如何解决此 Java 类型安全警告？
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How to solve this Java type safety warning?
提问by Nicolas Raoul
Map session = ActionContext.getContext().getSession();
session.put("user", user);
This code generates a warning: Type safety: The method put(Object, Object) belongs to the raw type Map. References to generic type Map<K,V> should be parameterized.
此代码生成警告：类型安全：方法 put(Object, Object) 属于原始类型 Map。对泛型类型 Map<K,V> 的引用应该被参数化。
Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession();
session.put("user", user);
This code generates a warning: Type safety: Unchecked cast from Map to Map<String,Serializable>.
此代码生成警告：类型安全：未检查从 Map 到 Map<String,Serializable> 的强制转换。
The getSessionmethod belongs to Struts2 so I can't modify it. I would like to avoid using @SuppressWarnings because other warnings can be useful.
该的getSession方法属于Struts2的，所以我不能修改它。我想避免使用 @SuppressWarnings，因为其他警告可能很有用。
I guess all Struts2 users in the world faced the same problem... is there an elegant solution?
我猜世界上所有的 Struts2 用户都面临着同样的问题……有没有一个优雅的解决方案？
采纳答案by Andrei Fierbinteanu
I don't think there's any other way but @SuppressWarnings("unchecked"). I believe you can put it just above the line in question, and it will only suppress that line.
我认为除了@SuppressWarnings("unchecked") 之外别无他法。我相信你可以把它放在有问题的线上方，它只会抑制那条线。
Edit: you can also do Map<?, ?> session = ActionContext.getContext().getSession();but I'm not sure how willing you are to do that; you won't be able to put anything into the map that way (since the compiler can't check the type of what you're putting), only read from it.
编辑：您也可以这样做，Map<?, ?> session = ActionContext.getContext().getSession();但我不确定您是否愿意这样做；您将无法以这种方式将任何内容放入地图中（因为编译器无法检查您放置的内容的类型），只能从中读取。
回答by zed_0xff
What if you do it like this:
如果你这样做怎么办：
Map<String, Serializable> session = ActionContext.getContext().getSession();
回答by Tommi
What version of Struts 2 (especially XWork) are you using? For me, your following code gives an error:
XWork您使用的是什么版本的 Struts 2（尤其是）？对我来说，您的以下代码给出了错误：
Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession();
session.put("user", user);
Cannot cast from Map<String,Object> to Map<String,Serializable>.
This, on the other hand, works and gives no warnings:
另一方面，这有效并且没有警告：
Map<String, Object> session = ActionContext.getContext().getSession();
回答by Stephen C
The safest, most efficient way to deal with this is probably:
处理这个问题最安全、最有效的方法可能是：
Map<?, ?> session = ActionContext.getContext().getSession();
and then type cast the objects retrieved from the session map.
然后键入从会话映射中检索到的对象。
The @SuppressWarnings approach will actually result in compiled code that is identical. However the type cast will be implicit; i.e. it won't be easy to spot by looking at the source code. And the @SuppressWarnings annotation could (hypothetically) suppress some otherwarning in the same code block that represents a real error; i.e. one that will result in one of the hidden typecasts, etc failing at runtime.
@SuppressWarnings 方法实际上会导致编译后的代码完全相同。然而，类型转换将是隐式的；即通过查看源代码不容易发现。并且@SuppressWarnings 注释可以（假设）抑制同一代码块中代表真正错误的一些其他警告；即会导致隐藏类型转换之一等在运行时失败。
Other more expensive alternatives include:
其他更昂贵的替代品包括：
an entry by entry copy from the
Map<?, ?>to a newMap<String, Serializable>instance casting the keys and values toStringandSerializablerespectively, ora generic method like the following that performs the typecast safely.
一个条目从一个条目复制
Map<?, ?>到一个新Map<String, Serializable>实例String，Serializable分别将键和值投射到和，或者像下面这样的通用方法可以安全地执行类型转换。
@SuppressWarnings("unchecked")
public <K,V> Map<K,V> castMap(Map<?, ?> map, Class<K> kClass, Class<V> vClass) {
for (Map.Entry<?, ?> entry : map.entrySet()) {
kClass.cast(entry.getKey());
vClass.cast(entry.getValue());
}
return (Map<K,V>) map;
}
回答by user3828314
It is requesting you to parameterize the value, if the value needs parameters then pass them.
它要求您参数化该值，如果该值需要参数则传递它们。
For example
例如
Map<Integer, Map> vCombinedCodeMap = new HashMap<>();
will give warning for "parameterized" Map<Integer, Map>.
将对 "parameterized" 发出警告Map<Integer, Map>。
so the correct format is the following:
所以正确的格式如下：
Map<Integer, Map<String, String>> vCombinedCodeMap = new HashMap<>();
回答by Satish Shah
Cast as Following,
铸造如下，
public void setSession(Map<String, Object> sessionMap) {
// TODO Auto-generated method stub
this.sessionMap = (SessionMap<String, Object>) sessionMap;
}
回答by karthik
just write @SuppressWarnings("unchecked")at top of the @GETmethod, hope it will help you.
@SuppressWarnings("unchecked")把@GET方法写在上面，希望对你有帮助。
