java - 由于使用 java8 lambdas 时出现无效类型异常，Flink 无法运行我的应用程序

Question

我正在使用 Flink 和 Java8。将 lambda 函数与元组和泛型类型一起使用时，我的编译器以异常结束

    /Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/bin/java -Didea.launcher.port=7536 "-Didea.launcher.bin.path=/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath "/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/tools.jar:/Users/hasan.guercan/Git/flink-java-project/target/classes:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-java/1.0.3/flink-java-1.0.3.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-core/1.0.3/flink-core-1.0.3.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-annotations/1.0.3/flink-annotations-1.0.3.jar:/Users/hasan.guercan/.m2/repository/com/esotericsoftware/kryo/kryo/2.24.0/kryo-2.24.0.jar:/Users/hasan.guercan/.m2/repository/com/esotericsoftware/minlog/minlog/1.2/minlog-1.2.jar:/Users/hasan.guercan/.m2/repository/org/objenesis/objenesis/2.1/objenesis-2.1.jar:/Users/hasan.guercan/.m2/repository/org/apache/avro/avro/1.7.6/avro-1.7.6.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-shaded-hadoop2/1.0.3/flink-shaded-hadoop2-1.0.3.jar:/Users/hasan.guercan/.m2/repository/xmlenc/xmlenc/0.52/xmlenc-0.52.jar:/Users/hasan.guercan/.m2/repository/commons-codec/commons-codec/1.4/commons-codec-1.4.jar:/Users/hasan.guercan/.m2/repository/commons-io/commons-io/2.4/commons-io-2.4.jar:/Users/hasan.guercan/.m2/repository/commons-net/commons-net/3.1/commons-net-3.1.jar:/Users/hasan.guercan/.m2/repository/commons-collections/commons-collections/3.2.1/commons-collections-3.2.1.jar:/Users/hasan.guercan/.m2/repository/javax/servlet/servlet-api/2.5/servlet-api-2.5.jar:/Users/hasan.guercan/.m2/repository/org/mortbay/jetty/jetty-util/6.1.26/jetty-util-6.1.26.jar:/Users/hasan.guercan/.m2/repository/com/sun/jersey/jersey-core/1.9/jersey-core-1.9.jar:/Users/hasan.guercan/.m2/repository/commons-el/commons-el/1.0/commons-el-1.0.jar:/Users/hasan.guercan/.m2/repository/commons-logging/commons-logging/1.1.3/commons-logging-1.1.3.jar:/Users/hasan.guercan/.m2/repository/com/jamesmurty/utils/java-xmlbuilder/0.4/java-xmlbuilder-0.4.jar:/Users/hasan.guercan/.m2/repository/commons-lang/commons-lang/2.6/commons-lang-2.6.jar:/Users/hasan.guercan/.m2/repository/commons-configuration/commons-configuration/1.7/commons-configuration-1.7.jar:/Users/hasan.guercan/.m2/repository/commons-digester/commons-digester/1.8.1/commons-digester-1.8.1.jar:/Users/hasan.guercan/.m2/repository/org/codehaus/jackson/jackson-core-asl/1.8.8/jackson-core-asl-1.8.8.jar:/Users/hasan.guercan/.m2/repository/org/codehaus/jackson/jackson-mapper-asl/1.8.8/jackson-mapper-asl-1.8.8.jar:/Users/hasan.guercan/.m2/repository/com/thoughtworks/paranamer/paranamer/2.3/paranamer-2.3.jar:/Users/hasan.guercan/.m2/repository/org/xerial/snappy/snappy-java/1.0.5/snappy-java-1.0.5.jar:/Users/hasan.guercan/.m2/repository/com/jcraft/jsch/0.1.42/jsch-0.1.42.jar:/Users/hasan.guercan/.m2/repository/org/apache/zookeeper/zookeeper/3.4.6/zookeeper-3.4.6.jar:/Users/hasan.guercan/.m2/repository/io/netty/netty/3.7.0.Final/netty-3.7.0.Final.jar:/Users/hasan.guercan/.m2/repository/org/apache/commons/commons-compress/1.4.1/commons-compress-1.4.1.jar:/Users/hasan.guercan/.m2/repository/org/tukaani/xz/1.0/xz-1.0.jar:/Users/hasan.guercan/.m2/repository/commons-beanutils/commons-beanutils-bean-collections/1.8.3/commons-beanutils-bean-collections-1.8.3.jar:/Users/hasan.guercan/.m2/repository/commons-daemon/commons-daemon/1.0.13/commons-daemon-1.0.13.jar:/Users/hasan.guercan/.m2/repository/javax/xml/bind/jaxb-api/2.2.2/jaxb-api-2.2.2.jar:/Users/hasan.guercan/.m2/repository/javax/xml/stream/stax-api/1.0-2/stax-api-1.0-2.jar:/Users/hasan.guercan/.m2/repository/javax/activation/activation/1.1/activation-1.1.jar:/Users/hasan.guercan/.m2/repository/com/google/inject/guice/3.0/guice-3.0.jar:/Users/hasan.guercan/.m2/repository/javax/inject/javax.inject/1/javax.inject-1.jar:/Users/hasan.guercan/.m2/repository/aopalliance/aopalliance/1.0/aopalliance-1.0.jar:/Users/hasan.guercan/.m2/repository/org/apache/commons/commons-math3/3.5/commons-math3-3.5.jar:/Users/hasan.guercan/.m2/repository/org/slf4j/slf4j-api/1.7.7/slf4j-api-1.7.7.jar:/Users/hasan.guercan/.m2/repository/org/slf4j/slf4j-log4j12/1.7.7/slf4j-log4j12-1.7.7.jar:/Users/hasan.guercan/.m2/repository/log4j/log4j/1.2.17/log4j-1.2.17.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/force-shading/1.0.3/force-shading-1.0.3.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-streaming-java_2.10/1.0.3/flink-streaming-java_2.10-1.0.3.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-runtime_2.10/1.0.3/flink-runtime_2.10-1.0.3.jar:/Users/hasan.guercan/.m2/repository/io/netty/netty-all/4.0.27.Final/netty-all-4.0.27.Final.jar:/Users/hasan.guercan/.m2/repository/org/javassist/javassist/3.18.2-GA/javassist-3.18.2-GA.jar:/Users/hasan.guercan/.m2/repository/org/scala-lang/scala-library/2.10.4/scala-library-2.10.4.jar:/Users/hasan.guercan/.m2/repository/com/typesafe/akka/akka-actor_2.10/2.3.7/akka-actor_2.10-2.3.7.jar:/Users/hasan.guercan/.m2/repository/com/typesafe/config/1.2.1/config-1.2.1.jar:/Users/hasan.guercan/.m2/repository/com/typesafe/akka/akka-remote_2.10/2.3.7/akka-remote_2.10-2.3.7.jar:/Users/hasan.guercan/.m2/repository/com/google/protobuf/protobuf-java/2.5.0/protobuf-java-2.5.0.jar:/Users/hasan.guercan/.m2/repository/org/uncommons/maths/uncommons-maths/1.2.2a/uncommons-maths-1.2.2a.jar:/Users/hasan.guercan/.m2/repository/com/typesafe/akka/akka-slf4j_2.10/2.3.7/akka-slf4j_2.10-2.3.7.jar:/Users/hasan.guercan/.m2/repository/org/clapper/grizzled-slf4j_2.10/1.0.2/grizzled-slf4j_2.10-1.0.2.jar:/Users/hasan.guercan/.m2/repository/com/github/scopt/scopt_2.10/3.2.0/scopt_2.10-3.2.0.jar:/Users/hasan.guercan/.m2/repository/io/dropwizard/metrics/metrics-core/3.1.0/metrics-core-3.1.0.jar:/Users/hasan.guercan/.m2/repository/io/dropwizard/metrics/metrics-jvm/3.1.0/metrics-jvm-3.1.0.jar:/Users/hasan.guercan/.m2/repository/io/dropwizard/metrics/metrics-json/3.1.0/metrics-json-3.1.0.jar:/Users/hasan.guercan/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.4.2/jackson-databind-2.4.2.jar:/Users/hasan.guercan/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.4.0/jackson-annotations-2.4.0.jar:/Users/hasan.guercan/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.4.2/jackson-core-2.4.2.jar:/Users/hasan.guercan/.m2/repository/com/twitter/chill_2.10/0.7.4/chill_2.10-0.7.4.jar:/Users/hasan.guercan/.m2/repository/com/twitter/chill-java/0.7.4/chill-java-0.7.4.jar:/Users/hasan.guercan/.m2/repository/org/apache/commons/commons-math/2.2/commons-math-2.2.jar:/Users/hasan.guercan/.m2/repository/org/apache/sling/org.apache.sling.commons.json/2.0.6/org.apache.sling.commons.json-2.0.6.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-clients_2.10/1.0.3/flink-clients_2.10-1.0.3.jar:/Users/hasan.guercan/.m2/repository/org/apache/flink/flink-optimizer_2.10/1.0.3/flink-optimizer_2.10-1.0.3.jar:/Users/hasan.guercan/.m2/repository/commons-cli/commons-cli/1.2/commons-cli-1.2.jar:/Users/hasan.guercan/.m2/repository/org/apache/commons/commons-lang3/3.0.1/commons-lang3-3.0.1.jar:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar" com.intellij.rt.execution.application.AppMain org.apache.flink.quickstart.exercise2.ReplyGraph
Exception in thread "main" org.apache.flink.api.common.functions.InvalidTypesException: The return type of function 'retrieve(ReplyGraph.java:33)' could not be determined automatically, due to type erasure. You can give type information hints by using the returns(...) method on the result of the transformation call, or by letting your function implement the 'ResultTypeQueryable' interface.
    at org.apache.flink.api.java.DataSet.getType(DataSet.java:178)
    at org.apache.flink.api.java.DataSet.collect(DataSet.java:407)
    at org.apache.flink.api.java.DataSet.print(DataSet.java:1605)
    at org.apache.flink.quickstart.exercise2.ReplyGraph.retrieve(ReplyGraph.java:41)
    at org.apache.flink.quickstart.exercise2.ReplyGraph.main(ReplyGraph.java:56)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: org.apache.flink.api.common.functions.InvalidTypesException: The generic type parameters of 'Tuple3' are missing. 
It seems that your compiler has not stored them into the .class file. 
Currently, only the Eclipse JDT compiler preserves the type information necessary to use the lambdas feature type-safely. 
See the documentation for more information about how to compile jobs containing lambda expressions.
    at org.apache.flink.api.java.typeutils.TypeExtractor.validateLambdaGenericParameter(TypeExtractor.java:1316)
    at org.apache.flink.api.java.typeutils.TypeExtractor.validateLambdaGenericParameters(TypeExtractor.java:1302)
    at org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:346)
    at org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:304)
    at org.apache.flink.api.java.typeutils.TypeExtractor.getMapReturnTypes(TypeExtractor.java:119)
    at org.apache.flink.api.java.DataSet.map(DataSet.java:215)
    at org.apache.flink.quickstart.exercise2.ReplyGraph.retrieve(ReplyGraph.java:33)
    ... 6 more

所以我必须至少创建一个匿名类来解决这个问题。第一个代码片段表示导致所述异常的代码:

DataSet<MailEntry> filteredUserReplyMails = replyMails.filter(entryTuple -> {
            String sender = entryTuple.getField(1).toString();
            return !sender.contains("git@") && !sender.contains("jira@");
        }).map((entry -> {
            MailEntry mailEntry = new MailEntry();
            mailEntry.messageId = entry.f0.replaceAll("<", "").replaceAll(">", "");
            mailEntry.sender = entry.f1;
            mailEntry.replyTo = entry.f2;
            return mailEntry;
        });

下一个在创建匿名类时起作用:

DataSet<MailEntry> filteredUserReplyMails = replyMails.filter(entryTuple -> {
            String sender = entryTuple.getField(1).toString();
            return !sender.contains("git@") && !sender.contains("jira@");
        }).map(new MapFunction<Tuple3<String, String, String>, MailEntry>() {
            @Override
            public MailEntry map(Tuple3<String, String, String> entry) throws Exception {
                MailEntry mailEntry = new MailEntry();
                mailEntry.messageId = entry.f0.replaceAll("<", "").replaceAll(">", "");
                mailEntry.sender = entry.f1;
                mailEntry.replyTo = entry.f2;
                return mailEntry;
            }
        });

Java lambda 函数非常简洁。如何在不创建匿名类的情况下解决这个问题？

Answer 1

尝试在 map 之后使用 returns 方法:

DataSet<MailEntry> filteredUserReplyMails = replyMails.filter(entryTuple -> {
            String sender = entryTuple.getField(1).toString();
            return !sender.contains("git@") && !sender.contains("jira@");
        }).map(entry -> {
            MailEntry mailEntry = new MailEntry();
            mailEntry.messageId = entry.f0.replaceAll("<", "").replaceAll(">", "");
            mailEntry.sender = entry.f1;
            mailEntry.replyTo = entry.f2;
            return mailEntry;
        }).returns(MailEntry.class);