Processing json data with apache velocity.

I've written a tool named "apache velocity" which parse json data and processes it with "Apache velocity" (a template engine ). The (javacc) source code is available here:

https://github.com/lindenb/jsandbox/blob/master/src/sandbox/VelocityJson.jj

Example

Say you have defined some classes using JSON:

[
  {
    "type": "record",
    "name": "Exon",
    "fields" : [
      {"name": "start", "type": "int"},
      {"name": "end", "type": "int"}
    ]
  },
  {
    "type": "record",
    "name": "Gene",
    "fields" : [
      {"name": "chrom", "type": "string"},
      {"name": "name", "type": "string"},
      {"name": "txStart", "type": "int"},
      {"name": "txEnd", "type": "int"},
      {"name": "cdsStart", "type": "int"},
      {"name": "cdsEnd", "type": "int"},
      {"name": "exons", "type":{"type":"array","items":"Exon"}}
    ]
  } 
 ]

and here is a velocity template transforming this json structure to java :

#macro(javaName $s)$s.substring(0,1).toUpperCase()$s.substring(1)#end
#macro(setter $s)set#javaName($s)#end
#macro(getter $s)get#javaName($s)#end
#macro(javaType $f)
#if($f.type.equals("string"))
java.lang.String#elseif($f.type.equals("boolean"))
boolean#elseif($f.type.equals("long"))
long#elseif($f.type.equals("float"))
float#elseif($f.type.equals("double"))
double#elseif($f.type.equals("int"))
int#elseif($f.items)
$f.items#elseif($f.type.type.equals("array"))
java.util.List<#javaType($f.type)>#else
$f.type
#end
#end

#foreach( $class in $avro)

class $class.name
{
#foreach( $field in $class.fields )
private  #javaType($field) $field.name;
#end

public ${class.name}()
 {
 }

public ${class.name}(#foreach( $field in $class.fields )
 #if($velocityCount>1),#end#javaType($field) $field.name
 #end
 )
 {
 #foreach( $field in $class.fields )
 this.$field.name=$field.name;
 #end
 }
 


#foreach( $field in $class.fields )
public void #setter($field.name)(#javaType($field) $field.name)
 {
 this.$field.name=$field.name;
 }
public #javaType($field) #getter($field.name)()
 {
 return this.$field.name;
 }
#end
}
#end

The json file can be processed with velocity using the following command line:

$ java -jar velocityjson.jar -f avro structure.json json2java.vm

Result

class Exon
{
private  int start;
private  int end;

public Exon()
 {
 }

public Exon( int start
  ,int end
  )
 {
  this.start=start;
  this.end=end;
  }
 


public void setStart(int start)
 {
 this.start=start;
 }
public int getStart()
 {
 return this.start;
 }
public void setEnd(int end)
 {
 this.end=end;
 }
public int getEnd()
 {
 return this.end;
 }
}

class Gene
{
private  java.lang.String chrom;
private  java.lang.String name;
private  int txStart;
private  int txEnd;
private  int cdsStart;
private  int cdsEnd;
private  java.util.List<Exon> exons;

public Gene()
 {
 }

public Gene( java.lang.String chrom
  ,java.lang.String name
  ,int txStart
  ,int txEnd
  ,int cdsStart
  ,int cdsEnd
  ,java.util.List<Exon> exons
  )
 {
  this.chrom=chrom;
  this.name=name;
  this.txStart=txStart;
  this.txEnd=txEnd;
  this.cdsStart=cdsStart;
  this.cdsEnd=cdsEnd;
  this.exons=exons;
  }
 


public void setChrom(java.lang.String chrom)
 {
 this.chrom=chrom;
 }
public java.lang.String getChrom()
 {
 return this.chrom;
 }
public void setName(java.lang.String name)
 {
 this.name=name;
 }
public java.lang.String getName()
 {
 return this.name;
 }
public void setTxStart(int txStart)
 {
 this.txStart=txStart;
 }
public int getTxStart()
 {
 return this.txStart;
 }
public void setTxEnd(int txEnd)
 {
 this.txEnd=txEnd;
 }
public int getTxEnd()
 {
 return this.txEnd;
 }
public void setCdsStart(int cdsStart)
 {
 this.cdsStart=cdsStart;
 }
public int getCdsStart()
 {
 return this.cdsStart;
 }
public void setCdsEnd(int cdsEnd)
 {
 this.cdsEnd=cdsEnd;
 }
public int getCdsEnd()
 {
 return this.cdsEnd;
 }
public void setExons(java.util.List<Exon> exons)
 {
 this.exons=exons;
 }
public java.util.List<Exon> getExons()
 {
 return this.exons;
 }
}

That's it,

Pierre