i am a beginner of hadoop,i have been told to create a custom inputformat class to read json data,i have googled up and learnt how to create a custom inputformat class to read data from the file.but i am stuck on parsing the json data. my json data looks like this
[
{
"_count": 30,
"_start": 0,
"_total": 180,
"values": [
{
"attachment": {
"contentDomain": "techcarnival2013.eventbrite.com",
"contentUrl": "http://techcarnival2013.eventbrite.com/",
"imageUrl": "http://ebmedia.eventbrite.com/s3-s3/static/images/django/logos/eb_home_tm-trans-fb.png",
"summary": "Get to know a few thousand of Silicon Valley's best and brightest while enjoying unparalleled access to Candlestick Park,\u00a0games, food, music and more. We'll have carnival games you haven't played since you were ten, giant inflatable obstacle...",
"title": "Tech Carnival @ Candlestick Park"
},
"comments": {
"_total": 0
},
"creationTimestamp": 1373908436000,
"creator": {
"firstName": "Clayton",
"headline": "Director of Operations",
"secondname":{
"name":"myname"
},
"lastName": "K.",
"pictureUrl": "http://m.c.lnkd.licdn.com/mpr/mprx/0_R7Vm6_RqBDHaHCDzJHRA6hsNcwOfECjzMeaA6heqHeo0v6ovBWoCe8pVJiYrd5pJVu4KdbnQQ3Lj"
},
"likes": {
"_total": 0
},
"relationToViewer": {
"availableActions": {
"_total": 7,
"values": [
{
"code": "add-comment"
},
{
"code": "categorize-as-job"
},
{
"code": "categorize-as-promotion"
},
{
"code": "flag-as-inappropriate"
},
{
"code": "follow"
},
{
"code": "like"
},
{
"code": "reply-privately"
}
]
},
"isFollowing": false,
"isLiked": false
},
"summary": "Network with 4,000+ from the tech community, including folks from DFJ, Google, LinkedIn, Square, Uber, Y Combinator, 500 Startups, etc. $10 ticket gets you all-you-can-ride access to the pop-up Tech Carnival, will be the biggest Wednesday night of the tech summer.",
"title": "Tech Event @ Candlestick Park on Wednesday, July 17th! Come play carnival games with ~4,000 of the Bay area's best and brightest!"
},
{
"attachment": {
"contentDomain": "lifebeyondnumbers.com",
"contentUrl": "http://bit.ly/10VTqMu",
"imageUrl": "http://lifebeyondnumbers.com/wp-content/uploads/2013/07/lurnq_Online_Courses.jpg",
"summary": "LurnQ offers a platform for learning and teaching that is free for everyone. It caters to a diverse online audience and is relevant to everyone in general. The key segment that we address now is of life long learners.",
"title": "LurnQ - making lifelong learning clutter free, fun and a social..."
},
"comments": {
"_total": 0
},
"creationTimestamp": 1373883177000,
"creator": {
"firstName": "Syed",
"headline": "Founder and CEO at QubiqSquare",
"lastName": "Muksit",
"pictureUrl": "http://m.c.lnkd.licdn.com/mpr/mprx/0_Y5gdzlRCbQBTqIa-pXYnz-01b6KinDO-pFWnz-ZCZLk1WWdt-_SLUt2uWmrpzo0OxQxcVv6pRjbE"
},
"likes": {
"_total": 0
},
"relationToViewer": {
"availableActions": {
"_total": 7,
"values": [
{
"code": "add-comment"
},
{
"code": "categorize-as-job"
},
{
"code": "categorize-as-promotion"
},
{
"code": "flag-as-inappropriate"
},
{
"code": "follow"
},
{
"code": "like"
},
{
"code": "reply-privately"
}
]
},
"isFollowing": false,
"isLiked": false
},
"summary": "LurnQ offers a platform for learning and teaching that is free for everyone. It caters to a diverse online audience and is relevant to everyone in general. The key segment that we address now is of life long learners.",
"title": "There is so much to learn and most of the times, we don\u2019t even know that this-and-that good stuff exists. http://bit.ly/10VTqMu"
},
{
"attachment": {
"contentDomain": "techcarnival2013.eventbrite.com",
"contentUrl": "http://techcarnival2013.eventbrite.com/",
"imageUrl": "http://ebmedia.eventbrite.com/s3-s3/static/images/django/logos/eb_home_tm-trans-fb.png",
"summary": "Get to know a few thousand of Silicon Valley's best and brightest while enjoying unparalleled access to Candlestick Park,\u00a0games, food, music and more. We'll have carnival games you haven't played since you were ten, giant inflatable obstacle...",
"title": "Tech Carnival @ Candlestick Park"
},
"comments": {
"_total": 0
},
"creationTimestamp": 1373654758000,
"creator": {
"firstName": "Clayton",
"headline": "Director of Operations",
"lastName": "K.",
"pictureUrl": "http://m.c.lnkd.licdn.com/mpr/mprx/0_R7Vm6_RqBDHaHCDzJHRA6hsNcwOfECjzMeaA6heqHeo0v6ovBWoCe8pVJiYrd5pJVu4KdbnQQ3Lj"
},
"likes": {
"_total": 0
},
"relationToViewer": {
"availableActions": {
"_total": 7,
"values": [
{
"code": "add-comment"
},
{
"code": "categorize-as-job"
},
{
"code": "categorize-as-promotion"
},
{
"code": "flag-as-inappropriate"
},
{
"code": "follow"
},
{
"code": "like"
},
{
"code": "reply-privately"
}
]
},
"isFollowing": false,
"isLiked": false
},
"summary": "Network with 4,000+ from the tech community, including folks from DFJ, Google, LinkedIn, Square, Uber, Y Combinator, 500 Startups, etc. $10 ticket gets you all-you-can-ride access to the pop-up Tech Carnival, will be the biggest Wednesday night of the tech summer.",
"title": "Tech Event @ Candlestick Park on Wednesday, July 17th! Come play carnival games with ~4,000 of the Bay area's best and brightest!"
}
..........
........ so on
]
so im in a confusion how to read the json object in my custom inputformat class.any ideas on how to parse this?i want to read individual json object inside the json array,i mean read the proper json string and then give the string to map where i would use a json parser inside the map to construct my own key value pair.any help on this?thanks in advance
If your questions is in accordance with what Magham Ravi commented, the answer is fine.
But, if you have a single file with all JSON data as you have mentioned above, you might want to read the whole file and retrieve it as a String from the value part (BytesWritable value) in map function and feed it to your JSON parser available inside the same map() function.
Please have a look at WholeFileInputFormat
Furthermore, if you have say multiple JSON object data in a single file and what to get each JSON object data as values in the mapper, you can use something like the XMLInputFormat with start and end tags defined. In your case for JSON, you must have a unique start and end tags that exactly marks the start and end of a single JSON data object you want. Merely, using start-tag = "[{" and end-tag = "}]" might not help if you want the whole JSON object as above to be returned as a value, because you already have many of those nested that would confuse the InputFormat.
If you are not able to achieve the above in any case, try building your customTextInputFormat overriding LineReader defined in TextInputFormat.
In LineReader class, you'll fine these two set ( I may be a little outdated, please check if that's configurable now using a configuration property, I know that CDH has made it configurable, if not your need to override)
private static final byte CR = '\r';
private static final byte LF = '\n';
And you can let go CR and change LF to poing to "]\n[", since each of your independent JSON data would be in the form as shown or you'll know it better how?
[
...JSON 1
]
[
...JSON 2
]
[
...JSON N
]
(NOTE: There is a \n in between ] and [ that marks as a boundary between different JSON object's data.
Hope this makes sense.
来源：https://stackoverflow.com/questions/18593595/custom-inputformat-for-reading-json-in-hadoop