출처 : http://www.mkyong.com/java/how-to-convert-java-map-to-from-json-jackson/

In this tutorial, we will show you few Jackson examples to convert JSON string to/from a Map.

P.S All examples are tested with Jackson 2.6.3

1. JSON string to Map

package com.mkyong.json;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonMapExample {

	public static void main(String[] args) {

		try {

			ObjectMapper mapper = new ObjectMapper();
			String json = "{\"name\":\"mkyong\", \"age\":29}";

			Map<String, Object> map = new HashMap<String, Object>();

			// convert JSON string to Map
			map = mapper.readValue(json, new TypeReference<Map<String, String>>(){});

			System.out.println(map);

		} catch (JsonGenerationException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

Output

{name=mkyong, age=29}

2. Map to JSON string

Example to convert the Map to JSON string.

package com.mkyong.json;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class MapJsonExample{

	public static void main(String[] args) {

		try {

			ObjectMapper mapper = new ObjectMapper();
			String json = "";

			Map<String, Object> map = new HashMap<String, Object>();
			map.put("name", "mkyong");
			map.put("age", 29);

			// convert map to JSON string
			json = mapper.writeValueAsString(map);

			System.out.println(json);

			json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(map);

			// pretty print
			System.out.println(json);

		} catch (JsonGenerationException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

Output

{"name":"mkyong","age":29}
{
  "name" : "mkyong",
  "age" : 29
}

3. Map to JSON File

package com.mkyong.json;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonMapFileExample {

	public static void main(String[] args) {

		try {

			ObjectMapper mapper = new ObjectMapper();

			Map<String, Object> map = new HashMap<String, Object>();
			map.put("name", "mkyong");
			map.put("age", 29);

			List<Object> list = new ArrayList<>();
			list.add("msg 1");
			list.add("msg 2");
			list.add("msg 3");

			map.put("messages", list);

			// write JSON to a file
			mapper.writeValue(new File("c:\\user.json"), map);

		} catch (JsonGenerationException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

{"name":"mkyong","messages":["msg 1","msg 2","msg 3"],"age":29}

4. JSON file to Map

package com.mkyong.json;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Map;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Jackson2Example {

	public static void main(String[] args) {

		try {

			ObjectMapper mapper = new ObjectMapper();

			// read JSON from a file
			Map<String, Object> map = mapper.readValue(
					new File("c:\\user.json"), 
					new TypeReference<Map<String, Object>>() {
			});

			System.out.println(map.get("name"));
			System.out.println(map.get("age"));

			@SuppressWarnings("unchecked")
			ArrayList<String> list = (ArrayList<String>) map.get("messages");

			for (String msg : list) {
				System.out.println(msg);
			}

		} catch (JsonGenerationException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

Output

mkyong
29
msg 1
msg 2
msg 3

References

1. Wikipedia : JSON
2. Jackson – High-performance JSON processor
3. Jackson 2 – Object to / from JSON

출처 : http://noritersand.tistory.com/240

라이브러리 다운로드

http://wiki.fasterxml.com/JacksonDownload

 jackson-annotations-2.2.3.jar

 jackson-core-2.2.3.jar

 jackson-databind-2.2.3.jar

Map - JSON 변환

writeValueAsString( value )

readValue( arg, type )

● Map

맵 타입이 JSON 형식의 String 타입으로 변환된다. 자바스크립트에 JSON을 넘겨줄 때 유용하다. 

이와 반대로 JSON을 맵 타입으로 변환하려면 다음처럼 작성한다:

● List<Map>

다음은 view에 전달할 model이 List<map<?, ?>> 타입일 때 이를 JSON으로 변환하는 방법이다.

사용방법은 크게 다르지 않고 writeValueAsString, readValue 메서드를 사용하되 타입 명시만 달리한다.

tomcat 에 힙사이즈 설정

catalina.sh 파일에 아래 내용 추가

export CATALINA_OPTS="-Djava.awt.headless=true -server -Xms2048m -Xmx2048m -Xmn1024m

                      -XX:NewSize=512m -XX:MaxNewSize=512m -XX:PermSize=512m -XX:MaxPermSize=512m 

                      -XX:+UseParNewGC -XX:+UseConcMarkSweepGC

                      -XX:SurvivorRatio=4 -XX:+PrintHeapAtGC -XX:+HeapDumpOnOutOfMemoryError"

• CATALINA_OPTS="-server -Xss256k -Xms256m -Xmx512m -XX:NewSize=256m -XX:MaxNewSize=256m -XX:MaxPermSize=128m -XX:SurvivorRatio=5 -XX:ReservedCodeCacheSize=128m -XX:+DisableExplicitGC -XX:+UseConcMarkSweepGC -Djava.net.preferIPv4Stack=true -Djava.awt.headless=true "

-Xmx1024m -Xms1024m -XX:MaxNewSize=384m -XX:MaxPermSize=128m

힙덤프

-XX:-HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=./java_pid<pid>.hprof

GC 옵션

-XX:ParallelGCThreads=2 -XX:-UseConcMarkSweepGC

GC 로그 옵션

-XX:-PrintGC -XX:-PrintGCDetails -XX:-PrintGCTimeStamps -XX:-TraceClassUnloading -XX:-TraceClassLoading

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=$CATALINA_BASE/logs

http://helloworld.naver.com/helloworld/184615

표 3 모니터링 후 옵션변경 예시

두개의 Tomcat을 설치하여 server.xml의 포트 부분을 변경하는 방법도 있지만 

너무 번거러운 관계로 server.xml에서 service 부분만 추가하여 포트를 변경하는 방법이다.

<Service name="Catalina">

    <Connector 

        port="8080"

        redirectPort="8443"

        minSpareThreads="25"

        connectionTimeout="20000"

        maxThreads="500"

        maxSpareThreads="75">

    </Connector>

    <Connector

        port="8009"

        redirectPort="8443"

        protocol="AJP/1.3">

    </Connector>

    <Engine

        defaultHost="localhost"

        name="Catalina">

      <Realm className="org.apache.catalina.realm.UserDatabaseRealm"/>

      <Host

          appBase="webapps"

          name="localhost">

       <!-- 아래의 Context 부분은 Tomcat 버전에 따라 따로 설정할 수 있다. -->

       <!--<Context path="/test" docBase="C:\text" debug="0" reloadable="true"/>-->

      </Host>

    </Engine>

  </Service>

  <Service name="Catalina2">

    <Connector

        port="8081"

        redirectPort="8444"

        minSpareThreads="25"

        connectionTimeout="20000"

        maxThreads="500"

        maxSpareThreads="75">

    </Connector>

    <Connector

        port="8010"

        redirectPort="8444"

        protocol="AJP/1.3">

    </Connector>

    <Engine

        defaultHost="localhost"

        name="Catalina2">

      <Realm className="org.apache.catalina.realm.UserDatabaseRealm"/>

      <Host

          appBase="webapps"

          name="localhost">

       <!-- 아래의 Context 부분은 Tomcat 버전에 따라 따로 설정할 수 있다. -->

       <!--<Context path="/test" docBase="C:\text" debug="0" reloadable="true"/>-->

       </Host>

    </Engine>

  </Service>