如何在lambdas foreach块中更改外部方法的局部变量？ [英] How to change the local variable of the outer method in the lambdas foreach block?

问题描述

不适用于每个区块：

public void cleanup4(){
    long timestamp = Instant.now().minus(90l, ChronoUnit.DAYS)
            .toEpochMilli();
    String cql = "SELECT * FROM usertoken";
    ResultSet rs = CassandraTools.getInstance().execute(cql,ConsistencyLevel.QUORUM);
    CassandraConverter cassandraConverter=new MappingCassandraConverter();
    CassandraConverterRowCallback<UserTokenCassandra> callback= new CassandraConverterRowCallback<UserTokenCassandra>(cassandraConverter, UserTokenCassandra.class);
    UserTokenCassandra utc = null;
    Iterator<Row> iterator = rs.iterator();
    while (iterator.hasNext()) {
        Row row = iterator.next();
        utc=callback.doWith(row);
        log.info("{}", utc);
        log.info("记录的时间为：{}",
                Instant.ofEpochMilli(utc.getExpireTime()));
        if (timestamp > utc.getExpireTime()) {
            // repository.delete(n);
        }
    }
}

For-each block：

For-each block:

public void cleanup4(){
    long timestamp = Instant.now().minus(90l, ChronoUnit.DAYS)
            .toEpochMilli();
    String cql = "SELECT * FROM usertoken";
    ResultSet rs = CassandraTools.getInstance().execute(cql,ConsistencyLevel.QUORUM);
    CassandraConverter cassandraConverter=new MappingCassandraConverter();
    CassandraConverterRowCallback<UserTokenCassandra> callback= new CassandraConverterRowCallback<UserTokenCassandra>(cassandraConverter, UserTokenCassandra.class);
    rs.forEach(usertoken->{
        UserTokenCassandra utc = null;
        log.info("{}", utc);
        log.info("The Time：{}",
                Instant.ofEpochMilli(utc.getExpireTime()));
        if (timestamp > utc.getExpireTime()) {
            // repository.delete(utc);
        }
    });
}

1. for-each块似乎产生了很多没有使用UserTokenCassandra的引用..这些垃圾吗？
2.So如何编写此代码？

1.The for-each block seems generate a lot no use reference of UserTokenCassandra .. And are these garbage? 2.So How to write this code?

推荐答案

您无法在lambda体内修改外部方法局部变量。在这里，您不需要 forEach 。如 ResultSet 实现 Iterable ，您可以使用增强的代替循环：

You cannot modify the outer method local variable from within the lambda body. Here you don't need the forEach. As ResultSet implements Iterable, you can use enhanced for loop instead:

for(Row row : rs) {
    utc=callback.doWith(row);
    log.info("{}", utc);
    log.info("记录的时间为：{}",
            Instant.ofEpochMilli(utc.getExpireTime()));
    if (timestamp > utc.getExpireTime()) {
        // repository.delete(n);
    }
}

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