Object to JSON Conversion

Below code uses Jackson Json API to convert an Object into a JSON String

We will be converting Person class which has Company instance composed in it.

class Person {
 String name;
 int age;
 Company company;
 
 /**
  * @return the company
  */
 public Company getCompany() {
  return company;
 }
 
 public Person(String name, int age, Company company){
  this.name = name;
  this.age = age;
  this.company = company;
 }
 
 /**
  * @return the age
  */
 public int getAge() {
  return age;
 }
 
 /**
  * @return the name
  */
 public String getName() {
  return name;
 }
}

class Company {
 String companyName;
 float salary;
 
 public Company(String companyName, float salary) {
  this.companyName=companyName;
  this.salary = salary;
 }
 
 /**
  * @return the salary
  */
 public float getSalary() {
  return salary;
 }
 /**
  * @return the companyName
  */
 public String getCompanyName() {
  return companyName;
 }
}

If we don't create the getter methods then the below exception will come:

Exception in thread "main" org.codehaus.jackson.map.JsonMappingException: No serializer found for class com.blogspot.javasampleprogram.Person and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )

package com.blogspot.javasampleprogram;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;

import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.map.ObjectMapper;

/**
 * @author http://java-sample-program.blogspot.in/  
 * Object to Json Conversion
 */
public class JsonStringGenerator {
 

 /**
  * Method to get a JSON string representing the object
  * supplied.
  * @param object for which JSON string is required
  * @return Json String
  * @throws IOException
  */
 public static String createJsonString(Object object) throws IOException {
  Writer writer = new StringWriter();
  JsonFactory factory = new JsonFactory();
  JsonGenerator generator = factory.createJsonGenerator(writer);
  generator.setCodec(new ObjectMapper());
  generator.writeObject(object);
  generator.close();
  System.out.println("Json string " + writer.toString());
  return writer.toString();
 }
 
 public static void main(String[] args)  throws IOException {
  Company company = new Company("ABC", 15001.90f);
  Person p1 = new Person("Jason Stathom", 36, company);
  createJsonString(p1);
 }
 
}

Result: {"company":{"salary":15001.9,"companyName":"ABC"},"age":36,"name":"Jason Stathom"}

We will have to add the following Jackson API dependency:

<dependency>
  <groupId>org.codehaus.jackson</groupId>
  <artifactId>com.springsource.org.codehaus.jackson.mapper</artifactId>
  <version>1.4.3</version>
</dependency>

HashMap to JSON String

Below code uses Jackson Json API to convert a HashMap into a JSON String

package com.blogspot.javasampleprogram;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.HashMap;

import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.map.ObjectMapper;

/**
 * @author http://java-sample-program.blogspot.in/  
 * HashMap to Json String generator
 */
public class JsonStringGenerator {
 

 /**
  * Method to convert map into json format
  * @param map with data to be converted into json
  * @return json string
  */
 public static String createJsonString(HashMap jsonMap) throws IOException {
  System.out.println("Map:"+jsonMap);
  Writer writer = new StringWriter();
  JsonGenerator jsonGenerator = new JsonFactory().
        createJsonGenerator(writer);
  ObjectMapper mapper = new ObjectMapper();
  mapper.writeValue(jsonGenerator, jsonMap);
  jsonGenerator.close();
  System.out.println(writer.toString());
  return writer.toString();
 }
 
 public static void main(String[] args)  throws IOException {
  HashMap<String, String> map = new HashMap<String, String>();
  map.put("1", "Jason Stathom");
  map.put("2", "Brad Pitt");
  map.put("3", "Angelina");
  createJsonString(map);
 }
 
}

Result: {"3":"Angelina","2":"Brad Pitt","1":"Jason Stathom"}

We will have to add following dependency:

<dependency>
  <groupId>org.codehaus.jackson</groupId>
  <artifactId>com.springsource.org.codehaus.jackson.mapper</artifactId>
  <version>1.4.3</version>
</dependency>

How to write CLOB fields

Below code shows the way to write CLOB fields to the database:

import java.io.ByteArrayInputStream;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
 * @author http://java-sample-program.blogspot.in/  
 * Write CLOB to database
 */
public class ClobTest {

 public static void main(String[] args) throws Exception{
 Connection con = null;
 CallableStatement stmt = null;
 
 try {
 
  Class.forName("oracle.jdbc.driver.OracleDriver");
  con = DriverManager.getConnection("jdbc:oracle:thin:@IPAddress:Port:Database",
    "username","password");
  stmt = con.prepareCall("{call CLOBTEST.saveClob(?)}");
  String xmlString = "1234567890";
  
  stmt.setAsciiStream(1,new ByteArrayInputStream(xmlString.getBytes()),
     xmlString.getBytes().length);
  
  stmt.execute();
  System.out.println("executed successfully");
  
 }catch(Exception e){
  e.printStackTrace();
 } finally {
  try{
   if(stmt != null){ 
    stmt.close();
   }
   if(con!= null){
    con.close();     
   }
  }catch (SQLException e) {
   e.printStackTrace();
  }
 }
 
 }

}

CLOB to String Conversion

Below code shows the two ways to convert database CLOB to String code.

1) Convert CLOB to String using BufferedReader:

import java.io.BufferedReader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * @author http://java-sample-program.blogspot.in/  
 * Convert CLOB to String using BufferedReader
 */
public class ClobTest {

 public static void main(String[] args) throws Exception{
 Connection con = null;
 PreparedStatement pstmt = null;
 ResultSet rs = null;
 
 try {
 
  Class.forName("oracle.jdbc.driver.OracleDriver");
  con = DriverManager.getConnection("jdbc:oracle:thin:@IPAddress:Port:Database",
    "username","password");
  pstmt = con.prepareStatement("SELECT clobCol FROM TableName");
  rs = pstmt.executeQuery();
  
  while(rs.next()){   
   
   StringBuffer strOut = new StringBuffer();
   String aux;
   try {
    BufferedReader br = new BufferedReader(rs.getClob("clobCol").
      getCharacterStream());
    while ((aux=br.readLine())!=null) {
     strOut.append(aux);
     strOut.append(System.getProperty("line.separator"));
    }
   }catch (Exception e) {
    e.printStackTrace();
   }
   String clobStr = strOut.toString();
   System.out.println(clobStr);
  } 
  
 }catch(Exception e){
  e.printStackTrace();
 } finally {
  try{
   if(pstmt != null){ 
    pstmt.close();
   }
   if(rs!= null){ 
    rs.close();
   }     
   if(con!= null){
    con.close();     
   }
  }catch (SQLException e) {
   e.printStackTrace();
  }
 }
 
 }
 
}

Use the above method if a very large Clob can be returned by the database.

2) Convert CLOB to String using getSubString() method:

import java.io.BufferedReader;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * @author http://java-sample-program.blogspot.in/  
 * Convert CLOB to String using getSubString() method
 */
public class ClobTest {

 public static void main(String[] args) throws Exception{
 Connection con = null;
 PreparedStatement pstmt = null;
 ResultSet rs = null;
 
 try {
 
  Class.forName("oracle.jdbc.driver.OracleDriver");
  con = DriverManager.getConnection("jdbc:oracle:thin:@IPAddress:Port:Database",
    "username","password");
  pstmt = con.prepareStatement("SELECT clobCol FROM TableName");
  rs = pstmt.executeQuery();
  
  while(rs.next()){   
   Clob clob = rs.getClob("clobCol");
   if (clob != null) {  
    String clobStr = clob.getSubString(1, (int) clob.length());
    System.out.println(clobStr);
   }
  } 
  
 }catch(Exception e){
  e.printStackTrace();
 } finally {
  try{
   if(pstmt != null){ 
    pstmt.close();
   }
   if(rs!= null){ 
    rs.close();
   }     
   if(con!= null){
    con.close();     
   }
  }catch (SQLException e) {
   e.printStackTrace();
  }
 }
 
 }
 
}