public class Main {
	public static void main(String[] args) {
		String s = "123";
		int a = 1;
		changeString(s);
		changeInt(a);
		System.out.println(s); // 123
		System.out.println(a); // 1
	}
	public static void changeString(String tmp) {
	    tmp = "234";
	}
	public static void changeInt(int tmp) {
	    tmp = 3;
	}
}

class Test {
    void print() {
        System.out.println("test");
    }
}
public class Main {

	public static void main(String[] args) {
	    final Test a = new Test();
	    a = new Test();
	}
}
// Main.java:10: error: cannot assign a value to final variable a
// 	    a = new Test();
// 	    ^
// 1 error

package com.example.demo.demos.web;

import org.springframework.web.bind.annotation.*;

@RestController
public class BasicController {

    @RequestMapping("/hello")
    @ResponseBody
    public String hello(@RequestBody String name) {
        return "Hello " + name;
    }
}

package com.example.demo.demos.web;

import lombok.extern.slf4j.Slf4j;
import org.springframework.core.MethodParameter;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.RequestBodyAdvice;

import java.io.IOException;
import java.lang.reflect.Type;
import java.util.Arrays;

@Slf4j
@RestControllerAdvice
public class RequestBodyAdviceImpl implements RequestBodyAdvice {
    @Override
    public boolean supports(MethodParameter methodParameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) {
        return true;
    }

    @Override
    public HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException {
        RequestMapping requestMapping = parameter.getMethodAnnotation(RequestMapping.class);
        log.info("url: " + Arrays.toString(requestMapping.value()));
        log.info("method: " + parameter.getExecutable());
        return inputMessage;
    }

    @Override
    public Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) {
        log.info("param: " + body);
        return body;
    }

    @Override
    public Object handleEmptyBody(Object body, HttpInputMessage inputMessage, MethodParameter parameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) {
        log.info("body: body is Empty");
        return body;
    }
}

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;

public class App {
    public static void main(String[] args) throws Exception {
        String str = "abc";
        InputStream stream = new ByteArrayInputStream(str.getBytes());
        // abc -> acc
        replaceString(stream).stream().forEach( elt -> System.out.println(elt));
	}

    private static List<String> replaceString(InputStream inputStream) throws UnsupportedEncodingException {
        List<String> result = new ArrayList<>();
        FilterInputStream filterInputStream = new FilterInputStream(inputStream) {
            @Override
            public int read(byte[] b, int off, int len) throws IOException {
				int bytesRead = super.read(b, off, len);
				if (bytesRead != -1) {
					for (int i = off; i < off + bytesRead - 1; i++) {
                        // ab -> ac
						if (b[i] == (byte) 0x61 && b[i + 1] == (byte) 0x62) {
							b[i] = (byte) 0x61;
							b[i + 1] = (byte) 0x63;
						}
					}
				}
				return bytesRead;
			}
        };

        BufferedReader br = new BufferedReader(new InputStreamReader(filterInputStream, "UTF8"));
        br.lines().forEach( elt -> {
            result.add(elt);
        });
        return result;
    }
}

public static void printUnicode(String str) {
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        System.out.printf(String.format("\\u%04X ", (int) c));
    }
    System.out.println();
}

Map<String, String> convertMap = new HashMap<>(); 
convertMap.put("\\uFFFD\\u0041", "さい"); 
convertMap.put("\\uFFFD\\u0042", "そね"); 

for (Map.Entry<String, String> entry : convertMap.entrySet()) { 
	String key = entry.getKey(); 
	String value = entry.getValue(); 
    // repaceAll支持直接变换Unicode
	String info = info.replaceAll(key, value); 
}