在javaWeb项目中,一般会用单例模式来加载配置文件以及数据字典,有三种方法:
方式一:懒汉方式(到第一次使用实例时,才加载实例)好处是只有到第一次调用getInstance才生成对象,节省了空间。不足之处在于同步锁导致有可能执行过慢。
方式二:饿汉方式 由于BasicConfiguration的实例是static,因此,当类被加载时就会初始化,但这样即使并不需要使用此实例,也会被初始化,导致内存空间的浪费;
方式三:内部类方式 由于初始化放在内部类中,只有当此内部类被使用时,才会进行初始化。从而既节省了空间,也无需同步代码。
先准备测试程序:
- package org.jediael.util;
- import static org.junit.Assert.*;
- import org.junit.Test;
- public class BasicConfigurationTest {
- @Test
- public void testGetValue(){
- BasicConfiguration configuration = BasicConfiguration.getInstance();
- assertTrue(configuration.getValue("key").equals("value"));
- }
- }
其中properties文件中有一行如下:
key=value
优先选择方案三
方式一:懒汉方式
到第一次使用实例时,才加载实例
- package org.jediael.util;
- import java.io.FileInputStream;
- import java.io.FileNotFoundException;
- import java.io.IOException;
- import java.io.InputStream;
- import java.util.Properties;
- public class BasicConfiguration {
- private static BasicConfiguration configuration = null;
- private Properties pros = null;
- public static synchronized BasicConfiguration getInstance(){
- if(configuration == null){
- configuration = new BasicConfiguration();
- }
- return configuration;
- }
- public String getValue(String key){
- return pros.getProperty(key);
- }
- private BasicConfiguration(){
- readConfig();
- }
- private void readConfig() {
- pros = new Properties();
- InputStream in = null;
- try {
- in = new FileInputStream(Thread.currentThread().getContextClassLoader().getResource("")
- .getPath() + "search.properties");
- pros.load(in);
- } catch (FileNotFoundException e) {
- e.printStackTrace();
- }catch (IOException e) {
- e.printStackTrace();
- }finally{
- try {
- in.close();
- } catch (IOException e) {
- e.printStackTrace();
- }
- }
- }
- }
好处是只有到第一次调用getInstance才生成对象,节省了空间。不足之处在于同步锁导致有可能执行过慢。
2、饿汉方式
- package org.jediael.util;
- import java.io.FileInputStream;
- import java.io.FileNotFoundException;
- import java.io.IOException;
- import java.io.InputStream;
- import java.util.Properties;
- public class BasicConfiguration {
- private static BasicConfiguration configuration = new BasicConfiguration();
- private Properties pros = null;
- public static BasicConfiguration getInstance(){
- return configuration;
- }
- public String getValue(String key){
- return pros.getProperty(key);
- }
- private BasicConfiguration(){
- readConfig();
- }
- private void readConfig() {
- pros = new Properties();
- InputStream in = null;
- try {
- in = new FileInputStream(Thread.currentThread().getContextClassLoader().getResource("")
- .getPath() + "search.properties");
- pros.load(in);
- } catch (FileNotFoundException e) {
- e.printStackTrace();
- }catch (IOException e) {
- e.printStackTrace();
- }finally{
- try {
- in.close();
- } catch (IOException e) {
- e.printStackTrace();
- }
- }
- }
- }
由于BasicConfiguration的实例是static,因此,当类被加载时就会初始化,但这样即使并不需要使用此实例,也会被初始化,导致内存空间的浪费。
方式三:
- package org.jediael.util;
- import java.io.FileInputStream;
- import java.io.FileNotFoundException;
- import java.io.IOException;
- import java.io.InputStream;
- import java.util.Properties;
- public class BasicConfiguration {
- private Properties pros = null;
- private static class ConfigurationHolder{
- private static BasicConfiguration configuration = new BasicConfiguration();
- }
- public static BasicConfiguration getInstance(){
- return ConfigurationHolder.configuration;
- }
- public String getValue(String key){
- return pros.getProperty(key);
- }
- private BasicConfiguration(){
- readConfig();
- }
- private void readConfig() {
- pros = new Properties();
- InputStream in = null;
- try {
- in = new FileInputStream(Thread.currentThread().getContextClassLoader().getResource("")
- .getPath() + "search.properties");
- pros.load(in);
- } catch (FileNotFoundException e) {
- e.printStackTrace();
- }catch (IOException e) {
- e.printStackTrace();
- }finally{
- try {
- in.close();
- } catch (IOException e) {
- e.printStackTrace();
- }
- }
- }
- }
由于初始化放在内部类中,只有当此内部类被使用时,才会进行初始化。从而既节省了空间,也无需同步代码。