- 应该如何使用ServletScopes.scopeRequest() http://google-guice.googlecode.com/git/javadoc/com/google/inject/servlet/ServletScopes.html#scopeRequest%28java.util.concurrent.Callable%3CT%3E,%20java.util.Map%3Ccom.google.inject.Key%3C?%3E,%20java.lang.Object%3E%29?
- 我如何获得对
@RequestScoped
Callable 中的对象?
- 有什么意义
seedMap
?它是否意味着覆盖默认绑定?
- 这个方法和有什么区别ServletScopes.continueRequest() http://google-guice.googlecode.com/git/javadoc/com/google/inject/servlet/ServletScopes.html#continueRequest%28java.util.concurrent.Callable%3CT%3E,%20java.util.Map%3Ccom.google.inject.Key%3C?%3E,%20java.lang.Object%3E%29?
回答我自己的问题:
-
ServletScopes.scopeRequest() http://google-guice.googlecode.com/git/javadoc/com/google/inject/servlet/ServletScopes.html#scopeRequest%28java.util.concurrent.Callable%3CT%3E,%20java.util.Map%3Ccom.google.inject.Key%3C?%3E,%20java.lang.Object%3E%29在 a 中运行 Callablenew请求范围。请注意不要跨不同范围引用对象,否则最终会遇到线程问题,例如尝试使用已被另一个请求关闭的数据库连接。
static
或顶级课程是您在这里的朋友。
- 你注入
Callable
在将其传递到之前ServletScopes.scopeRequest() http://google-guice.googlecode.com/git/javadoc/com/google/inject/servlet/ServletScopes.html#scopeRequest%28java.util.concurrent.Callable%3CT%3E,%20java.util.Map%3Ccom.google.inject.Key%3C?%3E,%20java.lang.Object%3E%29。因此,您必须小心您的领域Callable
包含。下面详细介绍这一点。
-
seedMap
允许你注入非范围的对象进入范围。这很危险,所以要小心注射的东西。
-
ServletScopes.continueRequest() http://google-guice.googlecode.com/git/javadoc/com/google/inject/servlet/ServletScopes.html#continueRequest%28java.util.concurrent.Callable%3CT%3E,%20java.util.Map%3Ccom.google.inject.Key%3C?%3E,%20java.lang.Object%3E%29类似,只是它在一个内部运行existing请求范围。它获取当前 HTTP 范围的快照并将其包装在 Callable 中。原始 HTTP 请求完成(您从服务器返回一些响应),但随后在单独的线程中异步完成实际操作。当稍后调用 Callable 时(在该单独的线程中),它将可以访问原始 HttpServletRequest,但不能访问 HTTP 响应或会话。
那么,最好的方法是什么?
如果您不需要将用户对象传递到Callable
:注入Callable
超出请求范围,并将其传递到ServletScopes.scopeRequest() http://google-guice.googlecode.com/git/javadoc/com/google/inject/servlet/ServletScopes.html#scopeRequest%28java.util.concurrent.Callable%3CT%3E,%20java.util.Map%3Ccom.google.inject.Key%3C?%3E,%20java.lang.Object%3E%29. The Callable
只能参考Provider<Foo>
代替Foo
,否则您最终会得到在请求范围之外注入的实例。
如果您需要将用户对象传递到Callable
,继续阅读。
假设您有一个将名称插入数据库的方法。我们有两种方法将名称传递给Callable
.
方法一:使用子模块传递用户对象:
-
Define InsertName
, a Callable
插入数据库:
@RequestScoped
private static class InsertName implements Callable<Boolean>
{
private final String name;
private final Connection connection;
@Inject
public InsertName(@Named("name") String name, Connection connection)
{
this.name = name;
this.connection = connection;
}
@Override
public Boolean call()
{
try
{
boolean nameAlreadyExists = ...;
if (!nameAlreadyExists)
{
// insert the name
return true;
}
return false;
}
finally
{
connection.close();
}
}
}
-
绑定子模块中的所有用户对象并使用 RequestInjector.scopeRequest() 确定可调用范围:
requestInjector.scopeRequest(InsertName.class, new AbstractModule()
{
@Override
protected void configure()
{
bind(String.class).annotatedWith(Names.named("name")).toInstance("John");
}
})
我们实例化一个RequestInjector
在请求之外,它又注入第二个Callable
inside的请求。第二Callable
可以参考Foo
直接(不需要提供者),因为它被注入到请求范围内。
import com.google.common.base.Preconditions;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.servlet.ServletScopes;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.Callable;
/**
* Injects a Callable into a non-HTTP request scope.
* <p/>
* @author Gili Tzabari
*/
public final class RequestInjector
{
private final Map<Key<?>, Object> seedMap = Collections.emptyMap();
private final Injector injector;
/**
* Creates a new RequestInjector.
*/
@Inject
private RequestInjector(Injector injector)
{
this.injector = injector;
}
/**
* Scopes a Callable in a non-HTTP request scope.
* <p/>
* @param <V> the type of object returned by the Callable
* @param callable the class to inject and execute in the request scope
* @param modules additional modules to install into the request scope
* @return a wrapper that invokes delegate in the request scope
*/
public <V> Callable<V> scopeRequest(final Class<? extends Callable<V>> callable,
final Module... modules)
{
Preconditions.checkNotNull(callable, "callable may not be null");
return ServletScopes.scopeRequest(new Callable<V>()
{
@Override
public V call() throws Exception
{
return injector.createChildInjector(modules).getInstance(callable).call();
}
}, seedMap);
}
}
方法2:注入一个Callable
在引用的请求之外Provider<Foo>
. The call()
然后方法可以get()
请求范围内的实际值。 object对象通过a的方式传入seedMap
(我个人认为这种方法违反直觉):
-
Define InsertName
, a Callable
插入数据库。请注意,与方法 1 不同,我们必须使用Providers
:
@RequestScoped
private static class InsertName implements Callable<Boolean>
{
private final Provider<String> name;
private final Provider<Connection> connection;
@Inject
public InsertName(@Named("name") Provider<String> name, Provider<Connection> connection)
{
this.name = name;
this.connection = connection;
}
@Override
public Boolean call()
{
try
{
boolean nameAlreadyExists = ...;
if (!nameAlreadyExists)
{
// insert the name
return true;
}
return false;
}
finally
{
connection.close();
}
}
}
为您想要传入的类型创建虚假绑定。如果不这样做,您将得到:No implementation for String annotated with @com.google.inject.name.Named(value=name) was bound.
https://stackoverflow.com/a/9014552/14731 https://stackoverflow.com/a/9014552/14731解释了为什么需要这样做。
-
用所需的值填充 seedMap:
ImmutableMap<Key<?>, Object> seedMap = ImmutableMap.<Key<?>, Object>of(Key.get(String.class, Names.named("name")), "john");
-
Invoke ServletScopes.scopeRequest()
:
ServletScopes.scopeRequest(injector.getInstance(InsertName.class), seedMap);
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