JAVA:将 String 转换为(动态已知的)原始类型以实例化(动态已知的)类

Question

我有一个使用文本文件(要求)的存储库类，这意味着我必须读取字符串并转换它们才能实例化对象。问题是我希望我的存储库类尽可能通用，以便使用它来操作不同的对象类型。

那么，有没有一种(更优雅的)方法可以在运行时动态地将字符串转换为它需要的任何字段(原始)类型，同时避免大量的具有大量 ifs/switches 的 try-catch 结构？

作为一个简短的简化版本，我希望 objectA.txt 只包含 objectA 的信息，对于 objectB.txt 也是如此，而我的存储库代码可以处理这两者:

Repository repoA = new Repository("objectA.txt", <list of Types for A>);输入A a=repoA.getOne();

Repository repoB = new Repository("objectB.txt", <List of Types for B>);输入B b=repoB.getOne();

我有什么:

public class FileRepository extends InMemoryRepository{
    private String fileName;
    private List<Class> types;

    public FileRepository(String fileName, List<Class> types) {
        //@param types 
        //     - list containing the Class to be instantiated followed by it's field types
        super();
        this.fileName = fileName;
        this.types=types;
        loadData();
    }

    private void loadData() {
        Path path = Paths.get(fileName);

        try {
            Files.lines(path).forEach(line -> {
                List<String> items = Arrays.asList(line.split(","));

                //create Class array for calling the correct constructor
                Class[] cls=new Class[types.size()-1];
                for (int i=1; i<types.size(); i++){
                    cls[i-1]=types.get(i);
                }

                Constructor constr=null;
                try {
                    //get the needed constructor
                    constr = types.get(0).getConstructor(cls);
                } catch (NoSuchMethodException e) {
                    //do something
                    e.printStackTrace();
                }
                //here is where the fun begins
                //@arg0 ... @argn are the primitives that need to be casted from string 
                //something like: 
                //*(type.get(1))* arg0=*(cast to types.get(1))* items.get(0);
                //*(type.get(2))* arg1=*(cast to types.get(2))* items.get(1);
                //...

                Object obj= (Object) constr.newInstance(@arg0 ... @argn);

            });
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

P.S.:我是一个JAVA新手，所以请尽可能简单的解释。

Answer 1

手头没有 IDE，所以我希望这是有意义的:

private static final Map<Class, Function<String, ?>> parsers = new HashMap<>();

static {
  parsers.put(Long.class, Long::parseLong);
  parsers.put(Integer.class, Integer::parseInt);
  parsers.put(String.class, String::toString);
  parsers.put(Double.class, Double::parseDouble);
  parsers.put(Float.class, Float::parseFloat);
  // add your own types here.
}

public <T> T parse(Class<T> klass, String value) {
  // add some null-handling logic here? and empty values.
  return (T)parsers.get(klass).apply(value);
}

然后当您需要为构造函数创建参数时:

parameters =
     IntStream
     .range(0, cls.size-1)
     .map(i -> (Object)parse(types.get(i), items.get(i)))
     .toArray(Object[]::new);