编码知识点整理
编码知识点整理
编码测试
//eclipse文件编码为utf-8
public class EncodeTest {
public static void main(String[] args) throws Exception {
System.out.println("file_encoding:" + System.getProperty("file.encoding"));
System.out.println("sun_jnu_encoding:" + System.getProperty("sun.jnu.encoding"));
String temp = "龙";
System.out.println(new String(temp.getBytes("utf-8")));
System.out.println(temp);
}
}
Jdk版本
E:>javac -version
javac 1.8.0_181
系统默认编码
E:>chcp
活动代码页: 936
以默认编码编译
E:>javac EncodeTest.java
cmd无法编译，根据错误信息可知编译默认采用GBK
E:>javac EncodeTest.java
EncodeTest.java:5: 错误: 编码GBK的不可映射字符
String temp = "榫?";
^
1 个错误E:>
修改代码
//源文件编码UTF-8
public class EncodeTest {
public static void main(String[] args) throws Exception {
System.out.println("file_encoding:" + System.getProperty("file.encoding"));
System.out.println("sun_jnu_encoding:" + System.getProperty("sun.jnu.encoding"));
String temp = "你好";
//源文件编码转换为GBK后，中文乱码如下
//String temp = "浣犲ソ";
System.out.println(new String(temp.getBytes("utf-8")));
System.out.println(temp);
}
}
以系统默认编码GBK编译源文件，运行时编码GBK
E:>javac EncodeTest.java
E:>java EncodeTest
file_encoding:GBK
sun_jnu_encoding:GBK
娴ｇ姴銈?
浣犲ソ运行时编码UTF-8
E:>java -Dfile.encoding=utf-8 EncodeTest
file_encoding:utf-8
sun_jnu_encoding:GBK
浣犲ソ
浣犲ソ
UTF-8编码的你好编译时使用GBK编码，变为乱码浣犲ソ，JVM以二进制字节流的形式加载class，读取字符串并构建String
运行时指定JVM采用GBK文件编码格式，JVM以GBK格式构建浣犲ソ字符串，使用UTF-8编码格式输出，变为娴ｇ姴銈?
运行时指定JVM采用UTF-8文件编码格式，JVM以UTF-8格式构建浣犲ソ字符串，使用UTF-8编码格式输出，还是浣犲ソ
使用javap -verbose EncodeTest反编译，发现常量池里是浣犲ソ，UTF-8编码的你好编译时使用GBK编码，变为浣犲ソ
Classfile /E:/EncodeTest.class
Last modified 2018-9-19; size 957 bytes
MD5 checksum 85d20101a36bb26c2d43f96dad54040b
Compiled from "EncodeTest.java"
public class EncodeTest
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #19.#30 // java/lang/Object."<init>":()V
#2 = Fieldref #31.#32 // java/lang/System.out:Ljava/io/PrintStream;
#3 = Class #33 // java/lang/StringBuilder
#4 = Methodref #3.#30 // java/lang/StringBuilder."<init>":()V
#5 = String #34 // file_encoding:
#6 = Methodref #3.#35 // java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
#7 = String #36 // file.encoding
#8 = Methodref #31.#37 // java/lang/System.getProperty:(Ljava/lang/String;)Ljava/lang/String;
#9 = Methodref #3.#38 // java/lang/StringBuilder.toString:()Ljava/lang/String;
#10 = Methodref #39.#40 // java/io/PrintStream.println:(Ljava/lang/String;)V
#11 = String #41 // sun_jnu_encoding:
#12 = String #42 // sun.jnu.encoding
#13 = String #43 // 浣犲ソ
#14 = Class #44 // java/lang/String
#15 = String #45 // utf-8
#16 = Methodref #14.#46 // java/lang/String.getBytes:(Ljava/lang/String;)[B
#17 = Methodref #14.#47 // java/lang/String."<init>":([B)V
#18 = Class #48 // EncodeTest
#19 = Class #49 // java/lang/Object
#20 = Utf8 <init>
#21 = Utf8 ()V
#22 = Utf8 Code
#23 = Utf8 LineNumberTable
#24 = Utf8 main
#25 = Utf8 ([Ljava/lang/String;)V
#26 = Utf8 Exceptions
#27 = Class #50 // java/lang/Exception
#28 = Utf8 SourceFile
#29 = Utf8 EncodeTest.java
#30 = NameAndType #20:#21 // "<init>":()V
#31 = Class #51 // java/lang/System
#32 = NameAndType #52:#53 // out:Ljava/io/PrintStream;
#33 = Utf8 java/lang/StringBuilder
#34 = Utf8 file_encoding:
#35 = NameAndType #54:#55 // append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
#36 = Utf8 file.encoding
#37 = NameAndType #56:#57 // getProperty:(Ljava/lang/String;)Ljava/lang/String;
#38 = NameAndType #58:#59 // toString:()Ljava/lang/String;
#39 = Class #60 // java/io/PrintStream
#40 = NameAndType #61:#62 // println:(Ljava/lang/String;)V
#41 = Utf8 sun_jnu_encoding:
#42 = Utf8 sun.jnu.encoding
#43 = Utf8 浣犲ソ
#44 = Utf8 java/lang/String
#45 = Utf8 utf-8
#46 = NameAndType #63:#64 // getBytes:(Ljava/lang/String;)[B
#47 = NameAndType #20:#65 // "<init>":([B)V
#48 = Utf8 EncodeTest
#49 = Utf8 java/lang/Object
#50 = Utf8 java/lang/Exception
#51 = Utf8 java/lang/System
#52 = Utf8 out
#53 = Utf8 Ljava/io/PrintStream;
#54 = Utf8 append
#55 = Utf8 (Ljava/lang/String;)Ljava/lang/StringBuilder;
#56 = Utf8 getProperty
#57 = Utf8 (Ljava/lang/String;)Ljava/lang/String;
#58 = Utf8 toString
#59 = Utf8 ()Ljava/lang/String;
#60 = Utf8 java/io/PrintStream
#61 = Utf8 println
#62 = Utf8 (Ljava/lang/String;)V
#63 = Utf8 getBytes
#64 = Utf8 (Ljava/lang/String;)[B
#65 = Utf8 ([B)V
{
public EncodeTest();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 1: 0
public static void main(java.lang.String[]) throws java.lang.Exception;
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=5, locals=2, args_size=1
0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
3: new #3 // class java/lang/StringBuilder
6: dup
7: invokespecial #4 // Method java/lang/StringBuilder."<init>":()V
10: ldc #5 // String file_encoding:
12: invokevirtual #6 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
15: ldc #7 // String file.encoding
17: invokestatic #8 // Method java/lang/System.getProperty:(Ljava/lang/String;)Ljava/lang/String;
20: invokevirtual #6 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
23: invokevirtual #9 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
26: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
29: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
32: new #3 // class java/lang/StringBuilder
35: dup
36: invokespecial #4 // Method java/lang/StringBuilder."<init>":()V
39: ldc #11 // String sun_jnu_encoding:
41: invokevirtual #6 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
44: ldc #12 // String sun.jnu.encoding
46: invokestatic #8 // Method java/lang/System.getProperty:(Ljava/lang/String;)Ljava/lang/String;
49: invokevirtual #6 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
52: invokevirtual #9 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
55: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
58: ldc #13 // String 浣犲ソ
60: astore_1
61: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
64: new #14 // class java/lang/String
67: dup
68: aload_1
69: ldc #15 // String utf-8
71: invokevirtual #16 // Method java/lang/String.getBytes:(Ljava/lang/String;)[B
74: invokespecial #17 // Method java/lang/String."<init>":([B)V
77: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
80: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
83: aload_1
84: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
87: return
LineNumberTable:
line 3: 0
line 4: 29
line 5: 58
line 6: 61
line 7: 80
line 8: 87
Exceptions:
throws java.lang.Exception
}
SourceFile: "EncodeTest.java"
WinHex查看class文件
以UTF-8对源文件编码，运行时编码为GBK
E:>javac -encoding utf-8 EncodeTest.java
E:>java EncodeTest
file_encoding:GBK
sun_jnu_encoding:GBK
浣犲ソ
你好E:>java -Dfile.encoding=utf-8 EncodeTest
file_encoding:utf-8
sun_jnu_encoding:GBK
你好
你好
UTF-8编码的你好编译时使用UTF-8编码，class文件常量池里面是你好
运行时指定JVM采用GBK文件编码格式，JVM以GBK格式构建你好字符串，使用UTF-8编码格式输出，变为浣犲ソ
运行时指定JVM采用UTF-8文件编码格式，JVM以UTF-8格式构建你好字符串，使用UTF-8编码格式输出，还是你好
反编译javap -verbose EncodeTest后，常量池内是你好
WinHex查看class文件
