Extracting data from a JSON file/URL/Object/String in Java

[Daniel Ross]

Hi there,

I hope someone can help me out as I am really struggling for this.

Basically what I am looking for is to be able to extract data properly from a json file or string or object or anything else in that format.

I found many tutorials/guide but nothing that could help me really.

I can read a json url but once I have the content I want to properly separate it so I can display it in a more readable format.

How do I do this in java? and what is the best parser to do this?

Thank you

[Saifuddin Merchant]

Jackson is the usual JSON parser used in java - http://jackson.codehaus.org/
They got a tutorial and stuff on how to use it.

[Daniel Ross]

Thank you for the reply.

If I put the code in the following way then it gives me an error on the first line

public class readJson throws JsonParseException, IOException

public class readJson throws JsonParseException, IOException {
	
	public readJson()
	{
		
	}
	
	String str="";
	JsonFactory f= new JsonFactory();
	JsonParser jp=f.createJsonParser(new File("try")); 

}

it doesn't give my any error if I put it in this way

public class readJson  {
	
	public readJson()throws JsonParseException, IOException
	{
		String str="";
		JsonFactory f= new JsonFactory();
		JsonParser jp=f.createJsonParser(new File("try")); 
	}
	
}

Why so?
ps: @Bear sorry about it, I amended the name now.

[John de Michele]

Daniel:

A few things:

1. Java classes start with capitals, so the class should be ReadJson, not readJson.
2. You can't have code outside of a method (hint: see line 10 of your erroring class)
3. Classes don't throw exceptions, methods do.

John.

[Stephan van Hulst]

Well, class names should be nouns, so the name should really be JsonReader.

[Daniel Ross]

Hi yes I realized it and already change it .

Thanks for the info

I manage to separate the json file, so now I can show each token separately.
What I am trying to do is to to save the number of users and their details from the json string
Here is the user class I made

public class User {
	
	
	private String completed_in;
	private String strQuery;
	private UserID _userid;
	
	public static class UserID{
		
		private String created_at;
		private String from_user;
		private String user_id;
		private String geo;
		private String text;
		
		
		public String getCreated_at(){ return created_at;}
		public String getFrom_user(){ return from_user;}
		public String getUser_id(){ return user_id;}
		public String getGeo(){ return geo;}
		public String getText(){ return text;}
		
		
		public void SetCreated_at(String s) {created_at=s;}
		public void SetFrom_user(String s) {from_user=s;}
		public void SetUser_id(String s) {user_id=s;}
		public void SetGeo(String s) {geo=s;}
		public void SetText(String s) {text=s;}
		
	}
	public String getCompleted_in(){ return completed_in;}
	public String getStrQuery(){ return strQuery;}

	public void SetCompleted_in(String s) {completed_in=s;}
	public void SetStrQuery(String s) {strQuery=s;}
	
	public void setUserID(UserID n){_userid=n;}
	
}

This class has all the variables, the string I want to get the data from has details such as when the file was created and all the users in that file.
I want to store the data in a way that it shows :
Completed in: times
query: the search query used
Number of users: integer
name:
user id:
geo:
etc.....
and then show the user two details
show the user 3 details etc....

How do I save it so that users are saved in an array calling the User class I have created.

Here is the code I am trying to make but I don't know how to continue:

ArrayList<String> al=new ArrayList<String>();
		JsonFactory f= new JsonFactory();
		JsonParser jp=f.createJsonParser(str); 
	
		jp.nextToken();
		
		User user=new User();
		User.UserID userid=new User.UserID();
		//ArrayList<User> users=new ArrayList<User>();
		
		String nameField;
/*
 here i go in a loop which goes through the whole json string and when it finds a token
 that is equal to the namefield then it will set that name by calling the class,
 however I am not sure how to use it and properly interact with the class to save it properly.
 */
		while (jp.nextToken() != null) {
		nameField=jp.getCurrentName();
		jp.nextToken();
		if("Completed_in".equalsIgnoreCase(nameField))	{ user.SetCompleted_in(jp.getText());}
		else if
		("query".equalsIgnoreCase(nameField)){user.SetStrQuery(jp.getText());}
		else if
		("query".equalsIgnoreCase(nameField)){user.SetStrQuery(jp.getText());}
		
		
		else {
	        throw new IllegalStateException("Unrecognized field '"+nameField+"'!");
	      }
		

[Edit]Hope you haven’t used line numbers; your comment was so long and difficult to read, that I divided it into 5 lines. CR[/edit]

[Daniel Ross]

hey

This is the code I am using to save it in an array but with no success

First I made an instance of the UsedID class in an array

User.UserID[] userid=new User.UserID[100];

I, then stored the value in by calling that class in the same way as I done with the other values ,but in this case it's an array.

if("from_user".equalsIgnoreCase(nameField))
		{
			userid[uc].SetFrom_user(nameField); //however I get an error here,it seems that it doesn't accept it when I run this piece of code.
			uc++;
			
		}

[John de Michele]

Daniel:

Another niggly style issue: member variable names should be in Camel Case, starting with a lowercase letter. Underscores between words should be avoided, unless you're doing a static final in all uppercase.

John.

[Campbell Ritchie]

John de Michele wrote:Daniel:

Another niggly style issue: . . . .

You are also using inconsistent indentation. Don’t use tabs for indenting. Use spaces. Follow the keyword if with a single space. Don’'t try to compress a method into one line. A “getXXX” method returning a boolean should be called “isXXX” or “hasXXX”.
All little things, but inconsistencies make it harder to read your code.