Quartz中的Job是什么？
联系自己对于定时任务的理解，其实就是对于任务的抽象，所以这个类其实你在不看源码时，可能就已经就猜到了它是一个接口，一搜源码，果然没错：
package org.quartz;
/**
* 定时任务对于任务的抽象
*/
public interface Job {
/**
* 定时任务执行逻辑
*/
void execute(JobExecutionContext context)
throws JobExecutionException;
}
非常简单，是否你再没有看之前，自己也已经构想到了呢？但是这边又引发了另一个类不接，就是JobExecutionContext，但是细想一下，你可能也会觉得在情理之中，因为在执行任务中，可能你需要获取任务信息。然后你可能会想，比如呢？ 在生产环境中，你可能会用到分布式的定时任务，那么你如何让任务判断自己改处理哪些数据信息呢，这个时候你可以获取Job的上下文，针对取余等等方式，避免数据重复处理。
JobExecutionContext源码解析
首先这也是一个接口，由于内部方法有点多，我们挑一个最重要的分析一下：
package org.quartz;
import java.util.Date;
/**
* Job任务执行时获取到的上下文
*/
public interface JobExecutionContext {
...
/**
* 获取任务详细信息
*/
public JobDetail getJobDetail();
...
}
对于这个类的实现类，默认是JobExecutionContextImpl，由于篇幅原因，这个就不做特地展开，因为这个类只是简单的把属性取出，很简单。那接下来，便开始解决读者的下一个以为，什么是JobDetail？
JobDetail源码解析
你可以先猜想一下，这个接口中会包含哪些信息？
我们直接进入它的实现类：
package org.quartz.impl;
import org.quartz.DisallowConcurrentExecution;
import org.quartz.Job;
import org.quartz.JobBuilder;
import org.quartz.JobDataMap;
import org.quartz.JobDetail;
import org.quartz.JobExecutionContext;
import org.quartz.JobKey;
import org.quartz.PersistJobDataAfterExecution;
import org.quartz.Scheduler;
import org.quartz.StatefulJob;
import org.quartz.Trigger;
import org.quartz.utils.ClassUtils;
/**
* 任务相信信息
*/
public class JobDetailImpl implements Cloneable, java.io.Serializable, JobDetail {
private static final long serialVersionUID = -6069784757781506897L;
/**
* 任务名称
*/
private String name;
/**
* 任务所属组
*/
private String group = Scheduler.DEFAULT_GROUP;
/**
* 任务描述
*/
private String description;
/**
* 任务类
*/
private Class<? extends Job> jobClass;
/**
* 任务额外信息
*/
private JobDataMap jobDataMap;
private boolean durability = false;
private boolean shouldRecover = false;
/**
* 任务唯一标识
*/
private transient JobKey key = null;
public JobDetailImpl() {
}
public JobDetailImpl(String name, Class<? extends Job> jobClass) {
this(name, null, jobClass);
}
public JobDetailImpl(String name, String group, Class<? extends Job> jobClass) {
setName(name);
setGroup(group);
setJobClass(jobClass);
}
public JobDetailImpl(String name, String group, Class<? extends Job> jobClass,
boolean durability, boolean recover) {
setName(name);
setGroup(group);
setJobClass(jobClass);
setDurability(durability);
setRequestsRecovery(recover);
}
public String getName() {
return name;
}
public void setName(String name) {
if (name == null || name.trim().length() == 0) {
throw new IllegalArgumentException("Job name cannot be empty.");
}
this.name = name;
this.key = null;
}
public String getGroup() {
return group;
}
public void setGroup(String group) {
if (group != null && group.trim().length() == 0) {
throw new IllegalArgumentException(
"Group name cannot be empty.");
}
if (group == null) {
group = Scheduler.DEFAULT_GROUP;
}
this.group = group;
this.key = null;
}
public String getFullName() {
return group + "." + name;
}
public JobKey getKey() {
if(key == null) {
if(getName() == null)
return null;
key = new JobKey(getName(), getGroup());
}
return key;
}
public void setKey(JobKey key) {
if(key == null)
throw new IllegalArgumentException("Key cannot be null!");
setName(key.getName());
setGroup(key.getGroup());
this.key = key;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Class<? extends Job> getJobClass() {
return jobClass;
}
public void setJobClass(Class<? extends Job> jobClass) {
if (jobClass == null) {
throw new IllegalArgumentException("Job class cannot be null.");
}
if (!Job.class.isAssignableFrom(jobClass)) {
throw new IllegalArgumentException(
"Job class must implement the Job interface.");
}
this.jobClass = jobClass;
}
public JobDataMap getJobDataMap() {
if (jobDataMap == null) {
jobDataMap = new JobDataMap();
}
return jobDataMap;
}
public void setJobDataMap(JobDataMap jobDataMap) {
this.jobDataMap = jobDataMap;
}
...
@Override
public boolean equals(Object obj) {
if (!(obj instanceof JobDetail)) {
return false;
}
JobDetail other = (JobDetail) obj;
if(other.getKey() == null || getKey() == null)
return false;
if (!other.getKey().equals(getKey())) {
return false;
}
return true;
}
@Override
public int hashCode() {
JobKey key = getKey();
return key == null ? 0 : getKey().hashCode();
}
@Override
public Object clone() {
JobDetailImpl copy;
try {
copy = (JobDetailImpl) super.clone();
if (jobDataMap != null) {
copy.jobDataMap = (JobDataMap) jobDataMap.clone();
}
} catch (CloneNotSupportedException ex) {
throw new IncompatibleClassChangeError("Not Cloneable.");
}
return copy;
}
public JobBuilder getJobBuilder() {
JobBuilder b = JobBuilder.newJob()
.ofType(getJobClass())
.requestRecovery(requestsRecovery())
.storeDurably(isDurable())
.usingJobData(getJobDataMap())
.withDescription(getDescription())
.withIdentity(getKey());
return b;
}
}
相信大家对于这些属性部分可以猜到，先讲一个大家可能没有太注意的Java关键字，是在属性key上的transient，这个关键字是用来干什么的呢？是针对于序列化与反序列化时，不对这个字段进行序列化操作的。这么做是为什么呢？我猜测是为了安全起见，以为定时任务是以这个key作为唯一标示的，序列化下把信息泄露可能会造成安全隐患。也可以看下这里重写了hasCode和equals方法，至于为什么这么做，大家应该能意会。这边大家可能对于JobBuilder有些好奇？
JobBuilder源码解析
JobBuilder是定时任务构造器，用于构造一个JobDetail，源码如下：
package org.quartz;
import org.quartz.impl.JobDetailImpl;
import org.quartz.utils.Key;
/**
* 定时任务构造器，用于构造一个JobDetail
*/
public class JobBuilder {
/**
* 任务标识码，用于唯一确定任务
*/
private JobKey key;
private String description;
private Class<? extends Job> jobClass;
/**
* Durability，持久性；如果Job是非持久性的，一旦没有Trigger与其相关联，
* 它就会从Scheduler中被删除。也就是说Job的生命周期和其Trigger是关联的。
*/
private boolean durability;
/**
* RequestsRecovery，如果为true，那么在Scheduler异常中止或者系统异常关闭后，当Scheduler重启后，Job会被重新执行。
*/
private boolean shouldRecover;
private JobDataMap jobDataMap = new JobDataMap();
protected JobBuilder() {
}
public static JobBuilder newJob() {
return new JobBuilder();
}
public static JobBuilder newJob(Class <? extends Job> jobClass) {
JobBuilder b = new JobBuilder();
b.ofType(jobClass);
return b;
}
public JobDetail build() {
JobDetailImpl job = new JobDetailImpl();
job.setJobClass(jobClass);
job.setDescription(description);
if(key == null)
key = new JobKey(Key.createUniqueName(null), null);
job.setKey(key);
job.setDurability(durability);
job.setRequestsRecovery(shouldRecover);
if(!jobDataMap.isEmpty())
job.setJobDataMap(jobDataMap);
return job;
}
public JobBuilder withIdentity(String name) {
key = new JobKey(name, null);
return this;
}
public JobBuilder withIdentity(String name, String group) {
key = new JobKey(name, group);
return this;
}
public JobBuilder withIdentity(JobKey jobKey) {
this.key = jobKey;
return this;
}
public JobBuilder withDescription(String jobDescription) {
this.description = jobDescription;
return this;
}
public JobBuilder ofType(Class <? extends Job> jobClazz) {
this.jobClass = jobClazz;
return this;
}
...
}
一些简单的get、set方法被我删除了，可以看到这个类非常简单，就是作为一个构造器，根据属性构造出一个JobDetail。