Generate Java class from JSON

Question

In a Java Maven project  how do you generate java source files from JSON  For example we have         firstName    John        lastName    Smith        address            streetAddress    21 2nd Street           city    New York          When we run mvn generate-sources we want it to generate something like this     class Address        JSONObject mInternalJSONObject       Address  JSONObject json           mInternalJSONObject   json             String  getStreetAddress              return mInternalJSONObject getString  streetAddress               String  getCity             return mInternalJSONObject getString  city             class Person               JSONObject mInternalJSONObject       Person  JSONObject json           mInternalJSONObject   json             String  getFirstName              return mInternalJSONObject getString  firstName               String  getLastName             return mInternalJSONObject getString  lastName               Address getAddress             return Address mInternalJSONObject getString  address               As a Java developer  what lines of XML do I need to write in my pom xml in order to make this happen

User · Answer

You could also try GSON library  Its quite powerful it can create JSON from collections  custom objects and works also vice versa   Its released under Apache Licence 2 0 so you can use it also commercially    http   code google com p google-gson

User · Answer

Try my solution  http   htmlpreview github io  https   raw githubusercontent com foobnix android-universal-utils master json generator html         auctionHouse    sample string 1        bidDate    2014-05-30T08 20 38 5426521-04 00         bidPrice   3       bidPrice1   3 1       isYear  true     Result Java Class  private String  auctionHouse  private Date  bidDate  private int  bidPrice  private double  bidPrice1  private boolean  isYear    JSONObject get   auctionHouse   obj getString  auctionHouse    bidDate   obj opt  bidDate    bidPrice   obj getInt  bidPrice    bidPrice1   obj getDouble  bidPrice1    isYear   obj getBoolean  isYear      JSONObject put  obj put  auctionHouse  auctionHouse   obj put  bidDate  bidDate   obj put  bidPrice  bidPrice   obj put  bidPrice1  bidPrice1   obj put  isYear  isYear

User · Answer

If you re using Jackson  the most popular library there   try https   github com astav JsonToJava Its open source  last updated on Jun 7  2013 as of year 2020  and anyone should be able to contribute  Summary A JsonToJava source class file generator that deduces the schema based on supplied sample json data and generates the necessary java data structures  It encourages teams to think in Json first  before writing actual code  Features  Can generate classes for an arbitrarily complex hierarchy  recursively  Can read your existing Java classes and if it can deserialize into those structures  will do so Will prompt for user input when ambiguous cases exist

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I created a github project Json2Java that does this  https   github com inder123 json2java  Json2Java provides customizations such as renaming fields  and creating inheritance hierarchies   I have used the tool to create some relatively complex APIs   Gracenote s TMS API  https   github com inder123 gracenote-java-api  Google Maps Geocoding API  https   github com inder123 geocoding

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Let me show you how to dev the tool you can do so    user javascript function Json parse   make string like-json trans to js object then use this object to genrate the javabean format  something you shoud care  1 value type mapping forexample how to figure out the string is date type  2 loweser case to camelCase    I dev a tool solve the problem it is well design and quick more  get the code from my github   enjoy it from here I have deploy it on webserver   I try the top 2 answer s suggestion one web is can not open one is slower than my tool hope you will enjoy my tool

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I m aware this is an old question  but I stumbled across it while trying to find an answer myself    The answer that mentions the online json-pojo generator  jsongen  is good  but I needed something I could run on the command line and tweak more   So I wrote a very hacky ruby script to take a sample JSON file and generate POJOs from it   It has a number of limitations  for example  it doesn t deal with fields that match java reserved  keywords  but it does enough for many cases   The code generated  by default  annotates for use with Jackson  but this can be turned off with a switch   You can find the code on github  https   github com wotifgroup json2pojo

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As far as I know there is no such tool  Yet   The main reason is  I suspect  that unlike with XML  which has XML Schema  and then tools like  xjc  to do what you ask  between XML and POJO definitions   there is no fully features schema language  There is JSON Schema  but it has very little support for actual type definitions  focuses on JSON structures   so it would be tricky to generate Java classes  But probably still possible  esp  if some naming conventions were defined and used to support generation   However  this is something that has been fairly frequently requested  on mailing lists of JSON tool projects I follow   so I think that someone will write such a tool in near future   So I don t think it is a bad idea per se  also  it is not a good idea for all use cases  depends on what you want to do

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Answering this old question with recent project  -    At the moment the best solution is probably JsonSchema2Pojo     It does the job from the seldom used Json Schema but also with plain Json  It provides Ant and Maven plugin and an online test application can give you an idea of the tool  I put a Json Tweet and generated all the containing class  Tweet  User  Location  etc      We ll use it on Agorava project to generate Social Media mapping and follow the contant evolution in their API

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Thanks all who attempted to help  For me this script was helpful  It process only flat JSON and don t take care of types  but automate some routine    String str                                title    Computing and Information systems                    id    1                   children     true                    groups                            title     Level one CIS                        id    2                       children     true                        groups                                title     Intro To Computing and Internet                            id    3                           children    false                            groups                                                                       JSONObject json   new JSONObject str       Iterator lt String gt  iterator    json keys         System out println  Fields         while  iterator hasNext             System out println String format  public String  s    iterator next                 System out println  public void Parse  String str          System out println  JSONObject json   new JSONObject str           iterator    json keys        while  iterator hasNext             String key   iterator next           System out println String format  this  s   json getString    s      key key          System out println

User · Answer

Try http   www jsonschema2pojo org Or the jsonschema2pojo plug-in for Maven           lt plugin gt               lt groupId gt org jsonschema2pojo lt  groupId gt               lt artifactId gt jsonschema2pojo-maven-plugin lt  artifactId gt               lt version gt 1 0 2 lt  version gt               lt configuration gt                   lt sourceDirectory gt   basedir  src main resources schemas lt  sourceDirectory gt                   lt targetPackage gt com myproject jsonschemas lt  targetPackage gt                   lt sourceType gt json lt  sourceType gt               lt  configuration gt               lt executions gt                   lt execution gt                       lt goals gt                           lt goal gt generate lt  goal gt                       lt  goals gt                   lt  execution gt               lt  executions gt           lt  plugin gt   The  lt sourceType gt json lt  sourceType gt  covers the case where the sources are json  like the OP   If you have actual json schemas  remove this line  Updated in 2014  Two things have happened since Dec  09 when this question was asked   The JSON Schema spec has moved on a lot  It s still in draft  not finalised  but it s close to completion and is now a viable tool specifying your structural rules  I ve recently started a new open source project specifically intended to solve your problem  jsonschema2pojo  The jsonschema2pojo tool takes a json schema document and generates DTO-style Java classes  in the form of  java source files   The project is not yet mature but already provides coverage of the most useful parts of json schema  I m looking for more feedback from users to help drive the development  Right now you can use the tool from the command line or as a Maven plugin    Hope this helps

User · Answer

To add to  japher s post  If you are not particularly tied to JSON  Protocol Buffers is worth checking out

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I had the same problem so i decided to start writing a small tool to help me with this  Im gonna share andopen source it   https   github com BrunoAlexandreMendesMartins CleverModels  It supports  JAVA  C   amp  Objective-c from JSON    Feel free to contribute

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Here s an online tool that will take JSON  including nested objects or nested arrays of objects and generate a Java source with Jackson annotations

[java] Generate Java class from JSON?

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