# JSON Output
##  JSON Output
### Description
The JSON Output transform allows you to generate JSON blocks based on input transform values.
Output JSON will be available as a javascript array or a javascript object depending on the transform settings.
| Hop Engine | ✓ |
| ---------- | ------------ |
| Spark | ✓ |
| Flink | ✓ |
| Dataflow | ✓ |
### Options
#### General Tab
General tab allows to specify type of transform operation, output json structure, transform output file. This file will be used to dump all generated json.
**Settings Section**
| Option | Description |
| ------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Transform name | Name of the transform; this name has to be unique in a single pipeline. |
| Operation | Specify transform operation type. Currently available 3 types of operation:
- Output value - only pass output json as a transform output field, do not dump to output file
- Write to file - only write to fie, do not pass to output field
- Output value and write to file - dump to file and pass generated json as a transform output file
|
| Json block name | This value will be used as a name for json block. |
| Nr. rows in a block | Number of rows that are combined as one JSON Array.
Note: A new file will be generated for each block.
|
| Note | A new file will be generated for each block |
| Output value | Output field name |
| Compatibility mode | Mode to be backwards compatible, more information [here](#compatibility-mode) |
**Output File Section**
| Option | Description |
| ----------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Filename | full path to output file |
| Append | When checked new rows will be appended to the existing files |
| Create Parent folder | When checked the parent folders will be created when they do not exist, else the transform will fail if the folder does not exist |
| Do not open create at start | If not checked:
file (and in some cases parent folder) will be created/opened to write during pipeline initialization.
If checked:
file and parent folder will be created only after transform will get any first input data.
|
| Extension | Output file extension. Default value is 'json' |
| Encoding | Output file encoding |
| Pass output to servlet | Enable this option to return the data via a web service instead writing into a file. |
| Include date in filename? | If checked - output file name will contains File name value + current date. This may help to generate unique output files. |
| Include time in filename | If checked - output file name will contains file creation time. Same as for 'Include date in filename' option |
| Show filename(s) button | Can be useful to test full output file path |
| Add file to result filenames? | If checked - created output file path will be accessible form transform result |
#### Fields Tab
This tab is used to map input transform fields to output json values
| Option | Description |
| ------------ | ---------------------------------------------------------------------------------------------------------------------------- |
| Element name | Json element name as a key. For example "A":"B" - A is a element name, B is actual input value mapped for this Element name. |
| Fieldname | Input transform field name. Use 'Get Fields' button to discover available input fields |
### Compatibility mode
This part of the documentation will explain the differences when turning on compatibility mode. For all new development this mode is **not** recommended. Imagine we are generating a simple \ list with keynames "name" and "value" and there corresponding values.
We will be using following settings:
* Json block name = "data"
* Nr rows in block = 3
* Compatibility mode = NOT checked (and this is the default option)
This will output:
First file:
```highlight
{
"data" : [ {
"name" : "item 1",
"value" : "value 1"
}, {
"name" : "item 2",
"value" : "value 2"
}, {
"name" : "item 3",
"value" : "value 3"
} ]
}
```
Second file:
```highlight
{
"data" : [ {
"name" : "item 4",
"value" : "value 4"
} ]
}
```
If compatibility mode is enabled and the transform has the following settings:
* Json block name = "data"
* Nr rows in block = 3
* 'Compatibility mode' is checked
This will output:
First file:
```highlight
{
"data": [
{
"name": "item 1"
},
{
"value": "value 1"
},
{
"name": "item 2"
},
{
"value": "value 2"
},
{
"name": "item 3"
},
{
"value": "value 3"
}
]
}
```
Second file:
```highlight
{
"data": [
{
"name": "item 4"
},
{
"value": "value 4"
}
]
}
```
As you can see when turning compatibility mode on, each field will be handles as a separate object.
---
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