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/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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);