Spring Batch 步骤对象-Chunk Tasklet

news2024/11/20 2:26:05

引言

接着上篇：Spring Batch 步骤对象-步骤Step与Tasklet 了解step步骤概念及其使用之后，本篇再来讲解spring batch使用更广，功能更强大的tasklet：居于块的批处理步骤：Chunk Tasklet

简介

居于chunk(块)的Tasklet相对简单Tasklet来说，多了3个模块：ItemReader( 读模块)， ItemProcessor(处理模块)，ItemWriter(写模块)，跟它们名字一样，一个负责数据读，一个负责数据加工，一个负责数据写。

结构图：

时序图：

需求：简单演示chunk Tasklet使用

ItemReader ItemProcessor ItemWriter 都接口，直接使用匿名内部类方式方便创建

package com.langfeiyes.batch._08_step_chunk_tasklet;

import org.springframework.batch.core.Job;
import org.springframework.batch.core.Step;
import org.springframework.batch.core.StepContribution;
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
import org.springframework.batch.core.configuration.annotation.JobBuilderFactory;
import org.springframework.batch.core.configuration.annotation.StepBuilderFactory;
import org.springframework.batch.core.launch.JobLauncher;
import org.springframework.batch.core.launch.support.RunIdIncrementer;
import org.springframework.batch.core.scope.context.ChunkContext;
import org.springframework.batch.core.step.tasklet.Tasklet;
import org.springframework.batch.item.*;
import org.springframework.batch.repeat.RepeatStatus;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import java.util.Arrays;
import java.util.List;

@SpringBootApplication
@EnableBatchProcessing
public class ChunkTaskletJob {
    @Autowired
    private JobLauncher jobLauncher;
    @Autowired
    private JobBuilderFactory jobBuilderFactory;
    @Autowired
    private StepBuilderFactory stepBuilderFactory;


    @Bean
    public ItemReader itemReader(){
        return new ItemReader() {
            @Override
            public Object read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {
                System.out.println("-------------read------------");
                return "read-ret";
            }
        };
    }

    @Bean
    public ItemProcessor itemProcessor(){
        return new ItemProcessor() {
            @Override
            public Object process(Object item) throws Exception {
                System.out.println("-------------process------------>" + item);
                return "process-ret->" + item;
            }
        };
    }
    @Bean
    public ItemWriter itemWriter(){
        return new ItemWriter() {
            @Override
            public void write(List items) throws Exception {
                System.out.println(items);
            }
        };
    }
    @Bean
    public Step step1(){
        return stepBuilderFactory.get("step1")
                .chunk(3)  //设置块的size为3次
                .reader(itemReader())
                .processor(itemProcessor())
                .writer(itemWriter())
                .build();
    }
    //定义作业
    @Bean
    public Job job(){
        return jobBuilderFactory.get("step-chunk-tasklet-job")
                .start(step1())
                .incrementer(new RunIdIncrementer())
                .build();
    }
    public static void main(String[] args) {
        SpringApplication.run(ChunkTaskletJob.class, args);
    }
}

执行完了之后结果

-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret
-------------process------------>read-ret
-------------process------------>read-ret
[process-ret->read-ret, process-ret->read-ret, process-ret->read-ret]
-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret
-------------process------------>read-ret
-------------process------------>read-ret
[process-ret->read-ret, process-ret->read-ret, process-ret->read-ret]
-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret
-------------process------------>read-ret
-------------process------------>read-ret
[process-ret->read-ret, process-ret->read-ret, process-ret->read-ret]
....

观察上面打印结果，得出2个得出。

1>程序一直在循环打印，先循环打印3次reader，再循环打印3次processor，最后一次性输出3个值。

2>死循环重复上面步骤

问题来了，为啥会出现这种效果，该怎么改进？

其实这个是ChunkTasklet 执行特点，ItemReader会一直循环读，直到返回null，才停止。而processor也是一样，itemReader读多少次，它处理多少次， itemWriter 一次性输出当前次输入的所有数据。

我们改进一下上面案例，要求只读3次，只需要改动itemReader方法就行

int timer = 3;
@Bean
public ItemReader itemReader(){
    return new ItemReader() {
        @Override
        public Object read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {

            if(timer > 0){
                System.out.println("-------------read------------");
                return  "read-ret-" + timer--;
            }else{
                return null;
            }

        }
    };
}

结果不在死循环了

-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret-3
-------------process------------>read-ret-2
-------------process------------>read-ret-1
[process-ret->read-ret-3, process-ret->read-ret-2, process-ret->read-ret-1]

思考一个问题，如果将timer改为 10，而 .chunk(3) 不变结果会怎样？

-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret-10
-------------process------------>read-ret-9
-------------process------------>read-ret-8
[process-ret->read-ret-10, process-ret->read-ret-9, process-ret->read-ret-8]
-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret-7
-------------process------------>read-ret-6
-------------process------------>read-ret-5
[process-ret->read-ret-7, process-ret->read-ret-6, process-ret->read-ret-5]
-------------read------------
-------------read------------
-------------read------------
-------------process------------>read-ret-4
-------------process------------>read-ret-3
-------------process------------>read-ret-2
[process-ret->read-ret-4, process-ret->read-ret-3, process-ret->read-ret-2]
-------------read------------
-------------process------------>read-ret-1
[process-ret->read-ret-1]

找出规律了嘛？

当chunkSize = 3 表示 reader 先读3次，提交给processor处理3次，最后由writer输出3个值

timer =10，表示数据有10条，一个批次(趟)只能处理3条数据，需要4个批次(趟)来处理。

是不是有批处理味道出来

结论：chunkSize 表示：一趟需要ItemReader读多少次，ItemProcessor要处理多少次。

到这，本篇就结束了，欲知后事如何，请听下回分解~