To create a new builder like a the MarkupBuilder or AntBuilder, you have to implement in java (in groovy later too) a subclass of the groovy.util.BuilderSupport class.
The main methods to be implemnted are the following :
package groovy.util; import groovy.lang.Closure; import groovy.lang.GroovyObjectSupport; import java.util.List; import java.util.Map; import org.codehaus.groovy.runtime.InvokerHelper; public abstract class BuilderSupport extends GroovyObjectSupport { private Object current; private Closure nameMappingClosure; private BuilderSupport proxyBuilder; public BuilderSupport() { this.proxyBuilder = this; } public BuilderSupport(BuilderSupport proxyBuilder) { this(null, proxyBuilder); } public BuilderSupport(Closure nameMappingClosure, BuilderSupport proxyBuilder) { this.nameMappingClosure = nameMappingClosure; this.proxyBuilder = proxyBuilder; } public Object invokeMethod(String methodName, Object args) { Object name = getName(methodName); return doInvokeMethod(methodName, name, args); } protected Object doInvokeMethod(String methodName, Object name, Object args) { Object node = null; Closure closure = null; List list = InvokerHelper.asList(args); //System.out.println("Called invokeMethod with name: " + name + " arguments: " + list); switch (list.size()) { case 0: break; case 1: { Object object = list.get(0); if (object instanceof Map) { node = proxyBuilder.createNode(name, (Map) object); } else if (object instanceof Closure) { closure = (Closure) object; node = proxyBuilder.createNode(name); } else { node = proxyBuilder.createNode(name, object); } } break; case 2: { Object object1 = list.get(0); Object object2 = list.get(1); if (object1 instanceof Map) { if (object2 instanceof Closure) { closure = (Closure) object2; node = proxyBuilder.createNode(name, (Map) object1); } else { node = proxyBuilder.createNode(name, (Map) object1, object2); } } else { if (object2 instanceof Closure) { closure = (Closure) object2; node = proxyBuilder.createNode(name, object1); } } } break; case 3: { Object attributes = list.get(0); Object value = list.get(1); closure = (Closure) list.get(2); node = proxyBuilder.createNode(name, (Map) attributes, value); } break; } if (node == null) { node = proxyBuilder.createNode(name); } if (current != null) { proxyBuilder.setParent(current, node); } if (closure != null) { // push new node on stack Object oldCurrent = current; current = node; // lets register the builder as the delegate setClosureDelegate(closure, node); closure.call(); current = oldCurrent; } proxyBuilder.nodeCompleted(current, node); return node; } protected void setClosureDelegate(Closure closure, Object node) { closure.setDelegate(this); } protected abstract void setParent(Object parent, Object child); protected abstract Object createNode(Object name); protected abstract Object createNode(Object name, Object value); protected abstract Object createNode(Object name, Map attributes); protected abstract Object createNode(Object name, Map attributes, Object value); protected Object getName(String methodName) { if (nameMappingClosure != null) { return nameMappingClosure.call(methodName); } return methodName; } protected void nodeCompleted(Object parent, Object node) { } protected Object getCurrent() { return current; } protected void setCurrent(Object current) { this.current = current; } }
To wbe able to write such a code :
someBuilder = new NodeBuilder() someBuilder.people(kind:'folks', groovy:true) { person(x:123, name:'James', cheese:'edam') { project(name:'groovy') project(name:'geronimo') } person(x:234, name:'bob', cheese:'cheddar') { project(name:'groovy') project(name:'drools') } }
we need :
package groovy.util; import java.util.ArrayList; import java.util.Map; /** * A helper class for creating nested trees of Node objects for * handling arbitrary data * * @author <a href="mailto:james@coredevelopers.net">James Strachan</a> * @version $Revision: 1.3 $ */ public class NodeBuilder extends BuilderSupport { public static NodeBuilder newInstance() { return new NodeBuilder(); } protected void setParent(Object parent, Object child) { } protected Object createNode(Object name) { return new Node(getCurrentNode(), name, new ArrayList()); } protected Object createNode(Object name, Object value) { return new Node(getCurrentNode(), name, value); } protected Object createNode(Object name, Map attributes) { return new Node(getCurrentNode(), name, attributes, new ArrayList()); } protected Object createNode(Object name, Map attributes, Object value) { return new Node(getCurrentNode(), name, attributes, value); } protected Node getCurrentNode() { return (Node) getCurrent(); } }
package groovy.xml; import groovy.util.BuilderSupport; import groovy.util.IndentPrinter; import java.io.PrintWriter; import java.io.Writer; import java.util.Iterator; import java.util.Map; /** * A helper class for creating XML or HTML markup * * @author <a href="mailto:james@coredevelopers.net">James Strachan</a> * @author Stefan Matthias Aust * @version $Revision: 1.8 $ */ public class MarkupBuilder extends BuilderSupport { private IndentPrinter out; private boolean nospace; private int state; private boolean nodeIsEmpty = true; public MarkupBuilder() { this(new IndentPrinter()); } public MarkupBuilder(PrintWriter writer) { this(new IndentPrinter(writer)); } public MarkupBuilder(Writer writer) { this(new IndentPrinter(new PrintWriter(writer))); } public MarkupBuilder(IndentPrinter out) { this.out = out; } protected void setParent(Object parent, Object child) { } /* public Object getProperty(String property) { if (property.equals("_")) { nospace = true; return null; } else { Object node = createNode(property); nodeCompleted(getCurrent(), node); return node; } } */ protected Object createNode(Object name) { toState(1, name); return name; } protected Object createNode(Object name, Object value) { toState(2, name); out.print(">"); out.print(value.toString()); return name; } protected Object createNode(Object name, Map attributes, Object value) { toState(1, name); for (Iterator iter = attributes.entrySet().iterator(); iter.hasNext();) { Map.Entry entry = (Map.Entry) iter.next(); out.print(" "); print(transformName(entry.getKey().toString())); out.print("='"); print(transformValue(entry.getValue().toString())); out.print("'"); } if (value != null) { nodeIsEmpty = false; out.print(">" + value + "</" + name + ">"); } return name; } protected Object createNode(Object name, Map attributes) { return createNode(name, attributes, null); } protected void nodeCompleted(Object parent, Object node) { toState(3, node); out.flush(); } protected void print(Object node) { out.print(node == null ? "null" : node.toString()); } protected Object getName(String methodName) { return super.getName(transformName(methodName)); } protected String transformName(String name) { if (name.startsWith("_")) name = name.substring(1); return name.replace('_', '-'); } protected String transformValue(String value) { return value.replaceAll("\\'", """); } private void toState(int next, Object name) { switch (state) { case 0: switch (next) { case 1: case 2: out.print("<"); print(name); break; case 3: throw new Error(); } break; case 1: switch (next) { case 1: case 2: out.print(">"); if (nospace) { nospace = false; } else { out.println(); out.incrementIndent(); out.printIndent(); } out.print("<"); print(name); break; case 3: if (nodeIsEmpty) { out.print(" />"); } break; } break; case 2: switch (next) { case 1: case 2: throw new Error(); case 3: out.print("</"); print(name); out.print(">"); break; } break; case 3: switch (next) { case 1: case 2: if (nospace) { nospace = false; } else { out.println(); out.printIndent(); } out.print("<"); print(name); break; case 3: if (nospace) { nospace = false; } else { out.println(); out.decrementIndent(); out.printIndent(); } out.print("</"); print(name); out.print(">"); break; } break; } state = next; } }