Guava小结之 转变对象的强悍功能

   在之前的博文中介绍了guava强大的filter和transform，能转变各类东西，下面继续深入学习下，废话少说：

1） 将string转换为enum:
  
在guava 16中，可以将string转换为enum,

   

public enum Day {

    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
    THURSDAY, FRIDAY, SATURDAY;   
}

   其中可以使用stringConverter的方法，

@Test
public void transform_string_to_enum () {
    
    List<String> days = Lists.newArrayList(
            "WEDNESDAY", 
            "SUNDAY", 
            "MONDAY", 
            "WEDNESDAY");
    
    Function<String, Day> stringToDayEnum = Enums.stringConverter(Day.class);
    
    Iterable<Day> daysAsEnum = Iterables.transform(days, stringToDayEnum);
    
    for (Day day : daysAsEnum) {
        System.out.println(day);
    }
}

2  第2个应用场景，就是可以对一些对象进行转换，比如从一个对象转换到另外一个对象，如假设有两个对象：

  

public class ETradeInvestment {
    
    private String key;
    private String name;
    private BigDecimal price;

    ...
}

public class TdAmeritradeInvestment {
    
    private int investmentKey;
    private String investmentName;
    private double investmentPrice;

    ...
}

  

@Test
public void convert_tdinvestment_etradeinvestment () {
    
    List<TdAmeritradeInvestment> tdInvestments = Lists.newArrayList();
    tdInvestments.add(new TdAmeritradeInvestment(555, "Facebook Inc", 57.51));
    tdInvestments.add(new TdAmeritradeInvestment(123, "Micron Technology, Inc.", 21.29));
    tdInvestments.add(new TdAmeritradeInvestment(456, "Ford Motor Company", 15.31));
    tdInvestments.add(new TdAmeritradeInvestment(236, "Sirius XM Holdings Inc", 3.60));
    
   
    Function<TdAmeritradeInvestment, ETradeInvestment> tdToEtradeFunction = new Function<TdAmeritradeInvestment, ETradeInvestment>() {

        public ETradeInvestment apply(TdAmeritradeInvestment input) {
            ETradeInvestment investment = new ETradeInvestment();
            investment.setKey(Ints.stringConverter().reverse()
                    .convert(input.getInvestmentKey()));
            investment.setName(input.getInvestmentName());
            investment.setPrice(new BigDecimal(input.getInvestmentPrice()));
            return investment;
        }
    };

    List<ETradeInvestment> etradeInvestments = Lists.transform(tdInvestments, tdToEtradeFunction);
    
    System.out.println(etradeInvestments);
}

  可以看到，假如要把数据库中获得的记录中的LIST中的各个对象，一次过进行变换复制，更改其中某些值的话，用这个方法就最好了；
  如转换一个对象，容易办：

ETradeInvestment faceBookInvestment = tdToEtradeFunction
                .apply(new TdAmeritradeInvestment(555, "Facebook Inc", 57.51));

3  把list转为MAP，其中要用到guava中map的工具类了

@Test
public void transform_list_to_map () {
    
    List<TdAmeritradeInvestment> tdInvestments = Lists.newArrayList();
    tdInvestments.add(new TdAmeritradeInvestment(555, "Facebook Inc", 57.51));
    tdInvestments.add(new TdAmeritradeInvestment(123, "Micron Technology, Inc.", 21.29));
    tdInvestments.add(new TdAmeritradeInvestment(456, "Ford Motor Company", 15.31));
    tdInvestments.add(new TdAmeritradeInvestment(236, "Sirius XM Holdings Inc", 3.60));
    
    ImmutableMap<Integer, TdAmeritradeInvestment> investmentMap = Maps
            .uniqueIndex(tdInvestments,
                    new Function<TdAmeritradeInvestment, Integer>() {

                        public Integer apply(TdAmeritradeInvestment input) {
                            return new Integer(input.getInvestmentKey());
                        }
                    });
    
    System.out.println(investmentMap);
    
}