我们通常会将Java应用的配置参数保存在属性文件中,Java应用的属性文件可以是一个正常的基于key-value对,以properties为扩展名的文件,也可以是XML文件.
在本案例中,將会向大家介绍如何通过Java程序输出这两种格式的属性文件,并介绍如何从classpath中加载和使用这两种属性文件。
下面是案例程序代码:
PropertyFilesUtil.java
package com.journaldev.util; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.InputStream; import java.util.Properties; import java.util.Set; public class PropertyFilesUtil { public static void main(String[] args) throws IOException { String propertyFileName = "DB.properties"; String xmlFileName = "DB.xml"; writePropertyFile(propertyFileName, xmlFileName); readPropertyFile(propertyFileName, xmlFileName); readAllKeys(propertyFileName, xmlFileName); readPropertyFileFromClasspath(propertyFileName); } /** * read property file from classpath * @param propertyFileName * @throws IOException */ private static void readPropertyFileFromClasspath(String propertyFileName) throws IOException { Properties prop = new Properties(); prop.load(PropertyFilesUtil.class.getClassLoader().getResourceAsStream(propertyFileName)); System.out.println(propertyFileName +" loaded from Classpath::db.host = "+prop.getProperty("db.host")); System.out.println(propertyFileName +" loaded from Classpath::db.user = "+prop.getProperty("db.user")); System.out.println(propertyFileName +" loaded from Classpath::db.pwd = "+prop.getProperty("db.pwd")); System.out.println(propertyFileName +" loaded from Classpath::XYZ = "+prop.getProperty("XYZ")); } /** * read all the keys from the given property files * @param propertyFileName * @param xmlFileName * @throws IOException */ private static void readAllKeys(String propertyFileName, String xmlFileName) throws IOException { System.out.println("Start of readAllKeys"); Properties prop = new Properties(); FileReader reader = new FileReader(propertyFileName); prop.load(reader); Set<Object> keys= prop.keySet(); for(Object obj : keys){ System.out.println(propertyFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString())); } //loading xml file now, first clear existing properties prop.clear(); InputStream is = new FileInputStream(xmlFileName); prop.loadFromXML(is); keys= prop.keySet(); for(Object obj : keys){ System.out.println(xmlFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString())); } //Now free all the resources is.close(); reader.close(); System.out.println("End of readAllKeys"); } /** * This method reads property files from file system * @param propertyFileName * @param xmlFileName * @throws IOException * @throws FileNotFoundException */ private static void readPropertyFile(String propertyFileName, String xmlFileName) throws FileNotFoundException, IOException { System.out.println("Start of readPropertyFile"); Properties prop = new Properties(); FileReader reader = new FileReader(propertyFileName); prop.load(reader); System.out.println(propertyFileName +"::db.host = "+prop.getProperty("db.host")); System.out.println(propertyFileName +"::db.user = "+prop.getProperty("db.user")); System.out.println(propertyFileName +"::db.pwd = "+prop.getProperty("db.pwd")); System.out.println(propertyFileName +"::XYZ = "+prop.getProperty("XYZ")); //loading xml file now, first clear existing properties prop.clear(); InputStream is = new FileInputStream(xmlFileName); prop.loadFromXML(is); System.out.println(xmlFileName +"::db.host = "+prop.getProperty("db.host")); System.out.println(xmlFileName +"::db.user = "+prop.getProperty("db.user")); System.out.println(xmlFileName +"::db.pwd = "+prop.getProperty("db.pwd")); System.out.println(xmlFileName +"::XYZ = "+prop.getProperty("XYZ")); //Now free all the resources is.close(); reader.close(); System.out.println("End of readPropertyFile"); } /** * This method writes Property files into file system in property file * and xml format * @param fileName * @throws IOException */ private static void writePropertyFile(String propertyFileName, String xmlFileName) throws IOException { System.out.println("Start of writePropertyFile"); Properties prop = new Properties(); prop.setProperty("db.host", "localhost"); prop.setProperty("db.user", "user"); prop.setProperty("db.pwd", "password"); prop.store(new FileWriter(propertyFileName), "DB Config file"); System.out.println(propertyFileName + " written successfully"); prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file"); System.out.println(xmlFileName + " written successfully"); System.out.println("End of writePropertyFile"); } }
当运行这段代码时,writePropertyFile 方法会在生成上述两种格式的属性文件,并將文件存储在工程的根目录下。
writePropertyFile 方法生成的两种属性文件内容:
DB.properties
#DB Config file#Fri Nov 16 11:16:37 PST 2012db.user=user db.host=localhost db.pwd=password
DB.xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"><properties><comment>DB Config XML file</comment> <entry key="db.user">user</entry><entry key="db.host">localhost</entry><entry key="db.pwd">password</entry> </properties>
需要注意的是comment元素,我们在使用prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");
这段代码时第二个参数传入的是注释内容,如果传入null,生成的xml属性文件將没有comment元素。
控制台输出内容如下:
Start of writePropertyFile DB.properties written successfully DB.xml written successfully End of writePropertyFile Start of readPropertyFileDB.properties::db.host = localhostDB.properties::db.user = userDB.properties::db.pwd = passwordDB.properties::XYZ = nullDB.xml::db.host = localhostDB.xml::db.user = userDB.xml::db.pwd = passwordDB.xml::XYZ = null End of readPropertyFile Start of readAllKeysDB.properties:: Key=db.user::value=userDB.properties:: Key=db.host::value=localhostDB.properties:: Key=db.pwd::value=passwordDB.xml:: Key=db.user::value=userDB.xml:: Key=db.host::value=localhostDB.xml:: Key=db.pwd::value=password End of readAllKeys Exception in thread "main" java.lang.NullPointerException at java.util.Properties$LineReader.readLine(Properties.java:434) at java.util.Properties.load0(Properties.java:353) at java.util.Properties.load(Properties.java:341) at com.journaldev.util.PropertyFilesUtil.readPropertyFileFromClasspath(PropertyFilesUtil.java:31) at com.journaldev.util.PropertyFilesUtil.main(PropertyFilesUtil.java:21)
这里报了空指针异常,原因是生成的文件保存在工程的根目录下面,而读取时是从classpath下读取,將上面生成的两个属性文件拷贝到src下再次运行程序即可。
我们通常会将Java应用的配置参数保存在属性文件中,Java应用的属性文件可以是一个正常的基于key-value对,以properties为扩展名的文件,也可以是XML文件.
在本案例中,將会向大家介绍如何通过Java程序输出这两种格式的属性文件,并介绍如何从classpath中加载和使用这两种属性文件。
下面是案例程序代码:
PropertyFilesUtil.java
package com.journaldev.util; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.InputStream; import java.util.Properties; import java.util.Set; public class PropertyFilesUtil { public static void main(String[] args) throws IOException { String propertyFileName = "DB.properties"; String xmlFileName = "DB.xml"; writePropertyFile(propertyFileName, xmlFileName); readPropertyFile(propertyFileName, xmlFileName); readAllKeys(propertyFileName, xmlFileName); readPropertyFileFromClasspath(propertyFileName); } /** * read property file from classpath * @param propertyFileName * @throws IOException */ private static void readPropertyFileFromClasspath(String propertyFileName) throws IOException { Properties prop = new Properties(); prop.load(PropertyFilesUtil.class.getClassLoader().getResourceAsStream(propertyFileName)); System.out.println(propertyFileName +" loaded from Classpath::db.host = "+prop.getProperty("db.host")); System.out.println(propertyFileName +" loaded from Classpath::db.user = "+prop.getProperty("db.user")); System.out.println(propertyFileName +" loaded from Classpath::db.pwd = "+prop.getProperty("db.pwd")); System.out.println(propertyFileName +" loaded from Classpath::XYZ = "+prop.getProperty("XYZ")); } /** * read all the keys from the given property files * @param propertyFileName * @param xmlFileName * @throws IOException */ private static void readAllKeys(String propertyFileName, String xmlFileName) throws IOException { System.out.println("Start of readAllKeys"); Properties prop = new Properties(); FileReader reader = new FileReader(propertyFileName); prop.load(reader); Set<Object> keys= prop.keySet(); for(Object obj : keys){ System.out.println(propertyFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString())); } //loading xml file now, first clear existing properties prop.clear(); InputStream is = new FileInputStream(xmlFileName); prop.loadFromXML(is); keys= prop.keySet(); for(Object obj : keys){ System.out.println(xmlFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString())); } //Now free all the resources is.close(); reader.close(); System.out.println("End of readAllKeys"); } /** * This method reads property files from file system * @param propertyFileName * @param xmlFileName * @throws IOException * @throws FileNotFoundException */ private static void readPropertyFile(String propertyFileName, String xmlFileName) throws FileNotFoundException, IOException { System.out.println("Start of readPropertyFile"); Properties prop = new Properties(); FileReader reader = new FileReader(propertyFileName); prop.load(reader); System.out.println(propertyFileName +"::db.host = "+prop.getProperty("db.host")); System.out.println(propertyFileName +"::db.user = "+prop.getProperty("db.user")); System.out.println(propertyFileName +"::db.pwd = "+prop.getProperty("db.pwd")); System.out.println(propertyFileName +"::XYZ = "+prop.getProperty("XYZ")); //loading xml file now, first clear existing properties prop.clear(); InputStream is = new FileInputStream(xmlFileName); prop.loadFromXML(is); System.out.println(xmlFileName +"::db.host = "+prop.getProperty("db.host")); System.out.println(xmlFileName +"::db.user = "+prop.getProperty("db.user")); System.out.println(xmlFileName +"::db.pwd = "+prop.getProperty("db.pwd")); System.out.println(xmlFileName +"::XYZ = "+prop.getProperty("XYZ")); //Now free all the resources is.close(); reader.close(); System.out.println("End of readPropertyFile"); } /** * This method writes Property files into file system in property file * and xml format * @param fileName * @throws IOException */ private static void writePropertyFile(String propertyFileName, String xmlFileName) throws IOException { System.out.println("Start of writePropertyFile"); Properties prop = new Properties(); prop.setProperty("db.host", "localhost"); prop.setProperty("db.user", "user"); prop.setProperty("db.pwd", "password"); prop.store(new FileWriter(propertyFileName), "DB Config file"); System.out.println(propertyFileName + " written successfully"); prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file"); System.out.println(xmlFileName + " written successfully"); System.out.println("End of writePropertyFile"); } }
当运行这段代码时,writePropertyFile 方法会在生成上述两种格式的属性文件,并將文件存储在工程的根目录下。
writePropertyFile 方法生成的两种属性文件内容:
DB.properties
#DB Config file#Fri Nov 16 11:16:37 PST 2012db.user=user db.host=localhost db.pwd=password
DB.xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE properties SYSTEM " <properties><comment>DB Config XML file</comment><entry key="db.user">user</entry><entry key="db.host">localhost</entry> <entry key="db.pwd">password</entry></properties>
需要注意的是comment元素,我们在使用prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");
这段代码时第二个参数传入的是注释内容,如果传入null,生成的xml属性文件將没有comment元素。
控制台输出内容如下:
Start of writePropertyFile DB.properties written successfully DB.xml written successfully End of writePropertyFile Start of readPropertyFileDB.properties::db.host = localhostDB.properties::db.user = userDB.properties::db.pwd = passwordDB.properties::XYZ = nullDB.xml::db.host = localhostDB.xml::db.user = userDB.xml::db.pwd = passwordDB.xml::XYZ = null End of readPropertyFile Start of readAllKeysDB.properties:: Key=db.user::value=userDB.properties:: Key=db.host::value=localhostDB.properties:: Key=db.pwd::value=passwordDB.xml:: Key=db.user::value=userDB.xml:: Key=db.host::value=localhostDB.xml:: Key=db.pwd::value=password End of readAllKeys Exception in thread "main" java.lang.NullPointerException at java.util.Properties$LineReader.readLine(Properties.java:434) at java.util.Properties.load0(Properties.java:353) at java.util.Properties.load(Properties.java:341) at com.journaldev.util.PropertyFilesUtil.readPropertyFileFromClasspath(PropertyFilesUtil.java:31) at com.journaldev.util.PropertyFilesUtil.main(PropertyFilesUtil.java:21)
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