<apex:page controller="UploadAttachmentController" >
<apex:sectionHeader title="Attach File to {!resIns.Name}" />
<apex:form >
<apex:PageBlock >
<apex:pageMessages />

<apex:pageBlockSection columns="1" id="ttt">
<apex:outputlabel ><b>1.Select the file to upload</b></apex:outputLabel>
<apex:outputlabel >Type the path of the file or click the Browse button to find the file.</apex:outputlabel> 
<apex:inputFile id="file_File" value="{!att.body}" filename="{!att.name}"/>
<apex:outputlabel ><b>2.Click the "Attach File" button.</b></apex:outputLabel>
<apex:outputlabel >Repeat steps 1 and 2 to attach multiple files.</apex:outputlabel>
<apex:outputlabel >( When the upload is complete the file information will appear below. )</apex:outputlabel>
<apex:commandButton id="uploadBtn" value="Attach File" action="{!uploadAttachment}"/>
</apex:pageBlockSection>
<apex:pageBlockSection columns="1">
<apex:outputlabel ><b>3. Click the Done button to return to the previous page.</b></apex:outputLabel>
<apex:outputlabel >( This will cancel an in-progress upload.)</apex:outputlabel> 
<apex:commandButton id="uploadBttn" value="Done" action="{!Done}"/>
</apex:pageBlockSection>

<apex:pageBlockSection title="You have uploaded the file" rendered="{!show}" columns="1">
<apex:pageBlockSectionItem >
File Name :- <apex:outputText value="{!savedAttName}"></apex:outputText>
</apex:pageBlockSectionItem>
<apex:pageBlockSectionItem >
File Size :- <apex:outputText value="{!savedAttSize}"></apex:outputText>
</apex:pageBlockSectionItem>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form> 
</apex:page>

public class UploadAttachmentController {
Public id conId{get;set;}
public Attachment att{Get;set;}
public boolean show{get;set;}
public string size{get;set;} 
public string savedAttName{get;set;}
public double savedAttSize {get;set;}
public RestorationDocument__c resIns {get;set;}

public UploadAttachmentController() { 
string idValue = ''; 
conId = ApexPages.currentPage().getParameters().get('id'); 
resIns = [SELECT id,Name from RestorationDocument__c where Id =: conId];
if(ApexPages.currentPage().getParameters().get('otherIds') != null){
idValue = ApexPages.currentPage().getParameters().get('otherIds');
show = true;
} 
if(idValue != ''){ 
for(Attachment att : [select id, body, name from attachment where id =: idValue])
{
savedAttName = att.name;
savedAttSize = att.body.size();
} 
} 
if(att == null){
att = new Attachment();
}
} 

public pageReference uploadAttachment(){
List<Attachment> attList = new List<Attachment>();
att.IsPrivate = true;
att.parentId = conId;
if(att.body != null)
attList.add(att);
if(attList.size() > 0){
Insert attList ; 
pageReference pgRe = new pageReference('/apex/UploadAttachmentPage?id='+conId+'&otherIds='+att.Id);
pgRe.setredirect(true); 
return pgRe;
}else {
if(!ApexPages.hasMessages())
ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR,'Please Select the File'));
return null;
}

} 
public PageReference Done(){ 
PageReference pageRef = new PageReference('/'+conId);
return pageRef; 
} 
}