spark 结构化stream读写kafka示例

1.创建源kafka主题和目标kafka主题：


2.编写读写kafka的处理代码如下:

from pyspark import SparkConf
from pyspark.sql import SparkSession
import traceback
# import builtins as py_builtin
from pyspark.sql.functions import max
from pyspark.sql.functions import desc
from pyspark.sql.types import StructField, StructType, StringType, LongType
from pyspark.sql.types import *
from pyspark.sql.functions import col, column, expr
from pyspark.sql.functions import *
from pyspark.sql import Row

appname = "test"  # 任务名称
master = "local[*]"  # 单机模式设置
'''
local: 所有计算都运行在一个线程当中，没有任何并行计算，通常我们在本机执行一些测试代码，或者练手，就用这种模式。
local[K]: 指定使用几个线程来运行计算，比如local[4]就是运行4个worker线程。通常我们的cpu有几个core，就指定几个线程，最大化利用cpu的计算能力
local[*]: 这种模式直接帮你按照cpu最多cores来设置线程数了。
'''
# spark_driver_host = "10.0.0.248"

try:
    # conf = SparkConf().setAppName(appname).setMaster(master).set("spark.driver.host", spark_driver_host) # 集群
    conf = SparkConf().setAppName(appname). 
        set('spark.jars.packages', 'org.apache.spark:spark-sql-kafka-0-10_2.11:2.3.0') 
        .set("spark.jars.repositories", 'http://maven.aliyun.com/nexus/content/groups/public/') 
        .setMaster(master)  # 本地
    spark = SparkSession.builder.config(conf=conf).getOrCreate()
    df = spark 
        .readStream 
        .format("kafka") 
        .option("kafka.bootstrap.servers", "localhost:9092") 
        .option("subscribe", "mykafkatest") 
        .load()
    words = df.selectExpr("CAST(key AS STRING)", "CAST(value AS STRING)", "offset", "timestamp")
    schema = StructType() 
        .add("topic", StringType()) 
        .add("age", StringType())

    # 通过from_json，定义schema来解析json
    # res = words.where(instr("value", '{') ==0).select(from_json("value", schema).alias("data")).select("data.*")
    streamSource = words.where(instr("value", 'topic') > 0).select(from_json("value", schema).alias("data")).select(
        "data.*")

    # query = res.writeStream 
    #     .format("console") 
    #     .outputMode("append") 
    #     .start()
    res = streamSource.withColumn('constfield', lit('1'))
    query = res.select(col('age').alias('key'), to_json(struct('topic', 'age','constfield')).alias('value')) 
        .writeStream 
        .format("kafka") 
        .option("kafka.bootstrap.servers", "localhost:9092") 
        .option("topic", "mykafkatestdest") 
        .option("checkpointLocation", '''D:sparksparkspark-2.3.0-bin-hadoop2.7checkpoint''')
        .start()
    query.awaitTermination()

    print('计算成功！')
except:
    traceback.print_exc()  # 返回出错信息
    print('连接出错！')

这样从源kafka主题消费到的消息就会被写入到目标mykafkatestdest主题中

其中注意事项包括： 指定spark.jars.packages包以及json和dataframe字段的转换.

参考文献:https://blog.csdn.net/qq_33689414/article/details/86469267