java 三种将list转换为map的方法详解
java三种将list转换为map的方法详解
在本文中，介绍三种将list转换为map的方法：
1）传统方法
假设有某个类如下
classMovie{
privateIntegerrank;
privateStringdescription;
publicMovie(Integerrank,Stringdescription){
super();
this.rank=rank;
this.description=description;
}
publicIntegergetRank(){
returnrank;
}
publicStringgetDescription(){
returndescription;
}
@Override
publicStringtoString(){
returnObjects.toStringHelper(this)
.add("rank",rank)
.add("description",description)
.toString();
}
}
使用传统的方法：
@Test
publicvoidconvert_list_to_map_with_java(){
List<Movie>movies=newArrayList<Movie>();
movies.add(newMovie(1,"TheShawshankRedemption"));
movies.add(newMovie(2,"TheGodfather"));
Map<Integer,Movie>mappedMovies=newHashMap<Integer,Movie>();
for(Moviemovie:movies){
mappedMovies.put(movie.getRank(),movie);
}
logger.info(mappedMovies);
assertTrue(mappedMovies.size()==2);
assertEquals("TheShawshankRedemption",mappedMovies.get(1).getDescription());
}
2）JAVA8直接用流的方法：
@Test
publicvoidconvert_list_to_map_with_java8_lambda(){
List<Movie>movies=newArrayList<Movie>();
movies.add(newMovie(1,"TheShawshankRedemption"));
movies.add(newMovie(2,"TheGodfather"));
Map<Integer,Movie>mappedMovies=movies.stream().collect(
Collectors.toMap(Movie::getRank,(p)->p));
logger.info(mappedMovies);
assertTrue(mappedMovies.size()==2);
assertEquals("TheShawshankRedemption",mappedMovies.get(1).getDescription());
}
3）使用guava工具类库
@Test
publicvoidconvert_list_to_map_with_guava(){
List<Movie>movies=Lists.newArrayList();
movies.add(newMovie(1,"TheShawshankRedemption"));
movies.add(newMovie(2,"TheGodfather"));
Map<Integer,Movie>mappedMovies=Maps.uniqueIndex(movies,newFunction<Movie,Integer>(){
publicIntegerapply(Moviefrom){
returnfrom.getRank();
}});
logger.info(mappedMovies);
assertTrue(mappedMovies.size()==2);
assertEquals("TheShawshankRedemption",mappedMovies.get(1).getDescription());
}
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