AWS API Gateway - Integration Response body mapping - amazon-web-services

Question

In AWS API Gateway Integration Response body mapping I have following code:
#set($inputRoot = $input.path('$.Item'))
[
#foreach($elem in $inputRoot.Events)
{
"id": $elem.id,
"from" : $elem.from,
"to" : $elem.to,
"spent" : $elem.spent,
#if("$!elem.comment" != "")
"comment": $elem.comment,
#end
"project" : {
"id" : $elem.project.id,
"number" : $elem.project.number,
"name" : $elem.project.name
}
}
#if($foreach.hasNext),#end
#end
]
The data comes from a lambda functions which queries a DynamoDB Table
API gateway returns the data like this:
[
{
"id": 123443214,
"from" : 19:34,
"to" : 22:30,
"spent" : 02:56,
"project" : {
"id" : 4321,
"number" : CIB,
"name" : Backend
}
}
, {
"id": 12341234,
"from" : 19:34,
"to" : 22:30,
"spent" : 02:56,
"project" : {
"id" : 12341234,
"number" : CIB,
"name" : Backend
}
}
]
So it it's already formatted. How do I get APi Gateway to return the response unformatted? So that it's just pure json, without break lines, indentations etc.?
Thanks in advance!

Answer 1

(Small preliminary remark: you are missing some quotes around JSON string values).
It's possible to remove line breaks using ## and indentation using #**#, as follow, but the template will look a bit ugly:
#set($inputRoot = $input.path('$.Item'))##
[##
#foreach($elem in $inputRoot.Events)##
{##
#**#"id":$elem.id,##
#**#"from": $elem.from,##
#**#"to":$elem.to,##
#**#"spent":$elem.spent,##
#if("$!elem.comment" != "")##
#* *#"comment":$elem.comment,##
#end##
#**#"project":{##
#**#"id":$elem.project.id,##
#**#"number":"$elem.project.number",##
#**#"name":"$elem.project.name"##
}##
}##
#if($foreach.hasNext),#end##
#end##
]##
Since the only reason the indentation is in here at first is readability of the template, I would go another direction.
For instance, you can add a post-processing tidy formatter in your View servlet) using org.json:
import org.json.JSONObject;
....
Writer writer = new StringWriter();
getVelocityView().merge(template, context, writer);
String compactJSON = new JSONObject(writer.toString()).toString();
response.getWriter().write(compactJSON);
But this will only work for small JSON files since the response is buffered into memory, so let's keep on searching for a more elegant solution.
The way to go is to pre-process your template, using a custom ResouceLoader.
CompactJSONResourceLoader.java
package my.custom.loader;
import java.io.InputStream;
import java.io.IOException;
import org.apache.commons.collections.ExtendedProperties;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.runtime.resource.Resource;
import org.apache.velocity.runtime.resource.loader.ResourceLoader;
import org.apache.velocity.runtime.resource.loader.ResourceLoaderFactory;
public class CompactJSONResourceLoader extends ResourceLoader
{
protected ResourceLoader innerLoader = null;
#Override
public void init(ExtendedProperties configuration)
{
try
{
String innerLoaderID = configuration.getString("innerLoader") + ".resource.loader";
String innerLoaderClass = rsvc.getConfiguration().getString(innerLoaderID + ".class");
innerLoader = ResourceLoaderFactory.getLoader(rsvc, innerLoaderClass);
ExtendedProperties innerConfiguration = rsvc.getConfiguration().subset(innerLoaderID);
innerLoader.commonInit(rsvc, innerConfiguration);
innerLoader.init(innerConfiguration);
}
catch (Exception e)
{
log.error("could not initialize CompactJSONResourceLoader inner loader", e);
}
}
protected class CompactJSONInputStream extends InputStream
{
InputStream innerStream = null;
boolean insideQuotes = false;
public CompactJSONInputStream(InputStream innerStream)
{
this.innerStream = innerStream;
}
#Override
public int read() throws IOException
{
int ch;
do
{
ch = innerStream.read();
if (insideQuotes)
{
if (ch == '"') insideQuotes = false;
break;
}
else if (!Character.isWhitespace(ch))
{
if (ch == '"') insideQuotes = true;
break;
}
}
while (ch != -1);
return ch;
}
}
#Override
public InputStream getResourceStream(String source) throws ResourceNotFoundException
{
return new CompactJSONInputStream(innerLoader.getResourceStream(source));
}
#Override
public boolean isSourceModified(Resource resource)
{
return innerLoader.isSourceModified(resource);
}
#Override
public long getLastModified(Resource resource)
{
return innerLoader.getLastModified(resource);
}
}
And you would then need to configure Velocity with the following properties:
resource.loader = compact
compact.resource.loader.class = my.custom.loader.CompactJSONResourceLoader
compact.resource.loader.innerLoader = file
(you would replace file with the resource loader you are currently using, of course).