For 循环到 Stream
For loops to Stream
我正在学习 Streams 和 ParallelStreams,现在我正在尝试应用它。我正在将包含 for 循环的代码更改为 streams 但我无法更改代码的某些部分。首先,是否可以将此代码缩减为 Streams?
使用 foreach 循环
private List<BasicDBObject> linhaCriativa(List<BasicDBObject> linhas) {
List<BasicDBObject> lista = new ArrayList<>();
for (BasicDBObject db : linhas) {
if (!db.toMap().containsKey("spec_linha-criativa")) {
lista.add(db);
continue;
}
String[] linhaCriativa = db.get("spec_linha-criativa").toString().split(";");
if (linhaCriativa.length > 0) {
for (String criativa : linhaCriativa) {
BasicDBObject dbObject = (BasicDBObject) db.copy();
dbObject.replace("spec_linha-criativa", criativa);
lista.add(dbObject);
}
} else {
lista.add(db);
}
}
return lista;
}
我可以做到这一点,但是当 db.toMap().containsKey("spec_linha-criativa")
时我做不到
List<BasicDBObject> notContains = linhas.parallelStream().filter(m -> !m.toMap().containsKey("spec_linha-criativa")).collect(Collectors.toList());
如果我对您的代码的理解正确,对于输入列表中的每个 BasicDBObject,您提取一个或多个 BasicDBObject,并将它们添加到输出列表。
这是一个flatMap()
操作:
return linhas.stream()
.flatMap(this::extractOutputDbObjectsFrom)
.collect(Collectors.toList());
现在您需要创建 extractOutputDbObjectsFrom
方法:
private Stream<BasicDBObject> extractOutputDbObjectsFrom(DbObject db) {
if (!db.toMap().containsKey("spec_linha-criativa")) {
return Stream.of(db);
}
String[] linhaCriativa = db.get("spec_linha-criativa").toString().split(";");
if (linhaCriativa.length > 0) {
return Arrays.stream(linhaCriativa).map(criativa -> {
BasicDBObject dbObject = (BasicDBObject) db.copy();
dbObject.replace("spec_linha-criativa", criativa);
return dbObject;
});
} else {
return Stream.of(db);
}
}
(未测试,但您应该明白)
我正在学习 Streams 和 ParallelStreams,现在我正在尝试应用它。我正在将包含 for 循环的代码更改为 streams 但我无法更改代码的某些部分。首先,是否可以将此代码缩减为 Streams?
使用 foreach 循环
private List<BasicDBObject> linhaCriativa(List<BasicDBObject> linhas) {
List<BasicDBObject> lista = new ArrayList<>();
for (BasicDBObject db : linhas) {
if (!db.toMap().containsKey("spec_linha-criativa")) {
lista.add(db);
continue;
}
String[] linhaCriativa = db.get("spec_linha-criativa").toString().split(";");
if (linhaCriativa.length > 0) {
for (String criativa : linhaCriativa) {
BasicDBObject dbObject = (BasicDBObject) db.copy();
dbObject.replace("spec_linha-criativa", criativa);
lista.add(dbObject);
}
} else {
lista.add(db);
}
}
return lista;
}
我可以做到这一点,但是当 db.toMap().containsKey("spec_linha-criativa")
时我做不到List<BasicDBObject> notContains = linhas.parallelStream().filter(m -> !m.toMap().containsKey("spec_linha-criativa")).collect(Collectors.toList());
如果我对您的代码的理解正确,对于输入列表中的每个 BasicDBObject,您提取一个或多个 BasicDBObject,并将它们添加到输出列表。
这是一个flatMap()
操作:
return linhas.stream()
.flatMap(this::extractOutputDbObjectsFrom)
.collect(Collectors.toList());
现在您需要创建 extractOutputDbObjectsFrom
方法:
private Stream<BasicDBObject> extractOutputDbObjectsFrom(DbObject db) {
if (!db.toMap().containsKey("spec_linha-criativa")) {
return Stream.of(db);
}
String[] linhaCriativa = db.get("spec_linha-criativa").toString().split(";");
if (linhaCriativa.length > 0) {
return Arrays.stream(linhaCriativa).map(criativa -> {
BasicDBObject dbObject = (BasicDBObject) db.copy();
dbObject.replace("spec_linha-criativa", criativa);
return dbObject;
});
} else {
return Stream.of(db);
}
}
(未测试,但您应该明白)