主要内容：实现Flink写数据到MySQL，即MySQL Sink。

准备工作

Flink自身并没有提供连接MySQL的连接器，需要手动引入：

<!-- mysql connector -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.44</version>
</dependency>

代码实现

核心代码在于：

streaming.addSink(new MyJdbcSink).setParallelism(1)

这里你需要1个参数：

• MyJdbcSink：自定义的JdbcSink。需要注意的是，实现该方法时要继承RichSinkFunction函数，可利用open()函数初始化JDBC连接、SQL预编译器等运行时环境，也可以利用close()函数做清理工作。若选择继承SinkFunction，会在每次写入一条数据时都会创建一个JDBC连接。源码注解中给出的解释：

Writes the given value to the sink. This function is called for every record.

完整代码如下：

package org.ourhome.streamapi

import java.sql.{Connection, DriverManager, PreparedStatement}

import org.apache.flink.streaming.api.scala._
import org.apache.flink.api.java.utils.ParameterTool
import org.apache.flink.configuration.Configuration
import org.apache.flink.runtime.state.filesystem.FsStateBackend
import org.apache.flink.streaming.api.CheckpointingMode
import org.apache.flink.streaming.api.functions.sink.{RichSinkFunction, SinkFunction}
import org.apache.flink.streaming.api.scala.{DataStream, StreamExecutionEnvironment}
/**
 * @Author Do
 * @Date 2020/4/18 22:23
 */
object MysqlSinkTest {
  private val URL: String = "jdbc:mysql://ip:port/database?characterEncoding=utf8&useSSL=false"
  private val USER: String = "root"
  private val PASSWORD: String = "123456"

  def main(args: Array[String]): Unit = {
    val params: ParameterTool = ParameterTool.fromArgs(args)
    val runType:String = params.get("runtype")
    println("runType: " + runType)

    val env: StreamExecutionEnvironment = StreamExecutionEnvironment.getExecutionEnvironment
    env.getCheckpointConfig.setCheckpointingMode(CheckpointingMode.EXACTLY_ONCE)
    env.enableCheckpointing(5000) // checkpoint every 5000
    env.setStateBackend(new FsStateBackend("file:///D:/Work/Code/flinkdev/src/main/resources/checkpoint"))

    val inputStream: DataStream[String] = env.socketTextStream("host", 9000)
    // 处理inputStream，包装成Person类
    val streaming: DataStream[Person] = inputStream.map(line => {
      println(line)
      val strings: Array[String] = line.split(",")
      Person(strings(0).trim, strings(1).trim.toInt, strings(2).trim, strings(3).trim.toFloat)
    })

    streaming.addSink(new MyJdbcSink).setParallelism(1)

    env.execute("Mysql Sink")

  }

  case class Person (name: String, age: Int, gender: String, height: Float)

  /**
   * 若选择SinkFunction "Writes the given value to the sink. This function is called for every record."
   * RichFunction有生命周期和初始化配置功能，在初始化时创建连接，后面直接调用连接
   */
  class MyJdbcSink extends RichSinkFunction[Person] {
    // 定义一些变量：JDBC连接、sql预编译器()
    var conn: Connection = _
    var updateStmt: PreparedStatement = _
    var insertStmt: PreparedStatement = _

    // open函数用于初始化富函数运行时的上下文等环境，如JDBC连接
    override def open(parameters: Configuration): Unit = {
      println("----------------------------open函数初始化JDBC连接及预编译sql-------------------------")
      super.open(parameters)
      conn = DriverManager.getConnection(URL, USER, PASSWORD)
      insertStmt = conn.prepareStatement("INSERT INTO person_message (name, age, gender, height) VALUES (?, ?, ?, ?)")
      updateStmt = conn.prepareStatement("UPDATE person_message set age = ?, gender = ?, height = ? where name = ?")
    }
    // 调JDBC连接，执行SQL
    override def invoke(value: Person, context: SinkFunction.Context[_]): Unit = {
      println("-------------------------执行sql---------------------------")
      // 执行更新语句
      updateStmt.setInt(1, value.age)
      updateStmt.setString(2, value.gender)
      updateStmt.setDouble(3, value.height)
      updateStmt.setString(4, value.name)
      updateStmt.execute()
      // 如果update没有查到数据，那么执行insert语句
      if (updateStmt.getUpdateCount == 0) {
        insertStmt.setString(1, value.name)
        insertStmt.setInt(2, value.age)
        insertStmt.setString(3, value.gender)
        insertStmt.setDouble(4, value.height)
        insertStmt.execute()
      }
    }
    // 关闭时做清理工作
    override def close(): Unit = {
      println("-----------------------关闭连接，并释放资源-----------------------")
      updateStmt.close()
      insertStmt.close()
      conn.close()
    }
  }

}

Socket发送数据：

nc -lk 9999
小明,20,man,180.2
小红,22,woman,178.4
小黑,18,man,192.9
小兰,19,woman,188.0
小爱,30,woman,177.3

输出：

--------------open函数初始化JDBC连接及预编译sql---------------

小明,20,man,180.2
-------------------------执行sql---------------------------
小红,22,woman,178.4
-------------------------执行sql---------------------------
小黑,18,man,192.9
-------------------------执行sql---------------------------
小兰,19,woman,188.0
-------------------------执行sql---------------------------
小爱,30,woman,177.3
-------------------------执行sql---------------------------

--------------------关闭连接，并释放资源----------------------

可见，程序会先调用open()函数，创建JDBC连接及预编译SQL，然后使用该链接多次执行SQL语句，最终调用close()函数关闭连接释放资源。注意：代码里需要将并行度设置为了1，以便观察运行机制。

MySQL表数据：

注意：需要提前创建表person_message。