专栏上文章：
Spring Batch(一)：入门案例与详细案例分析 - 掘金 (juejin.cn)
SpringBatch(二)：作业对象 Job - 掘金 (juejin.cn)
SpringBatch(三)：作业与步骤上下文
语文中有个词叫上下文，比如：联系上下文解读一下作者所有表达意思。从这看上下文有环境，语境，氛围的意思。类比到编程，业内也喜欢使用Context表示上下文。比如Spring容器： SpringApplicationContext 。有上下文这个铺垫之后，我们来看下Spring Batch的上下文。
Spring Batch 有2个比较重要的上下文：
-
JobContext
JobContext 绑定 JobExecution 执行对象为Job作业执行提供执行环境(上下文)。
作用：维护JobExecution 对象，实现作业收尾工作，与处理各种作业回调逻辑
-
StepContext
StepContext 绑定 StepExecution 执行对象为Step步骤执行提供执行环境(上下文)。
作用：维护StepExecution 对象，实现步骤收尾工作，与处理各种步骤回调逻辑
1. 执行上下文
除了上面讲的JobContext 作业上下文， StepContext 步骤上线下文外，还有Spring Batch还维护另外一个上下文：ExecutionContext 执行上下文，作用是：数据共享
Spring Batch 中 ExecutionContext 分2大类
-
Job ExecutionContext
作用域：一次作业运行，所有Step步骤间数据共享。
-
Step ExecutionContext：
作用域：一次步骤运行，单个Step步骤间(ItemReader/ItemProcessor/ItemWrite组件间)数据共享。
2. 作业与步骤执行链
3. 作业与步骤引用链
-
作业线
Job---JobInstance---JobContext---JobExecution--ExecutionContext
-
步骤线
Step--StepContext --StepExecution--ExecutionContext
4. 作业上下文API
JobContext context = JobSynchronizationManager.getContext();
JobExecution jobExecution = context.getJobExecution();
Map jobParameters = context.getJobParameters();
Map jobExecutionContext = context.getJobExecutionContext();
5. 步骤上下文API
ChunkContext chunkContext = xxx;
StepContext stepContext = chunkContext.getStepContext();
StepExecution stepExecution = stepContext.getStepExecution();
Map stepExecutionContext = stepContext.getStepExecutionContext();
Map jobExecutionContext = stepContext.getJobExecutionContext();
6. 执行上下文API
ChunkContext chunkContext = xxx;
//步骤
StepContext stepContext = chunkContext.getStepContext();
StepExecution stepExecution = stepContext.getStepExecution();
ExecutionContext executionContext = stepExecution.getExecutionContext();
executionContext.put("key", "value");
//-------------------------------------------------------------------------
//作业
JobExecution jobExecution = stepExecution.getJobExecution();
ExecutionContext executionContext = jobExecution.getExecutionContext();
executionContext.put("key", "value");
7. 综合案例
需求：观察作业ExecutionContext与 步骤ExecutionContext数据共享
分析：
1>定义step1 与step2 2个步骤
2>在step1中设置数据
作业-ExecutionContext 添加： key-step1-job value-step1-job
步骤-ExecutionContext 添加： key-step1-step value-step1-step
3>在step2中打印观察
作业-ExecutionContext 步骤-ExecutionContext
import com.langfeiyes.batch._04_param_incr.DailyTimestampParamIncrementer;
import org.springframework.batch.core.*;
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.listener.JobListenerFactoryBean;
import org.springframework.batch.core.scope.context.ChunkContext;
import org.springframework.batch.core.scope.context.JobContext;
import org.springframework.batch.core.scope.context.JobSynchronizationManager;
import org.springframework.batch.core.scope.context.StepContext;
import org.springframework.batch.core.step.tasklet.Tasklet;
import org.springframework.batch.item.ExecutionContext;
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;
@SpringBootApplication
@EnableBatchProcessing
public class ExecutionContextJob {
@Autowired
private JobBuilderFactory jobBuilderFactory;
@Autowired
private StepBuilderFactory stepBuilderFactory;
@Bean
public Tasklet tasklet1(){
return new Tasklet() {
@Override
public RepeatStatus execute(StepContribution contribution, ChunkContext chunkContext) throws Exception {
//步骤
ExecutionContext stepEC = chunkContext.getStepContext().getStepExecution().getExecutionContext();
stepEC.put("key-step1-step","value-step1-step");
System.out.println("------------------1---------------------------");
//作业
ExecutionContext jobEC = chunkContext.getStepContext().getStepExecution().getJobExecution().getExecutionContext();
jobEC.put("key-step1-job","value-step1-job");
return RepeatStatus.FINISHED;
}
};
}
@Bean
public Tasklet tasklet2(){
return new Tasklet() {
@Override
public RepeatStatus execute(StepContribution contribution, ChunkContext chunkContext) throws Exception {
//步骤
ExecutionContext stepEC = chunkContext.getStepContext().getStepExecution().getExecutionContext();
System.err.println(stepEC.get("key-step1-step"));
System.out.println("------------------2---------------------------");
//作业
ExecutionContext jobEC = chunkContext.getStepContext().getStepExecution().getJobExecution().getExecutionContext();
System.err.println(jobEC.get("key-step1-job"));
return RepeatStatus.FINISHED;
}
};
}
@Bean
public Step step1(){
return stepBuilderFactory.get("step1")
.tasklet(tasklet1())
.build();
}
@Bean
public Step step2(){
return stepBuilderFactory.get("step2")
.tasklet(tasklet2())
.build();
}
@Bean
public Job job(){
return jobBuilderFactory.get("execution-context-job")
.start(step1())
.next(step2())
.incrementer(new RunIdIncrementer())
.build();
}
public static void main(String[] args) {
SpringApplication.run(ExecutionContextJob.class, args);
}
}
运行结果：
可以看出，在stepContext 设置的参数作用域仅在StepExecution 执行范围有效，而JobContext 设置参数作用与在所有StepExcution 有效，有点局部与全局 的意思。
打开数据库观察表：batch_job_execution_context 跟 batch_step_execution_context 表
JobContext数据保存到：batch_job_execution_context
StepContext数据保存到：batch_step_execution_context
总结：
步骤数据保存在Step ExecutionContext，只能在Step中使用，作业数据保存在Job ExecutionContext，可以在所有Step中共享
