本文主要总结线程共享数据的相关知识，主要包括两方面:一是某个线程内如何共享数据，保证各个线程的数据不交叉；一是多个线程间如何共享数据，保证数据的一致性。
自己实现的话，是定义一个Map,线程为键，数据为值,表中的每一项即是为每个线程准备的数据,这样在一个线程中数据是一致的。
例子
package com.iot.thread;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
/**
* Created by brian on 2016/2/4.
*/
public class ThreadScopeShareData {
//准备一个哈希表，为每个线程准备数据
private static Map<Thread,Integer> threadData = new HashMap<>();
public static void main(String[] args) {
for (int i=0;i<2;i++){
new Thread(
new Runnable() {
@Override
public void run() {
int data = new Random().nextint();
threadData.put(Thread.currentThread(),data);
System.out.println(Thread.currentThread()+" put data："+data);
new A().get();
new B().get();
}
}
).start();
}
}
static class A{
public void get(){
int data = threadData.get(Thread.currentThread());
System.out.println("A from "+Thread.currentThread()+" get data "+data);
}
}
static class B{
public void get(){
int data = threadData.get(Thread.currentThread());
System.out.println("B from "+Thread.currentThread()+" get data "+data);
}
}
}
上述代码偶尔会报异常：
Exception in thread "Thread-0" java.lang.NullPointerException
at com.iot.thread.ThreadScopeShareData$A.get(ThreadScopeShareData.java:29)
at com.iot.thread.ThreadScopeShareData$1.run(ThreadScopeShareData.java:21)
at java.lang.Thread.run(Thread.java:745)
具体原因还不知道
API:
java.lang:Class ThreadLocal<T>
使用ThreadLocal类型的对象代替上面的Map即可
定义一个对象来封装多个变量，然后在ThreadLocal中存储整个对象
多变量时，最好将ThreadLocal类放在数据类的内部，数据类采用单例模式，这样，新建对象和获取对象都会更方便，同时封装性更强。
package com.iot.thread;
import java.util.Random;
/**
* Created by brian on 2016/2/4.
*/
public class ThreadLocalTest {
private static ThreadLocal<Integer> threadInger = new ThreadLocal<>();
public static void main(String[] args) {
for (int i=0;i<2;i++){
new Thread(new Runnable() {
@Override
public void run() {
int data = new Random().nextint(100);
threadInger.set(data);
System.out.println(Thread.currentThread()+" put data："+data);
MyThreadScopeData.getThreadInstance().setName(Thread.currentThread().toString());
MyThreadScopeData.getThreadInstance().setAge(data%10);
new A().get();
new B().get();
}
}
).start();
}
}
static class A{
public void get(){
int data = threadInger.get();
System.out.println("A from "+Thread.currentThread()+" get data "+data);
MyThreadScopeData myThreadScopeData = MyThreadScopeData.getThreadInstance();
System.out.println("A from "+myThreadScopeData);
}
}
static class B{
public void get(){
int data = threadInger.get();
System.out.println("B from "+Thread.currentThread()+" get data "+data);
MyThreadScopeData myThreadScopeData = MyThreadScopeData.getThreadInstance();
System.out.println("B from "+myThreadScopeData);
}
}
}
/**
* 将多变量封装起来的数据类
* 单例模式，内置ThreadLocal类型变量
*/
class MyThreadScopeData{
private MyThreadScopeData(){
}
private static ThreadLocal<MyThreadScopeData> data = new ThreadLocal<>();
public static MyThreadScopeData getThreadInstance(){
MyThreadScopeData instance = data.get();
if(instance == null){
instance = new MyThreadScopeData();
data.set(instance);
}
return instance;
}
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
String reVal = super.toString()+"-{name,age}"+":{"+getName()+","+getAge()+"}";
return reVal;
}
}
几种方式
最后一种方式的示例:
设计5个线程，其中三个线程每次对j增加1，另外两个线程对j每次减少1
package com.iot.thread;
/**
* Created by brian on 2016/2/4.
*/
public class MutiThreadShareData {
private static MutiShareData mutiShareData = new MutiShareData();
public static void main(String[] args) {
for (int i=0;i<3;i++){
new Thread(
new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread()+":{j from "+ mutiShareData.getJ()+" + to: "+mutiShareData.increment()+"}");
}
}
).start();
}
for (int i=0;i<2;i++){
new Thread(
new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread()+":{j from "+ mutiShareData.getJ()+" - to: "+mutiShareData.decrement()+"}");
}
}
).start();
}
}
}
/**
* 将共享数据封装在另一对象中（操作数据的方法也在该对象完成）
*/
class MutiShareData{
private int j = 0;
public synchronized int increment(){
return ++j;
}
public synchronized int decrement(){
return --j;
}
public synchronized int getJ() {
return j;
}
public synchronized void setJ(int j) {
this.j = j;
}
}
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