code: public void setOutputBinding(Map<String,String> value) {
  		outputBinding.clear();
  		outputBindingDefinitions.clear();
  		for (Map.Entry<String,String> entry : value.entrySet())
  			putOutputBinding(entry.getKey(), entry.getValue());
  	}
  
  	/**
  	 * Registers an expression for a field.
  	 * @param field the name.
  	 * @param expression the SpEL definition.
  	 */
  	public void putOutputBinding(String field, String expression) {
  		outputBindingDefinitions.put(field, expression);
  	}
  
  	private Expression getOutputBinding(String field) {
  		Expression binding = outputBinding.get(field);
  		if (binding == null) {
  			String definition = outputBindingDefinitions.get(field);
  			if (definition == null) {
  				if (outputFields.length == 1 && outputFields[0].equals(field))
  					definition = "#root";
  				else
  					definition = "#root?." + field;
  			}
  			logger.debug("Field {} bound as #{{}}", field, definition);
  			binding = expressionParser.parseExpression(definition);
  			outputBinding.put(field, binding);
  		}
  		return binding;
  	}
  
  	/**
  	 * Gets whether items in collection and array returns
  	 * should be emitted as individual output tuples.
  	 */
  	public boolean getScatterOutput() {
  		return scatterOutput;
  	}
  
  	/**
  	 * Sets whether items in collection and array returns
  	 * should be emitted as individual output tuples.
  	 */
  	public void setScatterOutput(boolean value) {
  		scatterOutput = value;
  	}
  
  	@Override
  	public Number getParallelism() {
  		return parallelism;
  	}
  
  	/**
  	 * Sets the Storm parallelism hint.
  	 */
  	public void setParallelism(Number value) {
  		parallelism = value;
  	}
  
  	@Override
  	public String getId() {
  		return id;
  	}
  
  	@Override
  	public void setId(String value) {
  		id = value;
  	}
  
  	@Override
  	public void setApplicationContext(ApplicationContext value) {
  		spring = value;
  	}
docs: Sets expressions per field.
  @see #putOutputBinding(String, String)