通用JSF实体转换器 [英] Generic JSF entity converter

问题描述

我正在编写我的第一个Java EE 6 Web应用程序作为学习练习。我没有使用框架，只有JPA 2.0，EJB 3.1和JSF 2.0。

I'm writing my first Java EE 6 web app as a learning exercise. I'm not using a framework, just JPA 2.0, EJB 3.1 and JSF 2.0.

我有一个自定义转换器，用于将存储在SelectOne组件中的JPA实体转换回实体。我正在使用InitialContext.lookup来获取对会话Bean的引用以查找相关的实体。

I have a Custom Converter to convert a JPA Entity stored in a SelectOne component back to an Entity. I'm using an InitialContext.lookup to obtain a reference to a Session Bean to find the relevant Entity.

我想创建一个通用的实体转换器，所以我不必为每个实体创建一个转换器。我以为我会创建一个抽象实体并让所有实体扩展它。然后为抽象实体创建自定义转换器，并将其用作所有实体的转换器。

I'd like to create a generic Entity Converter so I don't have to create a converter per Entity. I thought I'd create an Abstract Entity and have all Entities extend it. Then create a Custom Converter for the Abstract Entity and use it as the converter for all Entities.

这听起来合理和/或切实可行吗？

Does that sound sensible and/or practicable?

没有一个抽象的实体，只是转换器可以转换任何实体更有意义吗？在那种情况下，我不确定如何获得对相应会话Bean的引用。

Would it make more sense not to have an abstract entity, just a converter that converts any entity? In that case I'm not sure how I'd obtain a reference to the appropriate Session Bean.

我已经包含了我当前的转换器因为我不确定我以最有效的方式获取对Session Bean的引用。

I've included my current converter because I'm not sure I'm obtaining a reference to my Session Bean in the most efficient manner.

package com.mycom.rentalstore.converters;

import com.mycom.rentalstore.ejbs.ClassificationEJB;
import com.mycom.rentalstore.entities.Classification;
import javax.faces.application.FacesMessage;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
import javax.faces.convert.ConverterException;
import javax.faces.convert.FacesConverter;
import javax.naming.InitialContext;
import javax.naming.NamingException;

@FacesConverter(forClass = Classification.class)
public class ClassificationConverter implements Converter {

    private InitialContext ic;
    private ClassificationEJB classificationEJB;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {

        try {
            ic = new InitialContext();
            classificationEJB = (ClassificationEJB) ic.lookup("java:global/com.mycom.rentalstore_RentalStore_war_1.0-SNAPSHOT/ClassificationEJB");

        } catch (NamingException e) {
            throw new ConverterException(new FacesMessage(String.format("Cannot obtain InitialContext - %s", e)), e);
        }

        try {
            return classificationEJB.getClassificationById(Long.valueOf(value));
        } catch (Exception e) {
            throw new ConverterException(new FacesMessage(String.format("Cannot convert %s to Classification - %s", value, e)), e);
        }
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        return String.valueOf(((Classification) value).getId());
    }
}

推荐答案

好我今天遇到了同样的问题，我通过创建一个通用的ConversionHelper并在转换器中使用它来解决它。
为此，我有一个EntityService，它是一个通用的SLSB，我用它来为任何实体类型执行简单的CRUD操作。我的实体也实现了一个PersistentEntity接口，它有一个getId和setId方法，我用简单的主键保存它们。就是这样。

Well I had the same problem today, and I solved it by creating a generic ConversionHelper and using it in the converter. For this purpose I have an EntityService which is a generic SLSB that I use to perform simple CRUD operations for any entity type. Also my entities implement a PersistentEntity interface, which has a getId and setId methods and I keep them with simple primary keys. That's it.

最后我的转换器看起来像这样：

In the end my converter looks like this:

@FacesConverter(value = "userConverter", forClass = User.class)
public class UserConverter implements Converter {

    @Override
    public Object getAsObject(FacesContext ctx, UIComponent component, java.lang.String value) {

        return ConversionHelper.getAsObject(User.class, value);
    }

    @Override
    public String getAsString(FacesContext ctx, UIComponent component, Object value) {

        return ConversionHelper.getAsString(value);
    }
}

我的转换助手看起来像这样：

And my conversion helper looks like this:

public final class ConversionHelper {

    private ConversionHelper() {
    }

    public static <T> T getAsObject(Class<T> returnType, String value) {

        if (returnType== null) {

            throw new NullPointerException("Trying to getAsObject with a null return type.");
        }

        if (value == null) {

            throw new NullPointerException("Trying to getAsObject with a null value.");
        }

        Long id = null;

        try {

            id = Long.parseLong(value);

        } catch (NumberFormatException e) {

            throw new ConverterException("Trying to getAsObject with a wrong id format.");
        }

        try {

            Context initialContext = new InitialContext();
            EntityService entityService = (EntityService) initialContext.lookup("java:global/myapp/EntityService");

            T result = (T) entityService.find(returnType, id);

            return result;

        } catch (NamingException e) {

            throw new ConverterException("EntityService not found.");
        }
    }

    public static String getAsString(Object value) {

        if (value instanceof PersistentEntity) {

            PersistentEntity result = (PersistentEntity) value;

            return String.valueOf(result.getId());
        }

        return null;
    }
}

现在为简单的JPA实体创建转换器是一个重复的转换器并更改3个参数。

Now creating converters for simple JPA entities is a matter of duplicate a converter and change 3 parameters.

这对我来说效果很好，但我不知道它是否是风格方面的最佳方法和表现。任何提示将不胜感激。

This is working well for me, but I don't know if it is the best approach in terms of style and performance. Any tips would be appreciated.

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