1.根据方法名，获取类的对应的方法
Method changeSessionIdMethod = ReflectionUtils.findMethod(HttpServletRequest.class, "changeSessionId");
if(changeSessionIdMethod == null) {
throw new IllegalStateException("HttpServletRequest.changeSessionId is undefined. Are you using a Servlet 3.1+ environment?");
}
System.out.println(changeSessionIdMethod);
2.休眠当前线程
TimeUnit.MILLISECONDS.sleep(1000);
3. 替换配置文件中特殊的变量将变量中含有 @{test.test} 将变量 test.test 替换为系统中的其他值。
private static final PropertyPlaceholderHelper helper = new PropertyPlaceholderHelper("@{", "}", ":", false);
private static final PlaceholderResolver placeholderResolver=new PlaceholderResolver(){
@Override
public String resolvePlaceholder(String key) {
return System.getProperty(key);
}
};
4.获取对象的方法名称。dubbo 获取dubbo接口里的方法
String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
5. {0} 字符串格式化。
String template="test1={0},test2={1},test3={2}";
Object[] objects=new Object[]{0,1,"test2"};
String emailContent = MessageFormat.format(template, objects);
System.out.println(emailContent);
6.spring HiddenHttpMethodFilter 将http里post方法转化为参数里的方法
@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
HttpServletRequest requestToUse = request;
if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
String paramValue = request.getParameter(this.methodParam);
if (StringUtils.hasLength(paramValue)) {
requestToUse = new HttpMethodRequestWrapper(request, paramValue);
}
}
filterChain.doFilter(requestToUse, response);
}
7.判断classpath 中是否存在某个类 原理：先判断是否是基础类型， 再 根据 ClassLoader clToUse = classLoader; (clToUse != null ? clToUse.loadClass(name) : Class.forName(name))
org.springframework.util.ClassUtils
if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
&& !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
9.获取classpath下的文件，和 jar包里的文件。
public static void main(String[] args) throws Exception {
Enumeration<URL> urls = ClassLoader.getSystemResources("META-INF/services/ch.qos.logback.classic.spi.Configurator");
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
System.out.println(url.getPath());
}
}
// 从url 读取文件内容
BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), "utf-8"));
10.向目录里写文件，目录和文件不能直接用字符串链接，如目录为：.，文件名为：test.log，直接链接为.log会出错。
public class FileUtil {
public static File getFile(String path,String fileName) throws IOException{
File directory=new File(path);
String filePath=directory.getCanonicalPath();
return new File(filePath+"/"+fileName);
}
}
11.字符串按字节长度截取
public static byte[] subBytes(byte[] src, int begin, int count) {
byte[] bs = new byte[count];
System.arraycopy(src, begin, bs, 0, count);
return bs;
}
if (!StringUtil.isNullOrEmpty(po.getContent())){
byte[] contentB= new byte[0];
try {
contentB = po.getContent().getBytes("utf-8");
if (contentB.length>1024){
po.setContent(new String(StringUtil.subBytes(contentB,0,1024),"utf-8"));
}
} catch (UnsupportedEncodingException e) {
String result="content bytes length > 1024，convert error";
po.setContent(result);
log.error(result,e);
}
}
12.获取类的调用链路
private Class<?> deduceMainApplicationClass() {
try {
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
for (StackTraceElement stackTraceElement : stackTrace) {
if ("main".equals(stackTraceElement.getMethodName())) {
return Class.forName(stackTraceElement.getClassName());
}
}
}
catch (ClassNotFoundException ex) {
// Swallow and continue
}
return null;
}