Merge branch '5.1.x'

Author: jhoeller

spring-test/spring-test.gradle

@@ -72,7 +72,7 @@ dependencies {
 	testCompile("org.apache.tiles:tiles-core:${tiles3Version}", withoutJclOverSlf4J)
 	testCompile("org.apache.tiles:tiles-servlet:${tiles3Version}", withoutJclOverSlf4J)
 	testCompile("org.hsqldb:hsqldb:${hsqldbVersion}")
-	testCompile("org.apache.httpcomponents:httpclient:4.5.7") {
+	testCompile("org.apache.httpcomponents:httpclient:4.5.8") {
 		exclude group: "commons-logging", module: "commons-logging"
 	}
 	testCompile("io.projectreactor.netty:reactor-netty")

spring-web/spring-web.gradle

@@ -37,9 +37,9 @@ dependencies {
 	optional("org.eclipse.jetty:jetty-servlet") {
 		exclude group: "javax.servlet", module: "javax.servlet-api"
 	}
-	optional("org.eclipse.jetty:jetty-reactive-httpclient:1.0.2")
+	optional("org.eclipse.jetty:jetty-reactive-httpclient:1.0.3")
 	optional("com.squareup.okhttp3:okhttp:3.14.0")
-	optional("org.apache.httpcomponents:httpclient:4.5.7") {
+	optional("org.apache.httpcomponents:httpclient:4.5.8") {
 		exclude group: "commons-logging", module: "commons-logging"
 	}
 	optional("org.apache.httpcomponents:httpasyncclient:4.1.4") {

spring-webflux/spring-webflux.gradle

@@ -35,7 +35,7 @@ dependencies {
 	optional("io.undertow:undertow-websockets-jsr:${undertowVersion}") {
 		exclude group: "org.jboss.spec.javax.websocket", module: "jboss-websocket-api_1.1_spec"
 	}
-	optional("org.apache.httpcomponents:httpclient:4.5.7") {
+	optional("org.apache.httpcomponents:httpclient:4.5.8") {
 		exclude group: "commons-logging", module: "commons-logging"
 	}
 	optional("org.jetbrains.kotlin:kotlin-reflect:${kotlinVersion}")
@@ -53,7 +53,7 @@ dependencies {
 	testCompile("org.apache.tomcat:tomcat-util:${tomcatVersion}")
 	testCompile("org.eclipse.jetty:jetty-server")
 	testCompile("org.eclipse.jetty:jetty-servlet")
-	testCompile("org.eclipse.jetty:jetty-reactive-httpclient:1.0.2")
+	testCompile("org.eclipse.jetty:jetty-reactive-httpclient:1.0.3")
 	testCompile("com.squareup.okhttp3:mockwebserver:3.14.0")
 	testCompile("org.jetbrains.kotlin:kotlin-script-runtime:${kotlinVersion}")
 	testCompile(project(":spring-core-coroutines"))

spring-webmvc/spring-webmvc.gradle

@@ -50,7 +50,7 @@ dependencies {
 	testCompile("org.eclipse.jetty:jetty-server") {
 		exclude group: "javax.servlet", module: "javax.servlet"
 	}
-	testCompile("org.apache.httpcomponents:httpclient:4.5.7") {
+	testCompile("org.apache.httpcomponents:httpclient:4.5.8") {
 		exclude group: "commons-logging", module: "commons-logging"
 	}
 	testCompile("commons-fileupload:commons-fileupload:1.4")

src/docs/asciidoc/core/core-beans.adoc

@@ -4425,9 +4425,9 @@ implementation type, consider declaring the most specific return type on your fa
 method (at least as specific as required by the injection points referring to your bean).
 ====
 
-You can also provide all beans of a particular type from the
-`ApplicationContext` by adding the annotation to a field or method that expects an array
-of that type, as the following example shows:
+You can also provide all beans of a particular type from the `ApplicationContext`
+by adding the annotation to a field or method that expects an array of that type,
+as the following example shows:
 
 [source,java,indent=0]
 [subs="verbatim,quotes"]
@@ -4477,8 +4477,8 @@ Note that the standard `javax.annotation.Priority` annotation is not available a
 through `@Order` values in combination with `@Primary` on a single bean for each type.
 ====
 
-Even typed `Map` instances can be autowired as long as the expected key type is `String`. The Map
-values contain all beans of the expected type, and the keys contain the
+Even typed `Map` instances can be autowired as long as the expected key type is `String`.
+The Map values contain all beans of the expected type, and the keys contain the
 corresponding bean names, as the following example shows:
 
 [source,java,indent=0]
@@ -4497,10 +4497,14 @@ corresponding bean names, as the following example shows:
 	}
 ----
 
-By default, the autowiring fails whenever zero candidate beans are available. The
-default behavior is to treat annotated methods, constructors, and fields as
-indicating required dependencies. You can change this behavior as demonstrated, in the
-following example:
+By default, autowiring fails when no matching candidate beans are available for
+a given injection point. In the case of a declared array, collection or map,
+at least one matching element is expected.
+
+The default behavior is to treat annotated methods and fields as indicating
+required dependencies. You can change this behavior as demonstrated in the
+following example, enabling the framework to skip a non-satisfiable injection
+point through marking it as non-required:
 
 [source,java,indent=0]
 [subs="verbatim,quotes"]
@@ -4518,18 +4522,34 @@ following example:
 	}
 ----
 
+A non-required method will not be called at all if its dependency (or one of its
+dependencies in case of multiple arguments) is not available. A non-required field
+will not get populated at all in such case, leaving its default value in place.
+
+Injected constructor and factory method arguments are a special case since the
+'required' flag on `@Autowired` has a somewhat different meaning due to Spring's
+constructor resolution algorithm potentially dealing with multiple constructors.
+Constructor and factory method arguments are effectively required by default but
+with a few special rules in a single-constructor scenario, such as multi-element
+injection points (arrays, collections, maps) resolving to empty instances if no
+matching beans are available. This allows for a common implementation pattern
+where all dependencies can be declared in a unique multi-argument constructor,
+e.g. declared as a single public constructor without an `@Autowired` annotation.
+
 [NOTE]
 ====
-Only one annotated constructor per-class can be marked as required, but multiple
-non-required constructors can be annotated. In that case, each is considered among the
-candidates and Spring uses the greediest constructor whose dependencies can be
+Only one annotated constructor per class can be marked as required, but multiple
+non-required constructors can be annotated. In that case, each is considered among
+the candidates and Spring uses the greediest constructor whose dependencies can be
 satisfied -- that is, the constructor that has the largest number of arguments.
-
-The required attribute of `@Autowired` is recommended over the `@Required` annotation.
-The required attribute indicates that the property is not required for autowiring
-purposes. The property is ignored if it cannot be autowired. `@Required`, on the other
-hand, is stronger in that it enforces the property that was set by any means supported
-by the container. If no value is injected, a corresponding exception is raised.
+The constructor resolution algorithm is the same as for non-annotated classes with
+overloaded constructors, just narrowing the candidates to annotated constructors.
+
+The 'required' attribute of `@Autowired` is recommended over the `@Required` annotation
+on setter methods. The 'required' attribute indicates that the property is not required
+for autowiring purposes. The property is ignored if it cannot be autowired. `@Required`,
+on the other hand, is stronger in that it enforces the property to be set by any means
+supported by the container. If no value is defined, a corresponding exception is raised.
 ====
 
 Alternatively, you can express the non-required nature of a particular dependency