一些 Java 里常用的代码片段，例如 Bean to String 等。
Bean to String
使用 Apache Commons Lang3
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| import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import org.apache.commons.lang3.builder.ToStringBuilder;
System.out.println(ReflectionToStringBuilder.toString(obj));
System.out.println(ReflectionToStringBuilder.toString(obj, ToStringStyle.MULTI_LINE_STYLE));
System.out.println(ToStringBuilder.reflectionToString(p));
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使用 Fastjson 格式化为 JSON 字符串更漂亮
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| import com.alibaba.fastjson.JSON;
System.out.println(JSON.toJSONString(box));
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或则使用 Lombok 的 @ToString 自动生成字符串也不错
取得当前的方法名
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| Thread.currentThread().getStackTrace()[1].getMethodName()
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Spring 获取 HttpServletRequest
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| HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getRequest();
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SpringSecurity 获取登陆用户名
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| String username = SecurityContextHolder.getContext().getAuthentication().getName();
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Servlet 获取客户端的 IP
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public static String getClientIp(HttpServletRequest request) {
final String UNKNOWN = "unknown";
String ip = request.getHeader("X-Forwarded-For");
if (ip == null || ip.length() == 0 || UNKNOWN.equalsIgnoreCase(ip)) {
ip = request.getHeader("X-Real-IP");
}
if (ip == null || ip.length() == 0 || UNKNOWN.equalsIgnoreCase(ip)) {
ip = request.getHeader("Proxy-Client-IP");
}
if (ip == null || ip.length() == 0 || UNKNOWN.equalsIgnoreCase(ip)) {
ip = request.getHeader("WL-Proxy-Client-IP");
}
if (ip == null || ip.length() == 0 || UNKNOWN.equalsIgnoreCase(ip)) {
ip = request.getHeader("HTTP_CLIENT_IP");
}
if (ip == null || ip.length() == 0 || UNKNOWN.equalsIgnoreCase(ip)) {
ip = request.getHeader("HTTP_X_FORWARDED_FOR");
}
if (ip == null || ip.length() == 0 || UNKNOWN.equalsIgnoreCase(ip)) {
ip = request.getRemoteAddr();
}
return ip;
}
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Nginx 的配置参考:
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| location / {
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://app_server;
add_header Cache-Control 'no-store';
}
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参考 HTTP 请求头中的 X-Forwarded-For
X-Forwarded-For 是用于记录代理信息的，每经过一级代理(匿名代理除外)，代理服务器都会把这次请求的来源 IP 追加在 X-Forwarded-For 中，例如来自 4.4.4.4 的一个请求，header 包含这样一行 X-Forwarded-For: 1.1.1.1, 2.2.2.2, 3.3.3.3 代表请求由 1.1.1.1 发出，经过三层代理，第一层是 2.2.2.2，第二层是 3.3.3.3，而本次请求的来源 IP 4.4.4.4 是第三层代理。
X-Real-IP，一般只记录真实发出请求的客户端 IP，上面的例子，如果配置了 X-Read-IP，将会是 X-Real-IP: 1.1.1.1 1所以 ，如果只有一层代理，这两个头的值就是一样的
字符串 MD5
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| import org.springframework.util.DigestUtils;
public class Test {
public static void main(String[] args) {
System.out.println(DigestUtils.md5DigestAsHex("Biao".getBytes()));
}
}
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文件的 MD5
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| import org.springframework.util.DigestUtils;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class Test {
public static String fileMd5(String path) {
try (InputStream in = new FileInputStream(path)) {
return DigestUtils.md5DigestAsHex(in);
} catch (IOException e) {
e.printStackTrace();
}
return "";
}
public static void main(String[] args) {
System.out.println(fileMd5("/Users/Biao/Desktop/x.png"));
}
}
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生成 UUID
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| import java.util.UUID;
public static String uuid() {
return UUID.randomUUID().toString().replace("-", "").toUpperCase();
}
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读文件自动关闭流
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| import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class Test {
public static void main(String[] args) {
String path = "/Users/Biao/Documents/workspace/Java/mix/src/main/java/Test.java";
try (BufferedReader reader = new BufferedReader(new FileReader(path))) {
String line = null;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
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定期执行任务
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| import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class Test {
public static void main(String[] args) {
ScheduledExecutorService.scheduleAtFixedRate(() -> {
System.out.println(System.currentTimeMillis() / 1000);
}, 0, 1, TimeUnit.SECONDS);
}
}
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过滤后映射
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| import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
Integer[] ns = {1, 2, 3, 4, 5};
Stream.of(ns).filter(n -> n >= 3).mapToInt(n -> n * 2).forEach(System.out::println);
}
}
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- 过滤: 去掉不要的
- 映射: 每一个元素映射为对应的值，一个输入对应一个输出
创建线程
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| public class Test {
public static void main(String[] args) {
new Thread(() -> System.out.println(1)).start();
new Thread(new Runnable() {
@Override
public void run() {
System.out.println(2);
}
}).start();
}
}
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内存映射
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| import java.io.FileInputStream;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class Test {
public static void main(String[] args) throws Exception {
FileInputStream in = new FileInputStream("/Users/Biao/Desktop/1.cpp");
long size = in.available();
FileChannel inChannel = in.getChannel();
MappedByteBuffer inBuffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, size);
RandomAccessFile out = new RandomAccessFile("/Users/Biao/Desktop/2.cpp", "rw");
FileChannel outChannel = out.getChannel();
MappedByteBuffer outBuffer = outChannel.map(FileChannel.MapMode.READ_WRITE, 0, size);
outBuffer.put(inBuffer);
inChannel.close();
outChannel.close();
in.close();
out.close();
}
}
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大小写不敏感的正则表达式
在前面加上 (?i) 即可
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| String name = "names.NSF".replaceAll("(?i)\\.nsf$", "");
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文件路径
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PropUtil.class.getClassLoader().getResourceAsStream("prop.properties");
PropUtil .class.getClassLoader().getResourceAsStream("/prop.properties");
new FileInputStream("prop.properties");
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不存在所谓的 JAVASE 默认根路径的说法，java（无论是 J2SE 还是，J2EE, Web）中只有 classpath，看你的 java 命令怎么配置 classpath。
指定编译和运行时字符集
编译时使用参数 encoding
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| javac -encoding utf-8 Test.java
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运行时使用参数 -Dfile.encoding
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| java -jar -Dfile.encoding=utf-8 Test.jar
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| import java.text.MessageFormat;
public class Test {
public static void main(String[] argv) throws Exception {
Object[] params = { new Integer(123), new Double(1222234.567) };
String msg = MessageFormat.format("{0,number,percent} and {1,number,,###.##}", params);
System.out.println(msg);
}
}
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SpringSecurity iframe
SpringSecurity 默认不让 iframe 嵌入当前站点的网页的，连同域都不允许，可以配置 http 让其允许
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| <http auto-config="true">
<headers>
<frame-options policy="SAMEORIGIN"/>
</headers>
</http>
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查看 SpringMVC Application Context 中的对象
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| WebApplicationContext webApplicationContext = ContextLoader.getCurrentWebApplicationContext();
String[] names = webApplicationContext.getBeanDefinitionNames();
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Easypoi 导入导出 Excel
直接使用 POI 导入导出 Excel 需要写很多代码，使用 Easypoi 只需要很简单的代码就能完成，请访问 http://www.afterturn.cn/doc/easypoi.html
连接字符串 join
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| public static void main(String[] args) throws Exception {
List<String> strs = new LinkedList<>();
strs.add("1");
strs.add("2");
strs.add("3");
System.out.println(String.join(", ", strs));
}
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