Parsing Json File using Jackson

Question

{
   "TestSuite":{
      "TestSuiteInfo":{
         "-description":"parse"
      },
      "TestCase":[
         {
            "TestCaseData":{
               "-sequence":"sequential",
               "-testNumber":"2",
               "-testCaseFile":"testcase\\Web\\Ab.xml"
            }
         },
         {
            "TestCaseData":{
               "-sequence":"sequential",
               "-testNumber":"3",
               "-testCaseFile":"testcase\\Web\\BC.xml"
            }
         }
      ]
   }
}

My Pojos are:

public class TestSuite {    

    private TestSuiteInfo testSuiteInfo;
    private TestCase listOfTestCases;

    public TestSuiteInfo getTestSuiteInfo() {   
        return testSuiteInfo;
    }

    public void setTestSuiteInfo(TestSuiteInfo testSuiteInfo) {
        this.testSuiteInfo = testSuiteInfo;
    }

    public TestCase getListOfTestCases() {
        return listOfTestCases;
    }

    public void setListOfTestCases(TestCase listOfTestCases) {
        this.listOfTestCases = listOfTestCases;
    }
}


public class TestSuiteInfo {

    private String description;

    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
}


import java.util.Iterator;
import java.util.List;

public class TestCase {

    private List<TestCaseData> testCaseData;

    public List<TestCaseData> getTestCaseData() {
        return testCaseData;
    }

    public void setTestCaseData(List<TestCaseData> testCaseData) {
        this.testCaseData = testCaseData;
    }
}


public class TestCaseData {

    private String sequence;
    private int testNumber;
    private String testCaseFile;

    public String getSequence() {   
        return sequence;
    }

    public void setSequence(String sequence) {
        this.sequence = sequence;
    }

    public int getTestNumber() {
        return testNumber;
    }

    public void setTestNumber(int testNumber) {
        this.testNumber = testNumber;
    }

    public String getTestCaseFile() {
        return testCaseFile;
    }

    public void setTestCaseFile(String testCaseFile) {
        this.testCaseFile = testCaseFile;
    }
}

I haven't use Jackson before, will really appreciate if anyone could help me in parsing the file and getting the objects. I am trying to parse this from past two days, but didnt got any success

Answer 1

Usually to parse JSON with the Jackson library, you would use the ObjectMapper class like this:

public static void main(final String[] args) {
    final String json = "some JSON string";
    final ObjectMapper mapper = new ObjectMapper();
    final TestSuite readValue = mapper.readValue(json, TestSuite.class);
    //Then some code that uses the readValue.
    //Keep in mind that the mapper.readValue() method does throw some exceptions
    //So you'll need to handle those too.    
}

However, I wrote a quick test class to check out the parsing of your JSON and came across some issues.

Basically, the design of the JSON and the design of the domain don't match up. So you can either alter the JSON, or you can alter the domain objects.

Altering the JSON to fit the domain

1. The property names that have "-" in them wont parse nicely in jackson, so they will need to be removed.
2. Having the class name before eachof the objects isn't going to help. Jackson will expect these to be properties, so the Class names will need removing or replacing with property names.
3. Property names must be provided as they are in the domain objects in order for jackson to parse them. You can't just say here's an object and then start a list, the list must have a property name/

After I'd adjusted a these things in the JSON, I got it to parse with the provided domain objects. The JSON I ended up with looked like this:

{
   "testSuiteInfo":{
      "description":"parse"
   },
   "listOfTestCases":{
      "testCaseData":[
         {
            "sequence":"sequential",
            "testNumber":"2",
            "testCaseFile":"testcase\\Web\\Ab.xml"
         },
         {
            "sequence":"sequential",
            "testNumber":"3",
            "testCaseFile":"testcase\\Web\\BC.xml"
         }
      ]
   }
}

Here's my test method that does parse the doctored JSON above (please ignore all the escape characters)

public static void main(final String[] args) {
    final String json = "{\"testSuiteInfo\":{\"description\":\"parse\"}," +
            "\"listOfTestCases\":{" +
            "\"testCaseData\":[" +
            "{\"sequence\":\"sequential\",\"testNumber\":\"2\",\"testCaseFile\":\"testcase\\\\Web\\\\Ab.xml\"}," +
            "{\"sequence\":\"sequential\",\"testNumber\":\"3\",\"testCaseFile\":\"testcase\\\\Web\\\\BC.xml\"}" +
            "]" +
            "}" +
            "}";

    final ObjectMapper mapper = new ObjectMapper();

    try {
        final TestSuite readValue = mapper.readValue(json, TestSuite.class);
        System.out.println(readValue.getListOfTestCases()); //just a test to see if the object is built
    }
    catch (final Exception e) {
        e.printStackTrace();
    }
}

Altering the domain to fit the JSON

Firstly, the main issues is having the Class names as the property identifiers. That makes it quite difficult to work with this JSON in the usual manner. I've had to add a couple of wrapper classes to get around the class names being in the JSON.

• I've added an OverallWrapper class that has a TestSuite property to cater for the TestSuite class name in the JSON.

• I've also added a TestCaseDataWrapper class to cater for the TestCaseData class names in the list in the JSON.

• I removed the TestCase class all together as that just became a property on one of the other classes.

• Then to make the property names match up with the objects, I've used the @JsonProperty annotation.

Here are the classes after the modifications, and the ultimate parser test method that works and parses the JSON. (again, excuse all the escape characters in the JSON string)

import org.codehaus.jackson.annotate.JsonProperty;         

public class OverallWrapper {                              

    private TestSuite testSuite;                           

    @JsonProperty("TestSuite")                             
    public TestSuite getTestSuite() {                      
        return this.testSuite;                             
    }                                                      

    public void setTestSuite(final TestSuite testSuite) {  
        this.testSuite = testSuite;                        
    }                                                      
}



import java.util.List;                                                                                                                                  
import org.codehaus.jackson.annotate.JsonProperty;                              

public class TestSuite {                                                        

    private TestSuiteInfo testSuiteInfo;                                        

    private List<TestCaseDataWrapper> testCaseData;                             

    @JsonProperty("TestCase")                                                   
    public List<TestCaseDataWrapper> getTestCaseData() {                        
        return this.testCaseData;                                               
    }                                                                           

    public void setTestCaseData(final List<TestCaseDataWrapper> testCaseData) { 
        this.testCaseData = testCaseData;                                       
    }                                                                           

    @JsonProperty("TestSuiteInfo")                                              
    public TestSuiteInfo getTestSuiteInfo() {                                   
        return this.testSuiteInfo;                                              
    }                                                                           

    public void setTestSuiteInfo(final TestSuiteInfo testSuiteInfo) {           
        this.testSuiteInfo = testSuiteInfo;                                     
    }                                                                                                                                                   
}          



import org.codehaus.jackson.annotate.JsonProperty;          

public class TestSuiteInfo {                                

    private String description;                             

    @JsonProperty("-description")                           
    public String getDescription() {                        
        return this.description;                            
    }                                                       
    public void setDescription(final String description) {  
        this.description = description;                     
    }                                                       
}                                                                                                                                



import org.codehaus.jackson.annotate.JsonProperty;                  

public class TestCaseDataWrapper {                                  

    @JsonProperty("TestCaseData")                                   
    private TestCaseData testcaseData;                              

    public TestCaseData getTestcaseData() {                         
        return this.testcaseData;                                   
    }                                                               

    public void setTestcaseData(final TestCaseData testcaseData) {  
        this.testcaseData = testcaseData;                           
    }                                                               
}       



import org.codehaus.jackson.annotate.JsonProperty;             

public class TestCaseData {                                    

    private String sequence;                                   
    private int testNumber;                                    
    private String testCaseFile;                               

    @JsonProperty("-sequence")                                 
    public String getSequence() {                              
        return this.sequence;                                  
    }                                                          

    public void setSequence(final String sequence) {           
        this.sequence = sequence;                              
    }                                                          

    @JsonProperty("-testNumber")                               
    public int getTestNumber() {                               
        return this.testNumber;                                
    }                                                          

    public void setTestNumber(final int testNumber) {          
        this.testNumber = testNumber;                          
    }                                                          

    @JsonProperty("-testCaseFile")                             
    public String getTestCaseFile() {                          
        return this.testCaseFile;                              
    }                                                          

    public void setTestCaseFile(final String testCaseFile) {   
        this.testCaseFile = testCaseFile;                      
    }                                                          
}                                                              



public static void main(final String[] args) {

    final String json = "{\"TestSuite\":{\"TestSuiteInfo\":{\"-description\":\"parse\"},\"TestCase\":[" +
            "{\"TestCaseData\":{\"-sequence\":\"sequential\",\"-testNumber\":\"2\",\"-testCaseFile\":\"testcase\\\\Web\\\\Ab.xml\"}}," +
            "{\"TestCaseData\":{\"-sequence\":\"sequential\",\"-testNumber\":\"3\",\"-testCaseFile\":\"testcase\\\\Web\\\\BC.xml\"}}" +
            "]}}";

    final ObjectMapper mapper = new ObjectMapper();

    try {
        final OverallWrapper readValue = mapper.readValue(json, OverallWrapper.class);

        System.out.println(readValue.getTestSuite());
    }
    catch (final Exception e) {
        e.printStackTrace();
    }
}

Summing up

The ultimate issue is that the domain doesn't marry up with the JSON.

Personally I prefer to change the JSON to marry up to the domain, as the domain seems to make sense in it's design and requires less customization and forcing.

However, I do accept that you may not have that choice, hence the redesign of the domain.

Answer 2

In this blog you can find a simple way to parse a large json file without directly using Jackson's ObjectMapper https://www.ngdata.com/parsing-a-large-json-file-efficiently-and-easily/

With jp.skipChildren() and nested loops you can reach to your section of interest and once you are there simply break the nested loops using a label:

outerloop: while (jp.nextToken() != JsonToken.END_OBJECT) {
  //...nested loops here
  break outerloop;
  //...closing loops
}

I copied the code for reference:

import org.codehaus.jackson.map.*;
import org.codehaus.jackson.*;

import java.io.File;

public class ParseJsonSample {
  public static void main(String[] args) throws Exception {
    JsonFactory f = new MappingJsonFactory();
    JsonParser jp = f.createJsonParser(new File(args[0]));

    JsonToken current;

    current = jp.nextToken();
    if (current != JsonToken.START_OBJECT) {
      System.out.println("Error: root should be object: quiting.");
      return;
    }

    while (jp.nextToken() != JsonToken.END_OBJECT) {
      String fieldName = jp.getCurrentName();
      // move from field name to field value
      current = jp.nextToken();
      if (fieldName.equals("records")) {
        if (current == JsonToken.START_ARRAY) {
          // For each of the records in the array
          while (jp.nextToken() != JsonToken.END_ARRAY) {
            // read the record into a tree model,
            // this moves the parsing position to the end of it
            JsonNode node = jp.readValueAsTree();
            // And now we have random access to everything in the object
            System.out.println("field1: " + node.get("field1").getValueAsText());
            System.out.println("field2: " + node.get("field2").getValueAsText());
          }
        } else {
          System.out.println("Error: records should be an array: skipping.");
          jp.skipChildren();
        }
      } else {
        System.out.println("Unprocessed property: " + fieldName);
        jp.skipChildren();
      }
    }                
  }
}

From the blog:

The nextToken() call each time gives the next parsing event: start object, start field, start array, start object, …, end object, …, end array, …

The jp.skipChildren() is convenient: it allows to skip over a complete object tree or an array without having to run yourself over all the events contained in it.

All the credits go to the blog's author: Molly Galetto