Editing a complex Java object in a Tapestry 5 web application

Question 1

I would suggest to build a thin wrapper around the Objects you would like to edit though the BeanEditForm and pass those into it. So something like:

public class TapestryProject {

   private Project project;

   public TapestryProject(Project proj){
      this.project = proj;
   }

   public String getName(){
      this.project.getProjectName().getValue();
   }

   public void setName(String name){
      this.project.getProjectName().setValue(name);
   }

   etc...
}

This way tapestry will deal with all the types it knows about leaving you free of having to create your own coersions (which is quite simple in itself by the way).

Question 2

You can contribute blocks to display and edit your "link" and "literal" datatypes.

The beaneditform, beaneditor and beandisplay are backed by the BeanBlockSource service. BeanBlockSource is responsible for providing display and edit blocks for various datatypes.

If you download the tapestry source code and have a look at the following files:

tapestry-core\src\main\java\org\apache\tapestry5\corelib\pages\PropertyEditBlocks.java
tapestry-core\src\main\resources\org\apache\tapestry5\corelib\pages\PropertyEditBlocks.tml
tapestry-core\src\main\java\org\apache\tapestry5\services\TapestryModule.java

You will see how tapestry contributes EditBlockContribution and DisplayBlockContribution to provide default blocks (eg for a "date" datatype).

If you contribute to BeanBlockSource, you could provide display and edit blocks for your custom datatypes. This will require you reference blocks by id in a page. The page can be hidden from your users by annotating it with @WhitelistAccessOnly.

Question 3

Here's an example of using an interface and a proxy to hide the implementation details from your model. Note how the proxy takes care of updating the modified flag and is able to map URI's from the Literal array to properties in the HumanBeing interface.

package com.github.uklance.triplestore;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

import org.junit.Test;

public class TripleStoreOrmTest {
    public static class Literal<T> {
        public String uri;
        public boolean modified;
        public Class<T> type;
        public T value;

        public Literal(String uri, Class<T> type, T value) {
            super();
            this.uri = uri;
            this.type = type;
            this.value = value;
        }

        @Override
        public String toString() {
            return "Literal [uri=" + uri + ", type=" + type + ", value=" + value + ", modified=" + modified + "]";
        }
    }

    public interface HumanBeing {
        public String getName();
        public void setName(String name);

        public int getAge();
        public void setAge();
    }

    public interface TripleStoreProxy {
        public Map<String, Literal<?>> getLiteralMap();
    }

    @Test
    public void testMockTripleStore() {
        Literal<?>[] literals = {
            new Literal<String>("http://humanBeing/1/Name", String.class, "Henry"),
            new Literal<Integer>("http://humanBeing/1/Age", Integer.class, 21)
        };

        System.out.println("Before " + Arrays.asList(literals));

        HumanBeing humanBeingProxy = createProxy(literals, HumanBeing.class);

        System.out.println("Before Name: " + humanBeingProxy.getName());
        System.out.println("Before Age: " + humanBeingProxy.getAge());

        humanBeingProxy.setName("Adam");

        System.out.println("After Name: " + humanBeingProxy.getName());
        System.out.println("After Age: " + humanBeingProxy.getAge());

        Map<String, Literal<?>> literalMap = ((TripleStoreProxy) humanBeingProxy).getLiteralMap();
        System.out.println("After " + literalMap);
    }

    protected <T> T createProxy(Literal<?>[] literals, Class<T> type) {
        Class<?>[] proxyInterfaces = { type, TripleStoreProxy.class };

        final Map<String, Literal> literalMap = new HashMap<String, Literal>();
        for (Literal<?> literal : literals) {
            String name = literal.uri.substring(literal.uri.lastIndexOf("/") + 1);
            literalMap.put(name,  literal);
        }

        InvocationHandler handler = new InvocationHandler() {
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                if (method.getDeclaringClass().equals(TripleStoreProxy.class)) {
                    return literalMap;
                }
                if (method.getName().startsWith("get")) {
                    String name = method.getName().substring(3);
                    return literalMap.get(name).value;
                } else if (method.getName().startsWith("set")) {
                    String name = method.getName().substring(3);
                    Literal<Object> literal = literalMap.get(name);
                    literal.value = args[0];
                    literal.modified = true;
                }    
                return null;
            }
        };

        return type.cast(Proxy.newProxyInstance(getClass().getClassLoader(), proxyInterfaces, handler));
    }
}