Spring Batch的核心概念

如下图，JobLancher启动job，一个job包含若干step，每个step又包含一个ItemReader（读数据），ItemProcessor（处理数据），和ItemWriter（输出数据），job的元数据和运行状态则存储在JobRepository中。

Spring batch主要有以下部分组成

JobRepository 　　用来注册job的容器
JobLauncher 用来启动Job的接口
Job 实际执行的任务，包含一个或多个Step
Step step包含ItemReader、ItemProcessor和ItemWriter
ItemReader 用来读取数据的接口
ItemProcessor 用来处理数据的接口
ItemWriter 用来输出数据的接口

以上Spring Batch的主要组成部分只需要注册成Spring的Bean即可。若想开启批处理的支持还需在配置类上使用@EnableBatchProcessing，在Spring Batch中提供了大量的ItemReader和ItemWriter的实现，用来读取不同的数据来源，数据的处理和校验都要通过ItemProcessor接口实现来完成。

Job运行时概念

Job的一次完整运行称为一个JobInstance，由JobParameter区分（Spring认为相同的Job不应该多次运行），即如果JobParameter相同则为同一个Job，而一次运行如果中途失败或者抛异常，再次运行仍为一个JobInstance，而其中的每次运行称为一个JobExecution。执行一个step称为StepExecution

关系如下：

Job 1->n JobInstance 1->n JobExecution 1->n StepExecution

JobExecution和StepExecution各包含一个ExecutionContext，其中存储了key-value对，可以用来存储运行状态。

框架实践

下面这个例子实现的是：从变量中读取3个字符串全转化大写并输出到控制台，加了一个监听，当任务完成时输出一个字符串到控制台，通过web端来调用。

版本说明：

spring-boot:2.0.1.RELEASE
spring-batch-4.0.1.RELEASE(Spring-Boot 2.0.1就是依赖的此版本)

POM文件：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.javainuse</groupId>
    <artifactId>springboot-batch</artifactId>
    <version>0.0.1</version>
    <packaging>jar</packaging>

    <name>SpringBatch</name>
    <description>Spring Batch-Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.1.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-batch</artifactId>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

Item Reader

读取：从数组中读取3个字符串

package com.javainuse.step;

import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.NonTransientResourceException;
import org.springframework.batch.item.ParseException;
import org.springframework.batch.item.UnexpectedInputException;

public class Reader implements ItemReader<String> {

    private String[] messages = { "javainuse.com", 
            "Welcome to Spring Batch Example",
            "We use H2 Database for this example" };

    private int count = 0;

    @Override
    public String read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {

        if (count < messages.length) {
            return messages[count++];
        } else {
            count = 0;
        }
        return null;
    }
    
}

Item Processor

处理：将字符串转为大写

package com.javainuse.step;

import org.springframework.batch.item.ItemProcessor;

public class Processor implements ItemProcessor<String, String> {
    
    @Override
    public String process(String data) throws Exception {
        return data.toUpperCase();
    }
    
}

Item Writer

输出：把转为大写的字符串输出到控制台

package com.javainuse.step;

import java.util.List;

import org.springframework.batch.item.ItemWriter;

public class Writer implements ItemWriter<String> {
    
    @Override
    public void write(List<? extends String> messages) throws Exception {
        for (String msg : messages) {
            System.out.println("Writing the data " + msg);
        }
    }
    
}

Listener

监听：任务成功完成后往控制台输出一行字符串

package com.javainuse.listener;

import org.springframework.batch.core.BatchStatus;
import org.springframework.batch.core.JobExecution;
import org.springframework.batch.core.listener.JobExecutionListenerSupport;

public class JobCompletionListener extends JobExecutionListenerSupport {
    
    @Override
    public void afterJob(JobExecution jobExecution) {
        if (jobExecution.getStatus() == BatchStatus.COMPLETED) {
            System.out.println("BATCH JOB COMPLETED SUCCESSFULLY");
        }
    }
    
}

Config

Spring Boot配置

package com.javainuse.config;

import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobExecutionListener;
import org.springframework.batch.core.Step;
import org.springframework.batch.core.configuration.annotation.JobBuilderFactory;
import org.springframework.batch.core.configuration.annotation.StepBuilderFactory;
import org.springframework.batch.core.launch.support.RunIdIncrementer;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.javainuse.listener.JobCompletionListener;
import com.javainuse.step.Processor;
import com.javainuse.step.Reader;
import com.javainuse.step.Writer;

@Configuration
public class BatchConfig {

    @Autowired
    public JobBuilderFactory jobBuilderFactory;

    @Autowired
    public StepBuilderFactory stepBuilderFactory;

    @Bean
    public Job processJob() {
        return jobBuilderFactory.get("processJob")
                .incrementer(new RunIdIncrementer()).listener(listener())
                .flow(orderStep1()).end().build();
    }

    @Bean
    public Step orderStep1() {
        return stepBuilderFactory.get("orderStep1").<String, String> chunk(1)
                .reader(new Reader()).processor(new Processor())
                .writer(new Writer()).build();
    }

    @Bean
    public JobExecutionListener listener() {
        return new JobCompletionListener();
    }
    
}

Controller

控制器：配置web路由，访问/invokejob来调用任务

package com.javainuse.controller;
 
import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobParameters;
import org.springframework.batch.core.JobParametersBuilder;
import org.springframework.batch.core.launch.JobLauncher;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class JobInvokerController {
 
    @Autowired
    JobLauncher jobLauncher;
 
    @Autowired
    Job processJob;
 
    @RequestMapping("/invokejob")
    public String handle() throws Exception {
 
            JobParameters jobParameters = new JobParametersBuilder().addLong("time", System.currentTimeMillis())
                    .toJobParameters();
            jobLauncher.run(processJob, jobParameters);
 
        return "Batch job has been invoked";
    }
}

application.properties

配置：Spring Batch在加载的时候job默认都会执行，把spring.batch.job.enabled置为false，即把job设置成不可用，应用便会根据jobLauncher.run来执行。下面2行是数据库的配置，不配置也可以，使用的嵌入式数据库h2。

spring.batch.job.enabled=false
spring.datasource.url=jdbc:h2:file:./DB
spring.jpa.properties.hibernate.hbm2ddl.auto=update

Application

Spring Boot入口类：加注解@EnableBatchProcessing

package com.javainuse;

import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@EnableBatchProcessing
public class SpringBatchApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBatchApplication.class, args);
    }
}

进阶

方案一：spring boot上构建spring batch远程分区Step

https://gitee.com/kailing/partitionjob

方案二：spring batch进阶-基于RabbitMQ远程分区Step

http://www.kailing.pub/article/index/arcid/196.html

参考：

https://jamie-wang.iteye.com/blog/1876320

查了十几个帖子总结，如有侵权请联系作者。

Spring Batch 使用指南

Spring Batch的核心概念

Spring batch主要有以下部分组成

Job运行时概念

框架实践

进阶

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