JavaSE ThreadLocal

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ThreadLocal?とは？ †

• 各スレッドで一意になるオブジェクト
• J2EE上の業務ロジック・DAOで、一回の呼び出しの中で持ち回る値を格納する

  HTTP REQ --> |Servlet --> 業務ロジック --> DAO1|
  HTTP RES <-- |                         --> DAO2|
  (通常１回の処理要求は１スレッドで処理される）

  • JDBC Connection
  • ユーザ名
  • 権限情報
  • など*1を Servlet 業務ロジック DAO1 DAO2 で取り出せるようにする

ThreadLocal?なオブジェクトの作り方 †

• java.lang.ThreadLocal?<T> を継承
• protected void <T> initialValue() を @Override
  • このメソッドの返値が、ThreadLocal?になる
• ThreadLocal?なオブジェクトを取り出すには
  • <T> ThreadLocal?#get()

ThreadLocalMap? †

• その名の通り ThreadLocal? な Map
• "ServiceContext?" 基底クラス

  package com.snail;
  
  import java.util.Collection;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Set;
  
  public class ThreadLocalMap extends ThreadLocal<Map<Object, Object>> implements
  		Map<Object, Object> {
  
  	@Override
  	protected Map<Object, Object> initialValue() {
  		return new LinkedHashMap<Object, Object>();
  	}
  
  	public void clear() {
  		((Map<Object, Object>) get()).clear();
  
  	}
  
  	public boolean containsKey(Object key) {
  		return ((Map<Object, Object>) get()).containsKey(key);
  	}
  
  	public boolean containsValue(Object value) {
  		return ((Map<Object, Object>) get()).containsValue(value);
  	}
  
  	public Set<java.util.Map.Entry<Object, Object>> entrySet() {
  		return ((Map<Object, Object>) get()).entrySet();
  	}
  
  	public Object get(Object key) {
  		return ((Map<Object, Object>) get()).get(key);
  	}
  
  	public boolean isEmpty() {
  		return ((Map<Object, Object>) get()).isEmpty();
  	}
  
  	public Set<Object> keySet() {
  		return ((Map<Object, Object>) get()).keySet();
  	}
  
  	public Object put(Object key, Object value) {
  		return ((Map<Object, Object>) get()).put(key, value);
  	}
  
  	public void putAll(Map<? extends Object, ? extends Object> m) {
  		((Map<Object, Object>) get()).putAll(m);
  
  	}
  
  	public Object remove(Object key) {
  		return ((Map<Object, Object>) get()).remove(key);
  	}
  
  	public int size() {
  		return ((Map<Object, Object>) get()).size();
  	}
  
  	public Collection<Object> values() {
  		return ((Map<Object, Object>) get()).values();
  	}
  }
  

ThreadLocalMap?のテストクラス †

package com.snail;

import java.util.Map;


public class ThreadLocalExam {
	
	static Map<Object,Object> map = new ThreadLocalMap();

	public static void main(String[] args) {
		
		
		Child child1 = new Child("SAKURA");
		Child child2 = new Child("MOMO");
		Child child3 = new Child("KAEDE");
		
		child1.start();
		child2.start();
		child3.start();
	}
	
	static class Child extends Thread{
		private String name;
		
		public Child(String pName){
			name = pName;
		}
		
		@Override
		public void run(){
			
			System.out.println("THREAD-" + this.getId() + " SET \"" + name + "\" TO MAP");
			map.put("NAME", name);
			
			try {
				Thread.sleep(3000L);
			} catch (InterruptedException ignoreEx) {
				ignoreEx = null;
			}
			
			System.out.println("THREAD-" + this.getId() + " GET NAME FROM MAP : " + name );
		}
	}

}

THREAD-8  SET "SAKURA" TO MAP
THREAD-9  SET "MOMO" TO MAP
THREAD-10 SET "KAEDE" TO MAP

THREAD-8  GET NAME FROM MAP : SAKURA
THREAD-10 GET NAME FROM MAP : KAEDE
THREAD-9  GET NAME FROM MAP : MOMO

確かにスレッドローカルなMapになっているようだ

ServiceContext?(参考) †

public class ServiceContext extends ThreadLocalMap{
  public Connection getConnection(){
    return (Connection)this.get("CONNECTION");
  }
  public void setConnection( Connection conn ){
    this.put("CONNECTION",conn);
  }
  public Sring getUserName(){
    return (String)this.get("USER_NAME");
  }
  public void setUserName( String userName ){
    this.put("USER_NAME",userName);
  }
  …
}

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