

String xml = objectMapper.writeValueAsString(input);

The standard versions of this all exist and work as expected:

  • Writing to a String
  • Writing to a Byte Array
  • Writing to a java.io.OutputStream - e.g. for streaming over a network connection
  • Writing to a java.io.Writer
  • Writing to a java.io.File

Reading XML
As we just explored, we the library handles writing to XML quite well.

We can also read XML, using the various readValue APIs that are part of provided by the ObjectMapper.

For example, reading some XML from an InputStream into a Java Bean:

MyBean bean = objectMapper.readValue(inputStream, MyBean.class);

Again, the standard versions of this all exist, and work as expected:

  • Reading from a String
  • Reading from a Byte Array
  • Reading from a java.io.InputStream - e.g. for streaming over a network connection
  • Reading from a java.io.Reader
  • Reading from a java.io.File

Jackson Annotations for Serialization
The Jackson XML module supports the full range of annotations that Jackson provides for annotating our POJOs
.

This means that we can have one single set of beans, with one set of annotations and, depending on the ObjectMapper instance, we select whether we get XML or JSON. That's a huge benefit when it comes to structuring our code, as we no longer have to worry about translating between different beans that represent essentially the same data just to get different serialization formats.

For example, given the following bean:

@JsonPropertyOrder({"age", "id", "name"})
public class Person {
@JsonProperty("_id")
private String id;

private String name;

private int age;

@JsonIgnore
private String note;
}

will produce this JSON:

{
"age":4,
"_id":"12345",
"name":"George"
}

And this XML:

<Person>
<age>4</age>
<_id>12345</_id>
<name>George</name>
</Person>

Additional Jackson Annotations for XML
The Jackson XML module adds some additional support for XML specific features.
These annotations allow us to control the XML namespace and local name for elements, including the root element, whether a field is rendered in an element or as plain text, whether the content of an element is rendered in a CData wrapper, and whether a collection should use a wrapper element or not.

@JacksonXmlProperty

@JacksonXmlProperty can be applied to any field in a bean to control the details of the element that is being rendered. This annotation allows us to determine the namespace, the local name, and whether the field is serialized as an Element or an Attribute. For example, the following bean:

For example, the following bean:

public class Person {
@JacksonXmlProperty(
isAttribute = true, namespace = "urn:stackify:jacksonxml", localName = "_id")
private String id;

@JacksonXmlProperty(namespace = "urn:stackify:jackson")
private String name;

private String note;
}

This generates the following XML output:

<Person xmlns:wstxns1="urn:stackify:jacksonxml"
wstxns1:_id="12345">
<wstxns2:name xmlns:wstxns2="urn:stackify:jackson">Graham</wstxns2:name>
<note>Hello</note>
</Person>

@JacksonXmlRootElement

The @JacksonXmlRootElement has a similar role to the @JacksonXmlProperty but for the root element of the entire document. This can only adjust the Namespace and Local name - since the root element can never be serialized as an attribute.

For example, let's look at this Java POJO:

@JacksonXmlRootElement(namespace = "urn:stackify:jacksonxml", localName = "PersonData") public class Person {
private String id;

private String name;

private String note;
}

When serialized, this will result in the following XML:

<PersonData xmlns="urn:stackify:jacksonxml">
<id xmlns="">12345</id>
<name xmlns="">Graham</name>
<note xmlns="">Hello</note>
</PersonData>

@JacksonXmlText

Next, let's have a look at the @JacksonXmlText annotation.

Simply put, this indicates that an element should be rendered as plain text without another element containing it.

For example, the following POJO:

public class Person {
private String id;

private String name;

@JacksonXmlText
private String note;
}

Will produce this simple XML output:

<Person>
<id>12345</id>
<name>Graham</name>
Hello
</Person>

Naturally, you do have to be careful using this annotation and make sure you're still generating valid XML.

@JacksonXmlCData

The @JacksonXmlCData annotation indicates that a CData wrapper should be placed around the content of the element. This can be used in conjunction with the @JacksonXmlText if desired to produce a CData wrapper without an element tag.

Let's have a look at a POJO using this annotation:

public class Person {
private String id;

@JacksonXmlCData
private String name;

@JacksonXmlText
@JacksonXmlCData
private String note;
}

This will result in the following XML:

<Person>
<id>12345</id>
<name><![CDATA[Graham]]></name>
<![CDATA[Hello]]>
</Person>

JacksonXmlElementWrapper

The @JacksonXmlElementWrapper annotation is used to override the default setting from setDefaultUseWrapper - as seen above. This can ensure that a collection either does or does not use a wrapper element, and can control what the wrapper element uses for namespace and local name.

When using wrapper elements, we get an additional element added which contains all of the elements from the collection, and when wrapper elements are not used then the individual collection elements are written directly inline:

class Wrapper {
@JacksonXmlElementWrapper(localName = "list")
private List names;
}

This will produce the following XML:

<Wrapper>
<list>
<names>John</names>
<names>Paul</names>
<names>George</names>
<names>Ringo</names>
</list>
</Wrapper>

Whereas, if the JacksonXmlElementWrapper is replaced with:

@JacksonXmlElementWrapper(useWrapping = false)

Then the XML produced won't contain the list element:

<Wrapper>
<names>John</names>
<names>Paul</names>
<names>George</names>
<names>Ringo</names>
</Wrapper>

Supporting JAXB Annotations

The Jackson XML module also has the ability to support the standard JAXB annotations on our beans - instead of needing the Jackson specific ones. This can be useful if we want to use Jackson for the actual XML Serialization but don't want to depend on it at compile time.

This can also be used to allow JAXB to generate our bean definitions from an XML Schema and have Jackson process them.

This functionality is an additional module that needs to be added in for it to work. It doesn't work out of the box like the Jackson annotations do. In order to configure this - we need to add the JaxbAnnotationModule to our ObjectMapper as follows:

objectMapper.registerModule(new JaxbAnnotationModule());

We can now write or generate a Java bean with JAXB annotations and simply process it with this XmlMapper.

For example, the following POJO:

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class EmployeeBean {
@XmlAttribute(name = "_id")
@XmlID
private String id;

@XmlElement
private String name;

@XmlElement
private String type;
}

Will produce the following XML when marshalled:

<employee _id="12345">
<name>Graham</name>
<type>Developer</type>
</employee>

Partial Reading and Writing
Jackson also has the powerful ability to actually jump into the middle of an existing XML file and either marshall or unmarshall XML to and from that file.

The functionality makes good use of the standard XMLStreamWriter class, and naturally of XMLStreamReader as well. This cool functionality gives us a lot of flexibility to work with existing XML documents and integrate with these cleanly and easily.

Generating XML
The XmlMapper is able to serialize an entire Java bean into a document that is currently being produced, allowing Jackson to integrate and construct the document along with other external actors. This also gives some ability to support constructs that Jackson cannot handle natively - for example, the XML Prolog.

In order to do this, the XmlMapper needs to be called to write values to the XMLStreamWriter object - the same as if we were writing to any other Writer:

StringWriter stringWriter = new StringWriter();
XMLOutputFactory xmlOutputFactory = XMLOutputFactory.newFactory();
XMLStreamWriter sw = xmlOutputFactory.createXMLStreamWriter(stringWriter);

XmlMapper mapper = new XmlMapper();

sw.writeStartDocument();
sw.writeStartElement("root");

mapper.writeValue(sw, employeeBean);
sw.writeComment("Some insightful commentary here");
sw.writeEndElement();
sw.writeEndDocument();

This will produce the following XML:

<?xml version='1.0' encoding='UTF-8'?>
<root>
<employee _id="12345">
<name>Graham</name>
<type>Developer</type>
</employee>
<!--Some insightful commentary here-->
</root>

Here, the XML Prolog, root element, and the comment - are not produced by Jackson XML, but everything inside the EmployeeBean element is.

Consuming XML
The opposite of this is also possible - deserializing a Java bean from the middle of an XMLStreamReader.

This can be especially useful if we only care to have Java bean representations for data in the middle of a larger object - for example, if we are parsing an Atom wrapper around the data we are interested in.

In order to do this, the XmlMapper needs to be called to read values from the XMLStreamReader object - the same as if we were reading from any other Reader.

Let's have a look at a simple example. The following Java code will consume the XML generated above into an EmployeeBeen instance:

XMLInputFactory f = XMLInputFactory.newFactory();
XMLStreamReader sr = f.createXMLStreamReader(new FileInputStream(inputFile));

XmlMapper mapper = new XmlMapper();
sr.next(); // to point to <root>
sr.next(); // to point to root-element under root
EmployeeBeen employee = mapper.readValue(sr, EmployeeBeen.class);
sr.close();

Limitations of the Jackson XML Module
The XML module in Jackson is by no means designed to be an exact replacement for JAXB. There are certain constructs that will work subtly differently between JAXB and Jackson, and there is no guarantee that Jackson will produce identical XML to JAXB.

Note that, unlike with JSON, the outermost object must be a bean type - it can not be a primitive or wrapper type, an enumeration, or a collection. This is a direct result of how XML works - there's no way in XML to represent such a top-level value.

By default, Jackson will always use a wrapper element for collections, which is also different to how JAXB works. This is the major way that the XML produced by Jackson is not compatible with the XML produced by JAXB. Of course, the behavior can be configured, using the JacksonXmlElementWrapper annotation for one field or the setDefaultUseWrapper configuration setting on the XmlMapper globally.

Jackson also has no support for working with specific XML Schemas. It's designed for writing Java Beans first, rather than generating the Java code from pre-existing schemas. Note that this can be solved to an extent by using the JAXB annotation support and generating the beans using the standard xjc tool.

Equally, it has no support for some of the more advanced XML tools - such as XPath or XSLT. If we need this level of support then we should instead use a more full-featured XML solution.

Usage on Android
In the mobile space, Jackson XML works perfectly well on Android. However, the StAX API is not included in the Android JVM, so it needs to instead be bundled manually.

If we're using the Woodstox XML library that Jackson XML depends on by default - there's nothing extra to be done. If, however, we're using an alternative library - then we might need to add that dependency manually:

<dependency>
<groupId>javax.xml.stream</groupId>
<artifactId>stax-api</artifactId>
<version>1.0-2</version>
</dependency</span>

And for Gradle:

compile "javax.xml.stream:stax-api:jar:1.0-2"

Summary
If you're looking for a mature, flexible way of supporting and working with both JSON and XML for the same data, the Jackson XML module is a fantastic library to leverage. It's not only a solid way to go on its own, but it also has the added benefit of being able to mostly reuse the same configuration for both XML as well as JSON.

Typically, this has to be handled using two different libraries with entirely separate configurations.

Finally, beyond flexibility and ease-of-use, the Jackson team has historically placed a strong emphasis on performance. And given that marshalling and unmarshalling of data is a large part of most web applications, choosing the right library to handle all of that work is critical. That, plus a performance monitoring tool such as Retrace will allow you to get the most out of your app.

The post Solving the XML Problem with Jackson appeared first on Stackify.

Read the original blog entry...

More Stories By Stackify Blog

Stackify offers the only developers-friendly solution that fully integrates error and log management with application performance monitoring and management. Allowing you to easily isolate issues, identify what needs to be fixed quicker and focus your efforts – Support less, Code more. Stackify provides software developers, operations and support managers with an innovative cloud based solution that gives them DevOps insight and allows them to monitor, detect and resolve application issues before they affect the business to ensure a better end user experience. Start your free trial now stackify.com

@CloudExpo Stories
"Storpool does only block-level storage so we do one thing extremely well. The growth in data is what drives the move to software-defined technologies in general and software-defined storage," explained Boyan Ivanov, CEO and co-founder at StorPool, in this SYS-CON.tv interview at 16th Cloud Expo, held June 9-11, 2015, at the Javits Center in New York City.
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
As DevOps methodologies expand their reach across the enterprise, organizations face the daunting challenge of adapting related cloud strategies to ensure optimal alignment, from managing complexity to ensuring proper governance. How can culture, automation, legacy apps and even budget be reexamined to enable this ongoing shift within the modern software factory? In her Day 2 Keynote at @DevOpsSummit at 21st Cloud Expo, Aruna Ravichandran, VP, DevOps Solutions Marketing, CA Technologies, was jo...
As Marc Andreessen says software is eating the world. Everything is rapidly moving toward being software-defined – from our phones and cars through our washing machines to the datacenter. However, there are larger challenges when implementing software defined on a larger scale - when building software defined infrastructure. In his session at 16th Cloud Expo, Boyan Ivanov, CEO of StorPool, provided some practical insights on what, how and why when implementing "software-defined" in the datacent...
Blockchain. A day doesn’t seem to go by without seeing articles and discussions about the technology. According to PwC executive Seamus Cushley, approximately $1.4B has been invested in blockchain just last year. In Gartner’s recent hype cycle for emerging technologies, blockchain is approaching the peak. It is considered by Gartner as one of the ‘Key platform-enabling technologies to track.’ While there is a lot of ‘hype vs reality’ discussions going on, there is no arguing that blockchain is b...
Blockchain is a shared, secure record of exchange that establishes trust, accountability and transparency across business networks. Supported by the Linux Foundation's open source, open-standards based Hyperledger Project, Blockchain has the potential to improve regulatory compliance, reduce cost as well as advance trade. Are you curious about how Blockchain is built for business? In her session at 21st Cloud Expo, René Bostic, Technical VP of the IBM Cloud Unit in North America, discussed the b...
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
Is advanced scheduling in Kubernetes achievable?Yes, however, how do you properly accommodate every real-life scenario that a Kubernetes user might encounter? How do you leverage advanced scheduling techniques to shape and describe each scenario in easy-to-use rules and configurations? In his session at @DevOpsSummit at 21st Cloud Expo, Oleg Chunikhin, CTO at Kublr, answered these questions and demonstrated techniques for implementing advanced scheduling. For example, using spot instances and co...
The cloud era has reached the stage where it is no longer a question of whether a company should migrate, but when. Enterprises have embraced the outsourcing of where their various applications are stored and who manages them, saving significant investment along the way. Plus, the cloud has become a defining competitive edge. Companies that fail to successfully adapt risk failure. The media, of course, continues to extol the virtues of the cloud, including how easy it is to get there. Migrating...
The use of containers by developers -- and now increasingly IT operators -- has grown from infatuation to deep and abiding love. But as with any long-term affair, the honeymoon soon leads to needing to live well together ... and maybe even getting some relationship help along the way. And so it goes with container orchestration and automation solutions, which are rapidly emerging as the means to maintain the bliss between rapid container adoption and broad container use among multiple cloud host...
Imagine if you will, a retail floor so densely packed with sensors that they can pick up the movements of insects scurrying across a store aisle. Or a component of a piece of factory equipment so well-instrumented that its digital twin provides resolution down to the micrometer.
The need for greater agility and scalability necessitated the digital transformation in the form of following equation: monolithic to microservices to serverless architecture (FaaS). To keep up with the cut-throat competition, the organisations need to update their technology stack to make software development their differentiating factor. Thus microservices architecture emerged as a potential method to provide development teams with greater flexibility and other advantages, such as the abili...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settle...
Product connectivity goes hand and hand these days with increased use of personal data. New IoT devices are becoming more personalized than ever before. In his session at 22nd Cloud Expo | DXWorld Expo, Nicolas Fierro, CEO of MIMIR Blockchain Solutions, will discuss how in order to protect your data and privacy, IoT applications need to embrace Blockchain technology for a new level of product security never before seen - or needed.
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
In his general session at 21st Cloud Expo, Greg Dumas, Calligo’s Vice President and G.M. of US operations, discussed the new Global Data Protection Regulation and how Calligo can help business stay compliant in digitally globalized world. Greg Dumas is Calligo's Vice President and G.M. of US operations. Calligo is an established service provider that provides an innovative platform for trusted cloud solutions. Calligo’s customers are typically most concerned about GDPR compliance, application p...
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...