Java study notes - document literacy and Json array

Java file read and write

In Java I / O streams there are many ways to read and write files, read the following three major after Baidu

The first way: using the FileReader and FileWriter, reading the contents of the file by character, as follows

String dir = "E:\\soft\\aaa\\a.txt";
File file = new File(dir);
//如果文件不存在，创建文件
if (!file.exists()) 
    file.createNewFile();
//创建FileWriter对象
FileWriter writer = new FileWriter(file);
//向文件中写入内容
writer.write("the first way to write and read");
writer.flush();
writer.close();

//创建FileReader对象，读取文件中的内容
FileReader reader = new FileReader(file);
char[] ch = new char[100];
reader.read(ch);
for(char c:ch) {
    System.out.print(c);
}
System.out.println();
reader.close();

The second way: using packaging BuffredReader BufferedWriter, and, the entire contents of the file to read the line, as follows

String dir = "E:\\soft\\aaa\\b.txt";
File file = new File(dir);
//如果文件不存在，创建文件
if (!file.exists()) 
    file.createNewFile();
//创建BufferedWriter对象并向文件写入内容
BufferedWriter bw = new BufferedWriter(new FileWriter(file));
//向文件中写入内容
bw.write("the second way to write and read");
bw.flush();
bw.close();
//创建BufferedReader读取文件内容
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line=br.readLine())!=null) {
    System.out.println(line);
}
br.close();

The third way: Use a FileOutputStream and FileInputStream, this method writes a file in bytes, the first byte array is read when reading the file, then the byte array into a string, as follows:

String dir = "E:\\soft\\aaa\\c.txt";
File file = new File(dir);
//如果文件不存在，创建文件
if (!file.exists()) 
    file.createNewFile();
//创建FileOutputStream对象，写入内容
FileOutputStream fos = new FileOutputStream(file);
//向文件中写入内容
fos.write("the third way to write and read".getBytes());
fos.close();
//创建FileInputStream对象，读取文件内容
FileInputStream fis = new FileInputStream(file);
byte[] bys = new byte[100];
while (fis.read(bys, 0, bys.length)!=-1) {
    //将字节数组转换为字符串
    System.out.println(new String(bys));
}
fis.close();

The whole class codes:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileRW {

//第一种方式：使用FileWriter和FileReader
public void firstWay() throws IOException {
    String dir = "E:\\soft\\aaa\\a.txt";
    File file = new File(dir);
    //如果文件不存在，创建文件
    if (!file.exists()) 
        file.createNewFile();
    //创建FileWriter对象
    FileWriter writer = new FileWriter(file);
    //向文件中写入内容
    writer.write("the first way to write and read");
    writer.flush();
    writer.close();

     //创建FileReader对象，读取文件中的内容
     FileReader reader = new FileReader(file);
     char[] ch = new char[100];
     reader.read(ch);
     for(char c:ch) {
         System.out.print(c);
     }
     System.out.println();
     reader.close();
}

//第二种方式:使用BuffredReader和BufferedWriter
public void secondWay() throws IOException {
    String dir = "E:\\soft\\aaa\\b.txt";
    File file = new File(dir);
    //如果文件不存在，创建文件
    if (!file.exists()) 
        file.createNewFile();
    //创建BufferedWriter对象并向文件写入内容
    BufferedWriter bw = new BufferedWriter(new FileWriter(file));
    //向文件中写入内容
    bw.write("the second way to write and read");
    bw.flush();
    bw.close();
    //创建BufferedReader读取文件内容
    BufferedReader br = new BufferedReader(new FileReader(file));
    String line;
    while ((line=br.readLine())!=null) {
        System.out.println(line);
    }
    br.close();
}

//第三种方式：使用FileInputStream和FileOutputStream
public void thirdWay() throws IOException {
    String dir = "E:\\soft\\aaa\\c.txt";
    File file = new File(dir);
    //如果文件不存在，创建文件
    if (!file.exists()) 
        file.createNewFile();
    //创建FileOutputStream对象，写入内容
    FileOutputStream fos = new FileOutputStream(file);
    //向文件中写入内容
    fos.write("the third way to write and read".getBytes());
    fos.close();
    //创建FileInputStream对象，读取文件内容
    FileInputStream fis = new FileInputStream(file);
    byte[] bys = new byte[100];
    while (fis.read(bys, 0, bys.length)!=-1) {
        //将字节数组转换为字符串
        System.out.println(new String(bys));
    }
    fis.close();
}

public static void main(String[] args) throws IOException {
    FileRW fileRW = new FileRW();
    fileRW.firstWay();
    fileRW.secondWay();
    fileRW.thirdWay();
}

Results are as follows:

the first way to write and read
the second way to write and read
the third way to write and read

Java generated Json array

Sample Code

import com.google.gson.*;
public class Main{    
public static void main(String[] args) {        
    //创建一个json对象，相当于一个容器，当然这个容器还可以套在另外一个容器里面，这个看业务需要        
    JsonObject jsonContainer =new JsonObject();        
    //为当前的json对象添加键值对        
    jsonContainer.addProperty("category", "nba");        
    jsonContainer.addProperty("team", "lakers");       
    //构建json数组，数组里面也是json        
    JsonArray arrayPlayer = new JsonArray();        
    //构建json数组中的对象        
    JsonObject player1 = new JsonObject();        
    player1.addProperty("name", "kobe");        
    player1.addProperty("height", "198cm");        
    player1.addProperty("weight", "115kg");        
    JsonObject player2 = new JsonObject();        
    player2.addProperty("name", "fisher");        
    player2.addProperty("height", "183cm");        
    player2.addProperty("weight", "85kg");        
    //将json对象添加到数组中        
    arrayPlayer.add(player1);        
    arrayPlayer.add(player2);        
    //最后将json数组装到jsonContainer中        
    jsonContainer.add("player", arrayPlayer);        
    System.out.println(jsonContainer);    
}
}

operation result

{"category":"nba","team":"lakers","player":[{"name":"kobe","height":"198cm","weight":"115kg"},{"name":"fisher","height":"183cm","weight":"85kg"}]}

Formatted as:

{
    "category": "nba",
    "team": "lakers",
    "player": [{
        "name": "kobe",
        "height": "198cm",
        "weight": "115kg"
    }, {
        "name": "fisher",
        "height": "183cm",
        "weight": "85kg"
    }]
}

Wherein JsonObjectgenerating "{}", JsonArrayto generate "[]" may be used addPropertyto add data to "{}", a adddata is added to "[]" in