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在 Java 中如何保存和加载文件中的数据 - 用于文件 I/O 读写操作的简单生产就绪实用程序

已发表: 2020-10-11
在 Java 中如何保存和加载文件中的数据 - 用于文件 I:O 读写操作的简单生产就绪实用程序

如何将对象写入文件并将其读回？

Java 的 API 非常惊人，而在 Java 8 中，我们完全启用了更多的 API，例如 Lambda、方法引用、默认方法、更好的类型接口、重复注释、方法参数反射等等。

前段时间我写了一篇关于如何在 Java 中从文件中读取 JSON 对象的文章。 这是简单的java读取操作。 但在本教程中，我们将使用简单的 Production Ready Java Utility 从文件中save and load数据。

用于文件读取：写入操作的简单生产就绪实用程序

我们不仅保存简单的对象，还将创建 CrunchifyCompany 类型的简单 Java POJO，并使用GSON保存和检索对象。 您需要以下依赖项才能运行以下程序。

将依赖项放在您的 Maven 项目中。 如果您有动态 Web 项目并希望将其转换为 Maven 项目，请按照以下步骤操作。

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< dependency >
< groupId > com . google . code . gson < / groupId >
< artifactId > gson < / artifactId >
< version > 2.3 < / version >
< / dependency >

这是一个流程：

  • 创建类CrunchifyReadWriteUtilityForFile.java
  • 创建具有两个字段的私有内部类CrunchifyCompany
    • 私人内部employees ；
    • 私人字符串companyName ；
  • 在 main 方法中创建对象crunchify
  • 将对象转换为Gson ，以便将其保存到文件中
  • 使用方法crunchifyWriteToFile将数据保存到 Java 中的文件
  • 使用方法crunchifyReadFromFile从 Java 文件中检索数据

这是一个完整的例子：

Java
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package crunchify . com . tutorial ;
 
import com . google . gson . Gson ;
import com . google . gson . stream . JsonReader ;
 
import java . io . * ;
import java . nio . charset . StandardCharsets ;
 
/**
* @author Crunchify.com
* Best and simple Production ready utility to save/load
* (read/write) data from/to file
*/
 
public class CrunchifyReadWriteUtilityForFile {
private static final String crunchifyFileLocation = "/Users/appshah/Documents/crunchify.txt" ;
private static final Gson gson = new Gson ( ) ;
// CrunchifyComapny Class with two fields
// - Employees
// - CompanyName
private static class CrunchifyCompany {
private int employees ;
private String companyName ;
public int getEmployees ( ) {
return employees ;
}
public void setEmployees ( int employees ) {
this . employees = employees ;
}
public String getCompanyName ( ) {
return companyName ;
}
public void setCompanyName ( String companyName ) {
this . companyName = companyName ;
}
}
// Main Method
public static void main ( String [ ] args ) {
CrunchifyCompany crunchify = new CrunchifyCompany ( ) ;
crunchify . setCompanyName ( "Crunchify.com" ) ;
crunchify . setEmployees ( 4 ) ;
// Save data to file
crunchifyWriteToFile ( gson . toJson ( crunchify ) ) ;
// Retrieve data from file
crunchifyReadFromFile ( ) ;
}
// Save to file Utility
private static void crunchifyWriteToFile ( String myData ) {
File crunchifyFile = new File ( crunchifyFileLocation ) ;
// exists(): Tests whether the file or directory denoted by this abstract pathname exists.
if ( ! crunchifyFile . exists ( ) ) {
try {
File directory = new File ( crunchifyFile . getParent ( ) ) ;
if ( ! directory . exists ( ) ) {
// mkdirs(): Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories.
// Note that if this operation fails it may have succeeded in creating some of the necessary parent directories.
directory . mkdirs ( ) ;
}
// createNewFile(): Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist.
// The check for the existence of the file and the creation of the file if it does not exist are a single operation
// that is atomic with respect to all other filesystem activities that might affect the file.
crunchifyFile . createNewFile ( ) ;
} catch ( IOException e ) {
crunchifyLog ( "Exception Occurred: " + e . toString ( ) ) ;
}
}
try {
// Convenience class for writing character files
FileWriter crunchifyWriter ;
crunchifyWriter = new FileWriter ( crunchifyFile . getAbsoluteFile ( ) , true ) ;
// Writes text to a character-output stream
BufferedWriter bufferWriter = new BufferedWriter ( crunchifyWriter ) ;
bufferWriter . write ( myData . toString ( ) ) ;
bufferWriter . close ( ) ;
crunchifyLog ( "Company data saved at file location: " + crunchifyFileLocation + " Data: " + myData + "\n" ) ;
} catch ( IOException e ) {
crunchifyLog ( "Hmm.. Got an error while saving Company data to file " + e . toString ( ) ) ;
}
}
// Read From File Utility
public static void crunchifyReadFromFile ( ) {
// File: An abstract representation of file and directory pathnames.
// User interfaces and operating systems use system-dependent pathname strings to name files and directories.
File crunchifyFile = new File ( crunchifyFileLocation ) ;
if ( ! crunchifyFile . exists ( ) )
crunchifyLog ( "File doesn't exist" ) ;
InputStreamReader isReader ;
try {
isReader = new InputStreamReader ( new FileInputStream ( crunchifyFile ) , StandardCharsets . UTF_8 ) ;
JsonReader myReader = new JsonReader ( isReader ) ;
CrunchifyCompany company = gson . fromJson ( myReader , CrunchifyCompany . class ) ;
crunchifyLog ( "Company Name: " + company . getCompanyName ( ) ) ;
int employee = company . getEmployees ( ) ;
crunchifyLog ( "# of Employees: " + Integer . toString ( employee ) ) ;
} catch ( Exception e ) {
crunchifyLog ( "error load cache from file " + e . toString ( ) ) ;
}
crunchifyLog ( "\nCompany Data loaded successfully from file " + crunchifyFileLocation ) ;
}
private static void crunchifyLog ( String string ) {
System . out . println ( string ) ;
}
}

Eclipse 控制台输出：

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Company data saved at file location : / Users / appshah / Documents / crunchify . txt Data : { "employees" : 4 , "companyName" : "Crunchify.com" }
 
Company Name : Crunchify . com
# of Employees: 4
 
Company Data loaded successfully from file / Users / appshah / Documents / crunchify . txt

这是一个 crunchify.txt 文件内容。

当我运行程序two times时，您会在这里看到两次 JSONObject，因为我们将值附加到crunchify.txt文件。

如何在 Java 中将对象保存到文件 - Crunchify