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如何在不使用getter方法的情况下获取对象的所有实例变量?

instance-variables reflection java

Adi Sembiring · 技术社区 · 15 年前

我有一节POJO课

Class Book {
private String id;
private String title;

Public Book() {
}

//implement setter and getter
..............

}

main() {
Book book = new Book();
book.setId(1);
book.setTitle("new moon");

}

我希望结果变成->1,“新月” 不使用getter方法,所以我可以转换另一个POJO对象。

澄清:

我有2节课

Book {
String id;
String title;

//constructor

//setter
}

Student {
    String id;
    String name;

    //cuonstructor

    //setter
}

main() {
Book book = new Book();
book.setId(1);
book.setTitle("new moon");

Student student = new Student();
student.setId(1);
student.setName("andrew");

//suppose i have BeanUtil object to get all instance varable value and class meta data
BeanUtil.getMetadata(book, Book.class);
//output is
//id, title

//suppose i have BeanUtil object to get all instance varable value and class meta data
BeanUtil.getMetadata(student, Students.class);
//output is
//id, name

BeanUtil.getInstanceVariableValue(student, Student.class);
//output
//1, andrew

BeanUtil.getInstanceVariableValue(book, Book.class);
//output
//1, new moon
}

6 回复 | 直到 13 年前

MattMcKnight 15 年前

我通常使用 PropertyUtils 它是 BeanUtils .

//get all of the properties for a POJO
descriptors = PropertyUtils.getPropertyDescriptors(book);
//go through all values
Object value = null;
for ( int i = 0; i < descriptors.length; i++ ) {
     value = PropertyUtils.getSimpleProperty(bean, descriptors[i].getName())
 }         
//copy properties from POJO to POJO
PropertyUtils.copyProperties(fromBook, toBook);

Stephen C 15 年前

如果您想获得一个Book实例的所有属性的值,可以使用反射来实现。然而,这将需要大量的代码,而且成本高昂。更好的方法是(IMO)简单地实现 getAllValues() 方法:

public Object[] getAllValues() {
    return new Object[]{this.id, this.title};
}

Droo 15 年前

听起来像是你项目的重点(我假设是一个家庭作业项目?)是为了学习 Reflections

martinatime 9 年前

这个怎么样:

public static String getMetadata(Class input) {
  StringBuffer result = new StringBuffer();
  // this will get all fields declared by the input class
  Field[] fields = input.getDeclaredFields();
  for (int i=0; i<fields.length; i++) {
    if (i > 0) {
      result.append(", ");
    }
    field[i].setAccessible(true);
    result.append(field[i].getName());
  }
}

public static String getInstanceVariableValue(Object input) {
  StringBuffer result = new StringBuffer();
  // this will get all fields declared by the input object
  Field[] fields = input.getClass().getDeclaredFields();
  for (int i=0; i<fields.length; i++) {
    if (i > 0) {
      result.append(", ");
    }
    fields[i].setAccessible(true);
    result.append(fields[i].get(input));
  }
    return result;
}

我没有试图编译或运行这个,所以让我知道它是如何进行的

Doug Paul aleemb 15 年前

像迈克尔一样,我不确定我是否完全理解你的问题。听起来您希望能够在给定包含其标题的字符串的情况下获取Book对象。假设您已如上所述声明了Book类,请尝试以下操作:

public class Book {
    private String id;
    private String title;

    public Book(String id, String title) {
        this.id = id;
        this.title = title;
    }

    // Setters and getters...

}

public class Library {
    private Map<String, Book> booksByTitle = new HashMap<String, Book>();

    public Library() {
    }

    public void addBook(Book book) {
        this.booksByTitle.put(book.getTitle(), book);
    }

    public Book getBookByTitle(String title) {
        // Returns null if no matching entry is found in the map.
        return this.booksByTitle.get(title);
    }

    public static void main(String args[]) {
        Library myLibrary = new Library();

        myLibrary.addBook(new Book("1", "new moon"));
        myLibrary.addBook(new Book("2", "fight club"));

        Book book = myLibrary.getBookByTitle("new moon");

        if (book == null) {
            // A book by that title is not in the library
        }
    }
}

martinatime 15 年前

我认为adisembiring要问的是如何在POJO中获取值,而不调用每个实例变量的单独getter。有一种方法可以使用反射来实现这一点。 Here