A better way of code generator in Java?

Question

I have a class with a graph inside. I iterate the graph and create a string that builds the graph, and then I just write that string into a Java file. Is there a better way of doing this, i read about JDT and CodeModel but I really am needing some hint of how to get used with it.

EDIT

I am doing a regular expression code generator, so far I have converted the Regular Expression into a DFA represented in a directedgraph (using grail library). When I have the DFA the next step is to generate a class that have three methods, 1st one builds the same graph (DFA), 2nd method moves from one node to another, and the third method matches if the input string is accepted one. Only first method is changing depending on the regularexpression input, the other two are static and same for each generated java class.

My string based approach looks like:

 import grail.interfaces.DirectedEdgeInterface;
 import grail.interfaces.DirectedGraphInterface;
 import grail.interfaces.DirectedNodeInterface;
 import grail.interfaces.EdgeInterface;
 import grail.iterators.EdgeIterator;
 import grail.iterators.NodeIterator;
 import grail.properties.GraphProperties;
 import grail.setbased.SetBasedDirectedGraph;

 public class ClassName {

private SetBasedDirectedGraph graph = new SetBasedDirectedGraph();
private static DirectedNodeInterface state;
private static DirectedNodeInterface currentState;
protected DirectedEdgeInterface edge;

public ClassName() {
    buildGraph();
}

protected void buildGraph() {

    // Creating Graph Nodes (Automaton States)

    state = graph.createNode(3);
    state.setProperty(GraphProperties.LABEL, "3");
    state.setProperty(GraphProperties.DESCRIPTION, "null");
    graph.addNode(state);
    state = graph.createNode(2);
    state.setProperty(GraphProperties.LABEL, "2");
    state.setProperty(GraphProperties.DESCRIPTION, "null");
    graph.addNode(state);
    state = graph.createNode(1);
    state.setProperty(GraphProperties.LABEL, "1");
    state.setProperty(GraphProperties.DESCRIPTION, "Accepted");
    graph.addNode(state);
    state = graph.createNode(0);
    state.setProperty(GraphProperties.LABEL, "0");
    state.setProperty(GraphProperties.DESCRIPTION, "Initial");
    graph.addNode(state);
            .....


    // Creating Graph Edges (Automaton Transitions)

    edge = graph.createEdge(null, (DirectedNodeInterface) graph.getNode(2),
            (DirectedNodeInterface) graph.getNode(1));
    edge.setProperty((GraphProperties.LABEL), "0");
    graph.addEdge(edge);
    edge = graph.createEdge(null, (DirectedNodeInterface) graph.getNode(2),
            (DirectedNodeInterface) graph.getNode(2));
    edge.setProperty((GraphProperties.LABEL), "1");
    graph.addEdge(edge);
    edge = graph.createEdge(null, (DirectedNodeInterface) graph.getNode(1),
            (DirectedNodeInterface) graph.getNode(1));
    edge.setProperty((GraphProperties.LABEL), "0");
    graph.addEdge(edge);
    edge = graph.createEdge(null, (DirectedNodeInterface) graph.getNode(1),
            (DirectedNodeInterface) graph.getNode(3));
    edge.setProperty((GraphProperties.LABEL), "1");
    graph.addEdge(edge);
    edge = graph.createEdge(null, (DirectedNodeInterface) graph.getNode(0),
            (DirectedNodeInterface) graph.getNode(1));
    edge.setProperty((GraphProperties.LABEL), "0");
    graph.addEdge(edge);
    edge = graph.createEdge(null, (DirectedNodeInterface) graph.getNode(0),
            (DirectedNodeInterface) graph.getNode(2));
    edge.setProperty((GraphProperties.LABEL), "1");
    graph.addEdge(edge);
}
}  

Answer 1

Another solution would be to stick to the current technology but provide a small layer with the builder pattern. To implement the builder you need a small one time effort, but get much better readable code.

I implemented the first part of your code. With the proper builder you could write:

graph = new GraphBuilder()
    .createNode(3).setLabel("3").setDescription("null").add()
    .createNode(2).setLabel("2").setDescription("null").add()
    .createNode(1).setLabel("1").setDescription("Accepted").add()
    .createNode(0).setLabel("0").setDescription("Initial").add()
    // unimplemented start
    .createEdge(2, 1).setLabel("0").add()
    .createEdge(2, 2).setLabel("1").add()
    .createEdge(1, 1).setLabel("0").add()
    .createEdge(1, 3).setLabel("1").add()
    .createEdge(0, 1).setLabel("0").add()
    .createEdge(0, 2).setLabel("1").add()
    // unimplemented end
    .build();

Much more readable, isn't it? To get this you need two builders. First comes the GraphBuilder:

package at.corba.test.builder;

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Builder for generating graphs.
 * @author ChrLipp
 */
public class GraphBuilder {
    /** List of StateBuilder, accesable via nodeNumber. */
    Map<Integer, StateBuilder> stateBuilderMap = new LinkedHashMap<Integer, StateBuilder>();

    /**
     * Delegates node-specific building to NodeBuilder.
     * @param nodeNumber Number of node to create
     * @return NodeBuilder for the node instance to create.
     */
    public StateBuilder createNode(final int nodeNumber) {
        StateBuilder builder = new StateBuilder(this);
        stateBuilderMap.put(nodeNumber, builder);
        return  builder;
    }

    /**
     * Builder function to initialise the graph.
     */
    public SetBasedDirectedGraph build() {
        SetBasedDirectedGraph graph = new SetBasedDirectedGraph();

        for (int key : stateBuilderMap.keySet()) {
            StateBuilder builder = stateBuilderMap.get(key);
            State state = graph.createNode(key);
            state = builder.build(state);
            graph.addNode(state);
        }

        return graph;
    }
}

and than the StateBuilder:

package at.corba.test.builder;

import java.util.HashMap;
import java.util.Map;

/**
 * Builder for generating states.
 * @author ChrLipp
 */
public class StateBuilder {
    /** Parent builder */
    private final GraphBuilder graphBuilder;

    /** Properties for this node */
    Map<GraphProperties, String> propertyMap = new HashMap<GraphProperties, String>();

    /**
     * ctor.
     * @param graphBuilder  Link to parent builder
     * @param nodeNumber    Node to create
     */
    public StateBuilder(final GraphBuilder graphBuilder)  {
        this.graphBuilder = graphBuilder;
    }

    /**
     * Property setter for property Label.
     * @param label value for property label
     * @return current NodeBuilder instance for method chaining
     */
    public StateBuilder setLabel(final String label) {
        propertyMap.put(GraphProperties.LABEL, label);
        return this;
    }

    /**
     * Property setter for description Label.
     * @param description value for description label
     * @return current NodeBuilder instance for method chaining
     */
    public StateBuilder setDescription(final String description) {
        propertyMap.put(GraphProperties.DESCRIPTION, description);
        return this;
    }

    /**
     * DSL function to close the node section and to return control to the parent builder.
     * @return
     */
    public GraphBuilder add() {
        return graphBuilder;
    }

    /**
     * Builder function to initialise the node.
     * @return newly generated node
     */
    public State build(final State state) {
        for (GraphProperties key : propertyMap.keySet()) {
            String value = propertyMap.get(key);
            state.setProperty(key, value);
        }

        return state;
    }
}

You would do the same for edges, but I did not implement this :-) . In Groovy it is even more easier to create builders (my implementation is a builder written in Java), see for example Make a builder.

Answer 2

A very simple example is given on the following blog :

http://namanmehta.blogspot.in/2010/01/use-codemodel-to-generate-java-source.html

You might want to have a look at it.

The problem with jcodemodel is that it is internally used by popular code generators like JAX-B and is not well documented. It also don't have any tutorials. But if you want to use this library, you can have a look at different blogs where the users have documented their experience / problem description and resolution .

Best of luck