Use Javadoc's -linkoffline instead of -link

`-link` does I/O to download the package list, for every javadoc
invocation. There is no caching, so this happens many times per build.
Swap to offline mode to avoid spamming the servers, and avoid build
failures if the servers aren't entirely healthy.

all/build.gradle

@@ -49,7 +49,7 @@ tasks.named("javadoc").configure {
             continue;
         }
         source subproject.javadoc.source
-        options.links subproject.javadoc.options.links.toArray(new String[0])
+        options.linksOffline.addAll subproject.javadoc.options.linksOffline
     }
 }
 

build.gradle

@@ -207,7 +207,8 @@ subprojects {
             options {
                 encoding = 'UTF-8'
                 use = true
-                links 'https://docs.oracle.com/javase/8/docs/api/'
+                linksOffline 'https://docs.oracle.com/javase/8/docs/api/',
+		    "${rootProject.projectDir}/gradle/javadoc/docs.oracle.com-javase-8-docs-api/"
                 source = "8"
             }
         }

gradle/javadoc/docs.oracle.com-javase-8-docs-api/package-list

@@ -0,0 +1,217 @@
+java.applet
+java.awt
+java.awt.color
+java.awt.datatransfer
+java.awt.dnd
+java.awt.event
+java.awt.font
+java.awt.geom
+java.awt.im
+java.awt.im.spi
+java.awt.image
+java.awt.image.renderable
+java.awt.print
+java.beans
+java.beans.beancontext
+java.io
+java.lang
+java.lang.annotation
+java.lang.instrument
+java.lang.invoke
+java.lang.management
+java.lang.ref
+java.lang.reflect
+java.math
+java.net
+java.nio
+java.nio.channels
+java.nio.channels.spi
+java.nio.charset
+java.nio.charset.spi
+java.nio.file
+java.nio.file.attribute
+java.nio.file.spi
+java.rmi
+java.rmi.activation
+java.rmi.dgc
+java.rmi.registry
+java.rmi.server
+java.security
+java.security.acl
+java.security.cert
+java.security.interfaces
+java.security.spec
+java.sql
+java.text
+java.text.spi
+java.time
+java.time.chrono
+java.time.format
+java.time.temporal
+java.time.zone
+java.util
+java.util.concurrent
+java.util.concurrent.atomic
+java.util.concurrent.locks
+java.util.function
+java.util.jar
+java.util.logging
+java.util.prefs
+java.util.regex
+java.util.spi
+java.util.stream
+java.util.zip
+javax.accessibility
+javax.activation
+javax.activity
+javax.annotation
+javax.annotation.processing
+javax.crypto
+javax.crypto.interfaces
+javax.crypto.spec
+javax.imageio
+javax.imageio.event
+javax.imageio.metadata
+javax.imageio.plugins.bmp
+javax.imageio.plugins.jpeg
+javax.imageio.spi
+javax.imageio.stream
+javax.jws
+javax.jws.soap
+javax.lang.model
+javax.lang.model.element
+javax.lang.model.type
+javax.lang.model.util
+javax.management
+javax.management.loading
+javax.management.modelmbean
+javax.management.monitor
+javax.management.openmbean
+javax.management.relation
+javax.management.remote
+javax.management.remote.rmi
+javax.management.timer
+javax.naming
+javax.naming.directory
+javax.naming.event
+javax.naming.ldap
+javax.naming.spi
+javax.net
+javax.net.ssl
+javax.print
+javax.print.attribute
+javax.print.attribute.standard
+javax.print.event
+javax.rmi
+javax.rmi.CORBA
+javax.rmi.ssl
+javax.script
+javax.security.auth
+javax.security.auth.callback
+javax.security.auth.kerberos
+javax.security.auth.login
+javax.security.auth.spi
+javax.security.auth.x500
+javax.security.cert
+javax.security.sasl
+javax.sound.midi
+javax.sound.midi.spi
+javax.sound.sampled
+javax.sound.sampled.spi
+javax.sql
+javax.sql.rowset
+javax.sql.rowset.serial
+javax.sql.rowset.spi
+javax.swing
+javax.swing.border
+javax.swing.colorchooser
+javax.swing.event
+javax.swing.filechooser
+javax.swing.plaf
+javax.swing.plaf.basic
+javax.swing.plaf.metal
+javax.swing.plaf.multi
+javax.swing.plaf.nimbus
+javax.swing.plaf.synth
+javax.swing.table
+javax.swing.text
+javax.swing.text.html
+javax.swing.text.html.parser
+javax.swing.text.rtf
+javax.swing.tree
+javax.swing.undo
+javax.tools
+javax.transaction
+javax.transaction.xa
+javax.xml
+javax.xml.bind
+javax.xml.bind.annotation
+javax.xml.bind.annotation.adapters
+javax.xml.bind.attachment
+javax.xml.bind.helpers
+javax.xml.bind.util
+javax.xml.crypto
+javax.xml.crypto.dom
+javax.xml.crypto.dsig
+javax.xml.crypto.dsig.dom
+javax.xml.crypto.dsig.keyinfo
+javax.xml.crypto.dsig.spec
+javax.xml.datatype
+javax.xml.namespace
+javax.xml.parsers
+javax.xml.soap
+javax.xml.stream
+javax.xml.stream.events
+javax.xml.stream.util
+javax.xml.transform
+javax.xml.transform.dom
+javax.xml.transform.sax
+javax.xml.transform.stax
+javax.xml.transform.stream
+javax.xml.validation
+javax.xml.ws
+javax.xml.ws.handler
+javax.xml.ws.handler.soap
+javax.xml.ws.http
+javax.xml.ws.soap
+javax.xml.ws.spi
+javax.xml.ws.spi.http
+javax.xml.ws.wsaddressing
+javax.xml.xpath
+org.ietf.jgss
+org.omg.CORBA
+org.omg.CORBA.DynAnyPackage
+org.omg.CORBA.ORBPackage
+org.omg.CORBA.TypeCodePackage
+org.omg.CORBA.portable
+org.omg.CORBA_2_3
+org.omg.CORBA_2_3.portable
+org.omg.CosNaming
+org.omg.CosNaming.NamingContextExtPackage
+org.omg.CosNaming.NamingContextPackage
+org.omg.Dynamic
+org.omg.DynamicAny
+org.omg.DynamicAny.DynAnyFactoryPackage
+org.omg.DynamicAny.DynAnyPackage
+org.omg.IOP
+org.omg.IOP.CodecFactoryPackage
+org.omg.IOP.CodecPackage
+org.omg.Messaging
+org.omg.PortableInterceptor
+org.omg.PortableInterceptor.ORBInitInfoPackage
+org.omg.PortableServer
+org.omg.PortableServer.CurrentPackage
+org.omg.PortableServer.POAManagerPackage
+org.omg.PortableServer.POAPackage
+org.omg.PortableServer.ServantLocatorPackage
+org.omg.PortableServer.portable
+org.omg.SendingContext
+org.omg.stub.java.rmi
+org.w3c.dom
+org.w3c.dom.bootstrap
+org.w3c.dom.events
+org.w3c.dom.ls
+org.w3c.dom.views
+org.xml.sax
+org.xml.sax.ext
+org.xml.sax.helpers

gradle/javadoc/netty.io-4.1-api/package-list

@@ -0,0 +1,77 @@
+io.netty.bootstrap
+io.netty.buffer
+io.netty.buffer.search
+io.netty.channel
+io.netty.channel.embedded
+io.netty.channel.epoll
+io.netty.channel.group
+io.netty.channel.internal
+io.netty.channel.kqueue
+io.netty.channel.local
+io.netty.channel.nio
+io.netty.channel.oio
+io.netty.channel.pool
+io.netty.channel.rxtx
+io.netty.channel.sctp
+io.netty.channel.sctp.nio
+io.netty.channel.sctp.oio
+io.netty.channel.socket
+io.netty.channel.socket.nio
+io.netty.channel.socket.oio
+io.netty.channel.udt
+io.netty.channel.udt.nio
+io.netty.channel.unix
+io.netty.handler.address
+io.netty.handler.codec
+io.netty.handler.codec.base64
+io.netty.handler.codec.bytes
+io.netty.handler.codec.compression
+io.netty.handler.codec.dns
+io.netty.handler.codec.haproxy
+io.netty.handler.codec.http
+io.netty.handler.codec.http.cookie
+io.netty.handler.codec.http.cors
+io.netty.handler.codec.http.multipart
+io.netty.handler.codec.http.websocketx
+io.netty.handler.codec.http.websocketx.extensions
+io.netty.handler.codec.http.websocketx.extensions.compression
+io.netty.handler.codec.http2
+io.netty.handler.codec.json
+io.netty.handler.codec.marshalling
+io.netty.handler.codec.memcache
+io.netty.handler.codec.memcache.binary
+io.netty.handler.codec.mqtt
+io.netty.handler.codec.protobuf
+io.netty.handler.codec.redis
+io.netty.handler.codec.rtsp
+io.netty.handler.codec.sctp
+io.netty.handler.codec.serialization
+io.netty.handler.codec.smtp
+io.netty.handler.codec.socks
+io.netty.handler.codec.socksx
+io.netty.handler.codec.socksx.v4
+io.netty.handler.codec.socksx.v5
+io.netty.handler.codec.spdy
+io.netty.handler.codec.stomp
+io.netty.handler.codec.string
+io.netty.handler.codec.xml
+io.netty.handler.flow
+io.netty.handler.flush
+io.netty.handler.ipfilter
+io.netty.handler.logging
+io.netty.handler.pcap
+io.netty.handler.proxy
+io.netty.handler.ssl
+io.netty.handler.ssl.ocsp
+io.netty.handler.ssl.util
+io.netty.handler.stream
+io.netty.handler.timeout
+io.netty.handler.traffic
+io.netty.resolver
+io.netty.resolver.dns
+io.netty.resolver.dns.macos
+io.netty.util
+io.netty.util.collection
+io.netty.util.concurrent
+io.netty.util.internal
+io.netty.util.internal.logging

gradle/javadoc/protobuf.dev-reference-java-api-docs/package-list

@@ -0,0 +1,3 @@
+com.google.protobuf
+com.google.protobuf.compiler
+com.google.protobuf.util

gradle/javadoc/square.github.io-okhttp-2.x-okhttp/package-list

@@ -0,0 +1 @@
+com.squareup.okhttp

netty/build.gradle

@@ -77,7 +77,8 @@ import net.ltgt.gradle.errorprone.CheckSeverity
 }
 
 tasks.named("javadoc").configure {
-    options.links 'http://netty.io/4.1/api/'
+    options.linksOffline 'https://netty.io/4.1/api/',
+        "${rootProject.projectDir}/gradle/javadoc/netty.io-4.1-api/"
     exclude 'io/grpc/netty/*Provider.java'
     exclude 'io/grpc/netty/GrpcHttp2ConnectionHandler.java'
     exclude 'io/grpc/netty/Internal*'

okhttp/build.gradle

@@ -45,7 +45,8 @@ tasks.named("checkstyleMain").configure {
 }
 
 tasks.named("javadoc").configure {
-    options.links 'http://square.github.io/okhttp/2.x/okhttp/'
+    options.linksOffline 'https://square.github.io/okhttp/2.x/okhttp/',
+        "${rootProject.projectDir}/gradle/javadoc/square.github.io-okhttp-2.x-okhttp/"
     exclude 'io/grpc/okhttp/Internal*'
     exclude 'io/grpc/okhttp/*Provider.java'
     exclude 'io/grpc/okhttp/internal/**'

protobuf/build.gradle

@@ -36,5 +36,6 @@ dependencies {
 }
 
 tasks.named("javadoc").configure {
-    options.links 'https://protobuf.dev/reference/java/api-docs/'
+    options.linksOffline 'https://protobuf.dev/reference/java/api-docs/',
+        "${rootProject.projectDir}/gradle/javadoc/protobuf.dev-reference-java-api-docs/"
 }