blocks|key|1700643|text|用一个字段是不可能的。但是，您可以使用类型参数创建另一个方法/+getter：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1700644|public+<T>+BiFunction<String,+Class<T>,+MongoCollection<T>>+getCollectionFactory()+{
++++return++(collectionName,+typeParameterClass)+->+{
++++++++return+mongoClient
++++++++++++++++.getDatabase(mongodbConfiguration.getDatabase())
++++++++++++++++.getCollection(collectionName,+typeParameterClass);
++++};
};|code-block|syntax|javascript|1700645|请记住，在调用方法时必须指定类型：|1700646|repository.<Category>.getCollectionFactory().apply("test",+Category.class)|1700647|或者使用具有显式类型的变量：|1700648|BiFunction<String,+Class<Category>,+MongoCollection<Category>>+factory+=+repository.getCollectionFactory();
factory.apply("test",+Category.class)|1700649|当然，您已经可以使用常规的旧getCollection方法来完成这个任务了：|offset|length|style|CODE|1700650|BiFunction<String,+Class<Category>,+MongoCollection<Category>>+factory+=+repository::getCollection;|1700651|因此，工厂方法的有效性是值得怀疑的。|1700652|entityMap^0|0|0|0|0|0|0|E|D|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|16|8|@$Q|17|R|18|S|T]]|9|@]|A|$]]|$1|U|3|V|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

That's not possible with a field. You can however create another method / getter with a type parameter:
<pre class="lang-java prettyprint-override"><code>public &lt;T&gt; BiFunction&lt;String, Class&lt;T&gt;, MongoCollection&lt;T&gt;&gt; getCollectionFactory() {
 return (collectionName, typeParameterClass) -&gt; {
 return mongoClient
 .getDatabase(mongodbConfiguration.getDatabase())
 .getCollection(collectionName, typeParameterClass);
 };
};
</code></pre>
Keep in mind you have to specify the type when calling the method:
<pre class="lang-java prettyprint-override"><code>repository.&lt;Category&gt;.getCollectionFactory().apply(&quot;test&quot;, Category.class)
</code></pre>
Or use a variable with an explicit type:
<pre class="lang-java prettyprint-override"><code>BiFunction&lt;String, Class&lt;Category&gt;, MongoCollection&lt;Category&gt;&gt; factory = repository.getCollectionFactory();
factory.apply(&quot;test&quot;, Category.class)
</code></pre>
Of course, you can already do this with the regular old <code>getCollection</code> method:
<pre class="lang-java prettyprint-override"><code>BiFunction&lt;String, Class&lt;Category&gt;, MongoCollection&lt;Category&gt;&gt; factory = repository::getCollection;
</code></pre>
So the usefulness of the factory method is questionable.

blocks|key|1700681|text|BiFunction错误的第三种类型(结果类型)应该是MongoCollection<T>|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1700682|public+BiFunction<String,+Class<T>,+MongoCollection<T>>+getCollection+=+(name,+type)+->+
++++mongoClient
++++++++.getDatabase(mongodbConfiguration.getDatabase())
++++++++.getCollection(name,+type);|code-block|syntax|javascript|1700683|还要注意，T必须是类泛型参数，只要getCollection不再是一个方法，而是一个字段。|1700684|public+class+ClassHavingGetCollectionField<T>+{
+++...
}|1700685|..。否则，您需要定义一个泛型类型返回此类功能接口实现的方法：|1700686|public+<T>+BiFunction<String,+Class<T>,+MongoCollection<T>>+getCollectionBiFunction()+{
++++return+(name,+type)+->
+++++++++mongoClient
+++++++++++++.getDatabase(mongodbConfiguration.getDatabase())
+++++++++++++.getCollection(name,+type);
}|1700687|entityMap^0|0|A|R|I|0|0|5|1|H|D|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|16|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|T|$]]

The <code>BiFunction</code> has wrong the third type (the result type) that should be <code>MongoCollection&lt;T&gt;</code>:
<pre><code>public BiFunction&lt;String, Class&lt;T&gt;, MongoCollection&lt;T&gt;&gt; getCollection = (name, type) -&gt; 
 mongoClient
 .getDatabase(mongodbConfiguration.getDatabase())
 .getCollection(name, type);
</code></pre>
Also note the <code>T</code> must be the class generic parameter as long as <code>getCollection</code> is no longer a method but a field.
<pre><code>public class ClassHavingGetCollectionField&lt;T&gt; {
 ...
}
</code></pre>
... otherwise you need to define a method with a generic type returning such functional interface implementation:
<pre><code>public &lt;T&gt; BiFunction&lt;String, Class&lt;T&gt;, MongoCollection&lt;T&gt;&gt; getCollectionBiFunction() {
 return (name, type) -&gt;
 mongoClient
 .getDatabase(mongodbConfiguration.getDatabase())
 .getCollection(name, type);
}
</code></pre>

I am not sure can we write the generic method as a function programming using Java 8 lamda expression as below
Generic method
<pre><code>public &lt;T&gt; MongoCollection&lt;T&gt; getCollection(String collectionName, Class&lt;T&gt; typeParameterClass) {
 return mongoClient
 .getDatabase(mongodbConfiguration.getDatabase())
 .getCollection(collectionName, typeParameterClass);
}
</code></pre>
I want to convert this generic method to generic functional lamda expression as below
<pre><code>public BiFunction&lt;String, Class&lt;T&gt;, T&gt; getCollection = (collectionName, typeParameterClass) -&gt; {
 return mongoClient
 .getDatabase(mongodbConfiguration.getDatabase())
 .getCollection(collectionName, typeParameterClass);
};
</code></pre>
From the above code I have an error on type <code>T</code> and <code>typeParameterClass</code>
<a href="https://i.stack.imgur.com/8Opti.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8Opti.png" alt="enter image description here" /></a>
Update 1
While implementing the method suggested by @Clashsoft the second argumenent is <code>Class&lt;Object&gt;</code> instead of <code>Class&lt;T&gt;</code>
<pre><code>repository.getCollectionFactory().apply(&quot;&quot;, Category.class);
</code></pre>
<a href="https://i.stack.imgur.com/JVGYS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JVGYS.png" alt="enter image description here" /></a>

Generic method as functional programming using java.util.Function

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

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我不确定是否可以使用Java 8 lamda表达式将泛型方法编写为函数编程，如下所示泛型方法public <T> MongoCollection<T> getCollection(String collectionName, Class<T> typeParameterClass) { return mongoC...

问用java.util.Function作为函数编程的泛型方法
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